English terms: Engineering, Physics & Trades

3-way switchEnglish
A switch with one common terminal and two traveler terminals. Two of them, joined by two traveler wires, control one light from two places.
Shop & Trades, Lesson 5.4 (grade 9–12)

4-bit modeEnglish
Sending each 8-bit character as two 4-bit halves over four data wires (D4–D7), saving pins.
Electronics & Microcontrollers, Lesson 8.4 (grade 9–12)

555 timerEnglish
An integrated circuit (8 pins) that produces accurate time delays or continuous pulses, set by external resistors and a capacitor.
Electronics & Microcontrollers, Lesson 5.3 (grade 9–12)

ABS plasticEnglish
A tough, shiny plastic that holds its shape and color well; LEGO bricks have been made of it since 1963.
Grade 5 Engineering & Physics, Lesson 9.2 (grade 5)

absolute zeroEnglish
The lowest possible temperature, 0 K or −273.15 °C, where a gas’s pressure (at constant volume) would fall to zero.
Physics, Lesson 8.5 (grade 11–12)

abutmentEnglish
The strong support at each end of an arch that keeps the ends from spreading apart.
Grade 2 Engineering & Physics, Lesson 2.3 (grade 2) · Grade 3 Engineering & Physics, Lesson 2.3 (grade 3) · Grade 6 Engineering & Physics, Lesson 2.2 (grade 6)

acceleration due to gravityEnglish
g = 9.80\ \text{m/s}^{2} near the Earth’s surface (it varies slightly with location); on the Moon it is 1.62\ \text{m/s}^{2}.
Physics, Lesson 2.3 (grade 11–12)

accelerometerEnglish
A sensor of acceleration; at rest it measures gravity, so it shows which way is down, but vibration makes it noisy.
Engineering Design, Robotics & Drones, Lesson 9.3 (grade 9–12) · Grade 7 Engineering & Physics, Lesson 9.3 (grade 7) · Grade 8 Engineering & Physics, Lesson 4.4 (grade 8)

accident reconstructionEnglish
The engineering work of finding vehicles’ speeds and directions before a crash from the evidence afterward, using momentum and energy.
Physics, Lesson 6.5 (grade 11–12)

accuracyEnglish
How close a measurement is to the true value.
Physics, Lesson 1.3 (grade 11–12)

Ackermann steeringEnglish
Car-style steering in which the front wheels turn at slightly different angles so they follow circles around a common center.
Engineering Design, Robotics & Drones, Lesson 6.2 (grade 9–12)

action and reactionEnglish
Equal and opposite forces: when one object pushes on a second, the second pushes back on the first just as hard.
Grade 5 Engineering & Physics, Lesson 1.2 (grade 5)

activated sludgeEnglish
A mixture of wastewater and living microbes, kept stirred and supplied with air, in which the microbes eat the dissolved pollution.
Grade 7 Engineering & Physics, Lesson 5.3 (grade 7)

active earth pressureEnglish
The sideways pressure soil exerts when the wall moves slightly away from it; p = K_a\gamma z.
Architecture & Civil Engineering, Lesson 8.4 (grade 9–12)

actuatorEnglish
The part that acts, such as a motor, a valve or a light.
Grade 4 Engineering & Physics, Lesson 8.3 (grade 4) · Grade 5 Engineering & Physics, Lesson 8.1 (grade 5) · Grade 6 Engineering & Physics, Lesson 8.1 (grade 6)

additive manufacturingEnglish
Making a part by adding material layer by layer from a digital file (3D printing).
Engineering Design, Robotics & Drones, Lesson 3.4 (grade 9–12) · Shop & Trades, Lesson 8.1 (grade 9–12)

adhesionEnglish
The attraction that holds an adhesive to the surface of another material (the adherend or substrate).
Shop & Trades, Lesson 2.1 (grade 9–12) · Grade 6 Life Science: Animal Design and Behavior, Lesson 8.3 (grade 6)

aerationEnglish
Bubbling air through water to supply oxygen to the microbes.
Grade 7 Engineering & Physics, Lesson 5.3 (grade 7)

aerodynamicEnglish
Shaped to let air flow past smoothly, with less push or twist from the wind.
Grade 5 Engineering & Physics, Lesson 2.4 (grade 5)

aeroelastic flutterEnglish
A self-feeding oscillation in which wind forces on a structure grow with the structure’s own motion, until it twists apart.
Architecture & Civil Engineering, Lesson 6.4 (grade 9–12)

AFCIEnglish
Arc-fault circuit interrupter. Its electronics recognize the ragged current signature of an arc (a damaged cord, a loose connection) and open the circuit before the arc starts a fire.
Shop & Trades, Lesson 5.3 (grade 9–12)

AFUEEnglish
Annual Fuel Utilization Efficiency: the percentage of the fuel’s heat that reaches the house over a season. Standard gas furnaces are about 80%; condensing furnaces 90–98%.
Shop & Trades, Lesson 6.2 (grade 9–12)

age gradingEnglish
Deciding the age group a toy is designed and labeled for, which determines which safety rules apply.
Engineering Design, Robotics & Drones, Lesson 5.5 (grade 9–12)

aggregateEnglish
The sand (fine) and gravel or crushed stone (coarse) that make up most of concrete’s volume.
Architecture & Civil Engineering, Lesson 5.4 (grade 9–12) · Grade 4 Engineering & Physics, Lesson 3.2 (grade 4) · Grade 7 Gardening & Animals, Lesson 3.2 (grade 7) · +2 more

aileronEnglish
A hinged flap on the back edge of a wing that moves up or down to roll an airplane.
Grade 3 Engineering & Physics, Lesson 7.4 (grade 3) · Grade 6 Engineering & Physics, Lesson 7.2 (grade 6)

aileron, elevator, rudderEnglish
Hinged surfaces on the wings (roll), horizontal tail (pitch) and vertical tail (yaw).
Grade 8 Engineering & Physics, Lesson 9.3 (grade 8)

air barrierEnglish
A continuous layer (drywall, sheathing, tape, sealant, foam) that stops air from flowing through the envelope; insulation alone does not stop air.
Shop & Trades, Lesson 4.4 (grade 9–12)

air gapEnglish
The small gap between the armature and the flywheel magnets, often about 0.010 in (0.25 mm); too wide weakens the spark.
Shop & Trades, Lesson 9.4 (grade 9–12)

air resistance (drag)English
The force of air pushing against a moving object; it grows with speed and with the object’s area.
Physics, Lesson 2.3 (grade 11–12)

airfoilEnglish
The curved shape of a wing, seen from the side.
Grade 3 Engineering & Physics, Lesson 7.2 (grade 3) · Grade 4 Engineering & Physics, Lesson 7.2 (grade 4) · Grade 4 Engineering & Physics, Lesson 9.2 (grade 4) · +3 more

air–fuel ratio (AFR)English
The mass of air per mass of fuel; 14.7:1 is the chemically correct (stoichiometric) ratio for gasoline.
Shop & Trades, Lesson 9.3 (grade 9–12)

airplaneEnglish
A flying machine with wings and an engine.
Kindergarten Engineering & Physics, Lesson 7.4 (grade K) · Kindergarten Geography: God Made the Earth: My First Maps, Lesson 8.4 (grade K)

algorithmEnglish
A precise, step-by-step procedure for solving a problem.
Engineering Design, Robotics & Drones, Lesson 7.2 (grade 9–12) · Grade 2 Engineering & Physics, Lesson 8.2 (grade 2) · Grade 3 Engineering & Physics, Lesson 8.2 (grade 3) · +3 more

allianceEnglish
Teams paired together in a match; cooperation with alliance partners is part of the strategy.
Engineering Design, Robotics & Drones, Lesson 6.5 (grade 9–12) · Explore Great Battles · Expert, Stop 3.6 (Ages 14+) · Explore Great Battles · Ranger, Stop 3.6 (Ages 10–13)

all-moving tail (stabilator)English
A horizontal tail that pivots as a whole, used to keep control near and beyond the speed of sound.
Grade 7 Engineering & Physics, Lesson 7.4 (grade 7)

allowable bearing pressureEnglish
The pressure a soil can safely carry, set by the geotechnical engineer to limit both failure and settlement.
Architecture & Civil Engineering, Lesson 8.2 (grade 9–12)

allowable stressEnglish
Strength divided by the design factor; the highest stress permitted in service.
Engineering Design, Robotics & Drones, Lesson 5.2 (grade 9–12)

alloyEnglish
A metal made by mixing a base metal with other elements to improve its properties, such as steel (iron and carbon) or brass (copper and zinc).
Engineering Design, Robotics & Drones, Lesson 3.2 (grade 9–12)

alternate load pathEnglish
A second way for loads to reach the ground if one member is lost, provided by ties, continuity and redundancy.
Architecture & Civil Engineering, Lesson 4.5 (grade 9–12)

alternating currentEnglish
Electric current that switches direction back and forth many times every second (AC).
Grade 4 Engineering & Physics, Lesson 5.1 (grade 4)

alternating current (AC)English
Electric current that reverses direction many times a second; in North America, 60 times a second.
Grade 5 Engineering & Physics, Lesson 5.3 (grade 5) · Grade 7 Engineering & Physics, Lesson 5.1 (grade 7)

alternatorEnglish
The belt-driven generator that recharges the battery and powers the car while the engine runs, usually at about 13.8–14.7 V.
Shop & Trades, Lesson 10.4 (grade 9–12)

amberEnglish
A golden stone made from old tree sap. When rubbed, it picks up bits of straw.
Grade 2 Engineering & Physics, Lesson 4.1 (grade 2)

ammeterEnglish
A meter that measures current. It is connected in series, so all the current passes through it, and has a very low resistance.
Electronics & Microcontrollers, Lesson 1.5 (grade 9–12)

ampacityEnglish
The current a conductor can carry continuously without exceeding its insulation’s temperature rating. In homes, 14 AWG copper is protected at 15 A, 12 AWG at 20 A and 10 AWG at 30 A.
Shop & Trades, Lesson 5.2 (grade 9–12)

amplifierEnglish
A circuit that makes a signal larger, using energy from a power supply.
Electronics & Microcontrollers, Lesson 4.3 (grade 9–12)

analogEnglish
Continuously variable, able to take any value in a range, like a voltage from 0 to 5 V.
Electronics & Microcontrollers, Lesson 7.4 (grade 9–12)

analog and digital signalsEnglish
An analog signal varies continuously (a voltage from 0 to 5 V); a digital signal has only two states (on and off).
Engineering Design, Robotics & Drones, Lesson 7.1 (grade 9–12)

analog inputEnglish
A pin that measures a voltage between 0 and 5 V and reports it as a number from 0 to 1023.
Grade 7 Engineering & Physics, Lesson 4.3 (grade 7)

analog-to-digital converter (ADC)English
A circuit that measures a voltage and gives it as a number. The Uno’s ADC is 10-bit: 0 to 1023 for 0 to 5 V.
Electronics & Microcontrollers, Lesson 7.4 (grade 9–12) · Engineering Design, Robotics & Drones, Lesson 7.1 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 4.4 (grade 8)

analogWrite()English
Sets a PWM output on a pin marked ~ (3, 5, 6, 9, 10, 11 on the Uno) with a value from 0 (always off) to 255 (always on).
Electronics & Microcontrollers, Lesson 7.5 (grade 9–12)

Analytical EngineEnglish
Babbage’s design (from 1834) for a general-purpose mechanical computer with a “store” (memory), a “mill” (processor) and programs on punched cards.
Electronics & Microcontrollers, Lesson 6.5 (grade 9–12)

anchorEnglish
A huge block of concrete at each end that holds the cables down tight.
Grade 2 Engineering & Physics, Lesson 2.4 (grade 2) · Grade 3 Engineering & Physics, Lesson 2.1 (grade 3) · Explore Travel and Faraway Places · Expert, Stop 2.4 (Ages 14+)

anchorageEnglish
The massive block of masonry or concrete at each end that holds the cables’ pull.
Architecture & Civil Engineering, Lesson 6.3 (grade 9–12) · Grade 3 Engineering & Physics, Lesson 2.4 (grade 3) · Grade 4 Engineering & Physics, Lesson 2.4 (grade 4) · +3 more

ANDEnglish
A \cdot B = 1 only when both A and B are 1. Switches in series.
Electronics & Microcontrollers, Lesson 6.1 (grade 9–12)

angleEnglish
How much something is tilted.
Grade 2 Engineering & Physics, Lesson 7.2 (grade 2) · Playing the Odds, Lesson 6.1 (grade 4–7) · Geometry, Lesson 2.3 (grade 9–10) · +1 more

angle of attackEnglish
How much the front edge of a wing is tilted up into the oncoming air.
Grade 3 Engineering & Physics, Lesson 7.2 (grade 3) · Grade 4 Engineering & Physics, Lesson 7.2 (grade 4) · Grade 5 Engineering & Physics, Lesson 7.2 (grade 5) · +3 more

angle of internal friction (φ)English
A measure of a soil’s shear strength; for loose sand about 30°, dense sand up to about 40°.
Architecture & Civil Engineering, Lesson 8.4 (grade 9–12)

angular accelerationEnglish
The rate of change of angular velocity, \alpha, in rad/s².
Physics, Lesson 7.4 (grade 11–12)

angular momentumEnglish
The “spinning momentum” of a turning object, which makes it resist being tipped over.
Grade 5 Engineering & Physics, Lesson 9.1 (grade 5) · Grade 8 Engineering & Physics, Lesson 9.1 (grade 8) · Physics, Lesson 7.5 (grade 11–12)

angular velocityEnglish
How fast an object turns, \omega, in radians per second (2\pi rad = one turn).
Physics, Lesson 7.4 (grade 11–12) · Body Mechanics of Sport, Lesson 1.4 (grade 8–12)

anisotropicEnglish
Having different properties in different directions, like wood (strong along the grain) or a 3D print (weaker between layers).
Engineering Design, Robotics & Drones, Lesson 3.2 (grade 9–12)

anisotropyEnglish
Having different strength in different directions. FDM parts are strongest along their printed lines and weakest when pulled apart between layers.
Shop & Trades, Lesson 8.4 (grade 9–12)

antennaEnglish
A conductor shaped and sized to send or receive radio waves, usually a fraction (often one-quarter or one-half) of the wavelength long.
Grade 7 Engineering & Physics, Lesson 5.4 (grade 7) · Explore Animals, Stop 5.1 (Ages 7–9)

apparent weightEnglish
The force a scale or floor pushes up on you, which is what you feel as your weight; it equals m(g + a) in an elevator accelerating upward at a.
Physics, Lesson 3.3 (grade 11–12) · Physics, Lesson 8.2 (grade 11–12)

apparent weight (g-force)English
The normal force from the seat divided by the rider’s weight; what a rider feels, in multiples of g.
Physics, Lesson 5.5 (grade 11–12)

aqueductEnglish
A bridge that carries water, here a canal, across a valley.
Architecture & Civil Engineering, Lesson 6.2 (grade 9–12) · Grade 1 Engineering & Physics, Lesson 2.3 (grade 1) · Grade 2 Engineering & Physics, Lesson 2.3 (grade 2) · +3 more

arc eyeEnglish
A painful sunburn of the cornea (photokeratitis) from the arc’s ultraviolet light; it usually appears hours after exposure and feels like sand in the eyes.
Shop & Trades, Lesson 7.5 (grade 9–12)

archEnglish
A curved shape built of pieces that press against each other and hold each other up.
Grade 1 Engineering & Physics, Lesson 2.3 (grade 1) · Grade 2 Engineering & Physics, Lesson 2.3 (grade 2) · Grade 3 Engineering & Physics, Lesson 2.3 (grade 3) · +3 more

arch bridgeEnglish
A bridge held up by a curved arch that pushes down into the ground at each end.
Grade 1 Engineering & Physics, Lesson 2.1 (grade 1) · Grade 2 Engineering & Physics, Lesson 2.1 (grade 2)

arch damEnglish
A dam curved upstream that carries the water’s push sideways into the canyon walls, like an arch lying on its side.
Architecture & Civil Engineering, Lesson 8.5 (grade 9–12) · Grade 7 Geography: Regions of the World, Lesson 4.4 (grade 7)

arch-gravity damEnglish
A dam that combines both actions, such as Hoover Dam.
Architecture & Civil Engineering, Lesson 8.5 (grade 9–12) · Grade 4 Engineering & Physics, Lesson 5.3 (grade 4) · Grade 7 Engineering & Physics, Lesson 5.2 (grade 7)

Archimedes’ principleEnglish
The upward push on an object in water equals the weight of the water it pushes aside.
Grade 4 Engineering & Physics, Lesson 6.1 (grade 4) · Grade 5 Engineering & Physics, Lesson 6.1 (grade 5) · Grade 6 Engineering & Physics, Lesson 6.1 (grade 6) · +1 more

Archimedes screwEnglish
A tube or pipe with a spiral inside (or wrapped around it) that lifts water when it is turned.
Grade 3 Engineering & Physics, Lesson 1.4 (grade 3)

architectEnglish
A licensed professional who designs buildings: their plan, form, spaces, materials and how they meet codes and the client’s needs.
Architecture & Civil Engineering, Lesson 1.4 (grade 9–12)

architect’s scaleEnglish
A triangular ruler with eleven scales (from 3⁄32″ = 1′-0″ to 3″ = 1′-0″, plus a full-size 16ths scale), each read in feet, with the inches subdivided at one end.
Architecture & Civil Engineering, Lesson 2.1 (grade 9–12)

area under the curveEnglish
On a velocity–time graph, the area between the line and the time axis equals the displacement (how far the object moved).
Grade 8 Engineering & Physics, Lesson 1.1 (grade 8)

arithmetic meanEnglish
\tfrac{a + b}{2}, the halfway value. Palladio used it, with the geometric and harmonic means, to set the heights of rooms.
Architecture & Civil Engineering, Lesson 3.3 (grade 9–12)

ARM processorEnglish
A family of efficient processor designs that began at Acorn Computers in Cambridge in 1985; they power most phones, the Raspberry Pi and the Pico.
Electronics & Microcontrollers, Lesson 9.1 (grade 9–12)

armature (ignition coil)English
The coil mounted beside the flywheel, with a primary winding of a few hundred turns and a secondary of many thousands.
Shop & Trades, Lesson 9.4 (grade 9–12)

ASE certificationEnglish
Certification from the National Institute for Automotive Service Excellence, earned by passing tests in specific areas and having hands-on work experience.
Shop & Trades, Lesson 10.5 (grade 9–12)

assemblyEnglish
A CAD file that brings several parts together and defines how they are positioned and how they may move relative to one another.
Engineering Design, Robotics & Drones, Lesson 2.5 (grade 9–12)

astableEnglish
A mode with no stable state: the output switches high and low continuously, making a square wave.
Electronics & Microcontrollers, Lesson 5.3 (grade 9–12)

ASTM F963English
The U.S. standard consumer safety specification for toy safety, mandatory for toys sold in the United States.
Engineering Design, Robotics & Drones, Lesson 5.5 (grade 9–12)

atmospheric pressureEnglish
The push of the air around us, about 101,000 newtons on every square meter (about 10 N on every square centimeter) at sea level.
Grade 7 Engineering & Physics, Lesson 1.2 (grade 7) · Physics, Lesson 8.1 (grade 11–12)

attractEnglish
To pull toward.
Grade 2 Engineering & Physics, Lesson 4.1 (grade 2) · Grade 3 Engineering & Physics, Lesson 4.3 (grade 3) · Kindergarten Engineering & Physics, Lesson 4.1 (grade K)

Atwood machineEnglish
Two masses hung from a string over a light, nearly frictionless pulley; the difference in their weights accelerates both.
Physics, Lesson 3.5 (grade 11–12)

auto-darkening helmetEnglish
A helmet whose liquid-crystal lens darkens automatically in a fraction of a millisecond when the arc strikes.
Shop & Trades, Lesson 7.5 (grade 9–12)

automated guided vehicle (AGV)English
A driverless vehicle that follows a guide (a painted line, a buried wire, magnetic tape or markers in the floor) to move materials.
Engineering Design, Robotics & Drones, Lesson 7.5 (grade 9–12)

automatic sprinklerEnglish
A water nozzle held closed by a heat-sensitive glass bulb or metal link that opens by itself in a fire.
Architecture & Civil Engineering, Lesson 7.5 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 3.3 (grade 8)

automatonEnglish
A self-operating machine that follows a fixed sequence built into its mechanism, such as cams, without sensing or deciding.
Engineering Design, Robotics & Drones, Lesson 6.1 (grade 9–12) · Grade 2 Engineering & Physics, Lesson 8.1 (grade 2)

autonomousEnglish
Able to do a job and make some decisions without a person controlling every move.
Grade 3 Engineering & Physics, Lesson 8.1 (grade 3) · Grade 5 Engineering & Physics, Lesson 8.1 (grade 5) · Grade 6 Engineering & Physics, Lesson 8.4 (grade 6)

autonomous navigation (AutoNav)English
Software that lets a rover look at the terrain, judge hazards and choose its own safe path to a goal.
Engineering Design, Robotics & Drones, Lesson 8.2 (grade 9–12)

autonomous vehicleEnglish
A vehicle that senses its surroundings, plans a path and drives itself without a human at the controls.
Grade 7 Engineering & Physics, Lesson 8.3 (grade 7)

autorotationEnglish
Gliding descent with the engine off, in which upward airflow keeps the rotor spinning so the pilot can land safely.
Grade 8 Engineering & Physics, Lesson 7.2 (grade 8)

average densityEnglish
The total mass of the ship and everything in it divided by its total volume, including the air inside. A ship floats if its average density is less than the water’s.
Grade 7 Engineering & Physics, Lesson 6.2 (grade 7)

average speedEnglish
The total distance divided by the total time, even if the object sped up and slowed down along the way.
Grade 6 Engineering & Physics, Lesson 1.1 (grade 6) · Explore Travel and Faraway Places · Ranger, Stop 2.2 (Ages 10–13)

average velocityEnglish
\bar{v} = \Delta x/\Delta t. Average speed is total distance divided by time.
Physics, Lesson 2.2 (grade 11–12)

AWGEnglish
American Wire Gauge. A smaller number means a thicker wire: 14 AWG is thinner than 12 AWG, which is thinner than 10 AWG.
Shop & Trades, Lesson 5.2 (grade 9–12)

axleEnglish
The rod in the middle that a wheel turns on, or turns with.
Grade 1 Engineering & Physics, Lesson 1.2 (grade 1) · Grade 1 Engineering & Physics, Lesson 9.1 (grade 1) · Grade 2 Engineering & Physics, Lesson 1.3 (grade 2) · +3 more

back EMFEnglish
The voltage a spinning motor generates, which opposes the supply; it is why a motor draws much more current when stalled than when running.
Electronics & Microcontrollers, Lesson 8.3 (grade 9–12) · Engineering Design, Robotics & Drones, Lesson 4.5 (grade 9–12)

balance pointEnglish
The outdoor temperature at which a heat pump’s capacity exactly equals the house’s heat loss; below it, backup heat is needed.
Shop & Trades, Lesson 6.4 (grade 9–12)

ball bearingEnglish
Little balls that let one part roll smoothly against another.
Grade 2 Engineering & Physics, Lesson 1.3 (grade 2)

ballastEnglish
Heavy material placed low in a boat to make it more stable.
Grade 4 Engineering & Physics, Lesson 6.2 (grade 4) · Grade 5 Engineering & Physics, Lesson 6.2 (grade 5) · Grade 6 Engineering & Physics, Lesson 6.2 (grade 6) · +1 more

ballast tankEnglish
A tank in a submarine that is filled with water to dive and blown full of air to rise.
Grade 6 Engineering & Physics, Lesson 6.4 (grade 6)

balloon frameEnglish
A light wood frame of sawn studs running the full height of the building from sill to roof, fastened with machine-made nails (1830s onward).
Architecture & Civil Engineering, Lesson 5.1 (grade 9–12) · Shop & Trades, Lesson 4.2 (grade 9–12)

band gapEnglish
The energy an electron loses crossing the junction; it sets the photon’s energy and so the LED’s color.
Electronics & Microcontrollers, Lesson 3.5 (grade 9–12)

bandwidthEnglish
How much information a link can carry each second.
Grade 6 Engineering & Physics, Lesson 5.4 (grade 6)

bang-bang controlEnglish
Feedback that switches the actuator fully on or fully off, often with hysteresis, as in a home thermostat.
Engineering Design, Robotics & Drones, Lesson 7.3 (grade 9–12)

banked curveEnglish
A curve whose surface tilts inward, so part of the track’s push points toward the center of the turn.
Grade 7 Engineering & Physics, Lesson 9.2 (grade 7) · Grade 8 Engineering & Physics, Lesson 1.3 (grade 8) · Physics, Lesson 4.1 (grade 11–12)

barrel vaultEnglish
A continuous half-cylinder of masonry; it pushes outward along its whole length, so it needs thick, continuous walls.
Architecture & Civil Engineering, Lesson 3.2 (grade 9–12)

base and subbaseEnglish
Layers of compacted crushed stone or gravel that spread wheel loads and drain water.
Architecture & Civil Engineering, Lesson 9.4 (grade 9–12)

base, collector, emitterEnglish
The three legs of a bipolar transistor. A small current into the base lets a larger current flow from the collector to the emitter.
Grade 7 Engineering & Physics, Lesson 4.2 (grade 7) · Grade 8 Engineering & Physics, Lesson 4.2 (grade 8)

base of supportEnglish
The area enclosed by the points where an object touches the ground.
Physics, Lesson 7.2 (grade 11–12) · Body Mechanics of Sport, Lesson 1.2 (grade 4–7) · Body Mechanics of Sport, Lesson 1.3 (grade 8–12)

base resistorEnglish
The resistor that sets the base current from a control signal: R_B = (V_\text{control} - 0.7)/I_B.
Electronics & Microcontrollers, Lesson 4.2 (grade 9–12)

base unitEnglish
One of the seven defined SI units. Length is measured in meters (m), mass in kilograms (kg), time in seconds (s).
Physics, Lesson 1.2 (grade 11–12)

basketEnglish
The part that hangs under a balloon and carries the people.
Grade 1 Engineering & Physics, Lesson 7.4 (grade 1)

bathyscapheEnglish
A deep-diving craft with a crew sphere hung beneath a large float filled with gasoline, which is lighter than water.
Grade 6 Engineering & Physics, Lesson 6.4 (grade 6) · Grade 8 Engineering & Physics, Lesson 6.3 (grade 8) · Grade 3 Geography: Around the World: Continents and Oceans, Lesson 5.4 (grade 3)

batteryEnglish
A small container that stores energy and pushes electricity around a circuit.
Grade 1 Engineering & Physics, Lesson 4.1 (grade 1) · Grade 2 Engineering & Physics, Lesson 4.2 (grade 2) · Grade 4 Engineering & Physics, Lesson 4.1 (grade 4) · +3 more

baud rateEnglish
Symbols per second; for a UART, bits per second, such as 9600 or 115200. Named after Émile Baudot.
Electronics & Microcontrollers, Lesson 10.1 (grade 9–12)

beamEnglish
A long, stiff piece that carries a load across a gap.
Grade 1 Engineering & Physics, Lesson 2.2 (grade 1) · Grade 1 Engineering & Physics, Lesson 6.4 (grade 1) · Grade 3 Engineering & Physics, Lesson 2.2 (grade 3) · +3 more

beam bridgeEnglish
A bridge made of a flat, stiff piece that rests on each side, like a log across a creek.
Grade 1 Engineering & Physics, Lesson 2.1 (grade 1) · Grade 2 Engineering & Physics, Lesson 2.1 (grade 2)

beam (girder) bridgeEnglish
A deck carried by beams that bend between supports; simplest and most common, for spans up to about 300 m with steel box girders, usually far less.
Architecture & Civil Engineering, Lesson 6.1 (grade 9–12)

bearing capacityEnglish
The greatest pressure a soil can carry without failing or sinking too much.
Grade 7 Engineering & Physics, Lesson 3.3 (grade 7) · Shop & Trades, Lesson 4.1 (grade 9–12)

bearing pressureEnglish
The force a column or wall presses onto what is beneath it, divided by the contact area: p = F/A, in pascals (N/m²).
Architecture & Civil Engineering, Lesson 1.1 (grade 9–12) · Grade 7 Engineering & Physics, Lesson 3.3 (grade 7)

bearing stressEnglish
The contact pressure between a bolt or pin and the hole it bears against, \sigma_b = F/(dt).
Engineering Design, Robotics & Drones, Lesson 5.1 (grade 9–12)

bearing wallEnglish
A wall that carries the floors and roof above it down to the foundation.
Architecture & Civil Engineering, Lesson 5.2 (grade 9–12)

behavior-based controlEnglish
Organizing a robot’s program as simple behaviors (follow the line, avoid obstacles) with priorities that decide which one is in charge.
Engineering Design, Robotics & Drones, Lesson 7.5 (grade 9–12)

belt driveEnglish
Power transmission by a flexible belt running on pulleys; quiet and cheap, but it can slip unless toothed.
Engineering Design, Robotics & Drones, Lesson 4.4 (grade 9–12) · Trigonometry, Lesson 3.5 (grade 11–12)

bendingEnglish
Loading that makes a beam curve; one face is stretched (tension) and the other squeezed (compression).
Engineering Design, Robotics & Drones, Lesson 5.1 (grade 9–12)

bending momentEnglish
The internal turning effect at a cut in a beam, which causes bending stress; it is largest where the beam is most likely to fail.
Engineering Design, Robotics & Drones, Lesson 5.3 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 2.1 (grade 8)

bending moment (M)English
The internal turning effect in a beam that bends it; for a simply supported beam with a uniform load, M_{\max} = wL^2/8 at midspan.
Architecture & Civil Engineering, Lesson 5.5 (grade 9–12)

Bernoulli’s equationEnglish
Along a streamline in steady flow, P + \tfrac{1}{2}\rho v^2 + \rho gh is constant: where a fluid speeds up, its pressure drops.
Physics, Lesson 8.3 (grade 11–12)

Bernoulli’s principleEnglish
Along a streamline, where a fluid moves faster its pressure is lower: p + \tfrac{1}{2}\rho v^2 = \text{constant}.
Shop & Trades, Lesson 9.3 (grade 9–12)

best-fit lineEnglish
The straight line that passes as close as possible to all of the data points, with points scattered evenly above and below it.
Physics, Lesson 1.4 (grade 11–12)

bevel and backEnglish
The two faces that meet at a chisel’s or plane iron’s edge. The flat back must be truly flat near the edge; the bevel is ground at about 25° and often honed with a slightly steeper secondary bevel.
Shop & Trades, Lesson 3.2 (grade 9–12)

biasEnglish
The steady DC voltages and currents that set a transistor’s operating point, so that the signal can swing up and down without clipping.
Electronics & Microcontrollers, Lesson 4.3 (grade 9–12) · Explore Crafts and Making · Expert, Stop 1.7 (Ages 14+) · Explore Crafts and Making · Ranger, Stop 1.7 (Ages 10–13) · +3 more

bill of materials (BOM)English
A list of every part with its quantity, value, source and cost.
Electronics & Microcontrollers, Lesson 10.4 (grade 9–12) · Engineering Design, Robotics & Drones, Lesson 1.5 (grade 9–12)

BIMEnglish
Building information modeling: a 3D computer model of a building that also stores information about every part, such as materials, cost and schedule.
Grade 8 Engineering & Physics, Lesson 3.2 (grade 8)

bimetallic stripEnglish
Two metals bonded together that expand by different amounts when heated, so the strip bends as the temperature changes.
Grade 5 Engineering & Physics, Lesson 8.3 (grade 5) · Grade 5 Geography: Explorers, Navigators and Missionaries, Lesson 3.2 (grade 5)

binaryEnglish
A way of writing information with only two choices, such as hole or no hole, 1 or 0.
Grade 4 Engineering & Physics, Lesson 8.1 (grade 4) · Grade 8 Engineering & Physics, Lesson 4.1 (grade 8)

biochemical oxygen demand (BOD)English
A measure of how much organic pollution is in water: the oxygen microbes would use up eating it.
Grade 7 Engineering & Physics, Lesson 5.3 (grade 7)

bipolar junction transistor (BJT)English
A transistor made of three layers (NPN or PNP) with terminals called emitter, base and collector. A small base current controls a large collector current.
Electronics & Microcontrollers, Lesson 4.1 (grade 9–12)

bladeEnglish
One of the long, thin wings on a rotor.
Grade 2 Engineering & Physics, Lesson 7.4 (grade 2) · Kindergarten Engineering & Physics, Lesson 9.3 (grade K) · Explore Hospitality and Home, Stop 2.1 (Ages 7–9) · +1 more

blade balanceEnglish
Equal mass on both sides of the blade’s center hole; an unbalanced blade shakes the engine and mower.
Shop & Trades, Lesson 9.5 (grade 9–12)

blind rivetEnglish
A rivet set from one side of the work by pulling a mandrel, used where the back cannot be reached.
Shop & Trades, Lesson 1.5 (grade 9–12)

blob and centroidEnglish
A connected group of pixels of interest, and its average position, used to find where an object is.
Engineering Design, Robotics & Drones, Lesson 8.3 (grade 9–12)

blockEnglish
The wooden or metal case that holds a pulley wheel. Sailors call a pulley a block.
Grade 3 Engineering & Physics, Lesson 1.2 (grade 3) · Kindergarten Engineering & Physics, Lesson 9.4 (grade K) · Tactics & Strategy, Lesson 1.2 (grade 4–7) · +3 more

block and tackleEnglish
A system of pulleys in two blocks with a rope wound between them; its IMA equals the number of rope segments supporting the moving block.
Engineering Design, Robotics & Drones, Lesson 4.1 (grade 9–12) · Grade 1 Engineering & Physics, Lesson 1.4 (grade 1)

block constructionEnglish
The modern shipbuilding method: the hull is built as large steel blocks, each fitted with pipes, cables and paint, then lifted by giant cranes and welded together.
Grade 8 Engineering & Physics, Lesson 6.4 (grade 8)

BluetoothEnglish
A short-range radio standard at 2.4 GHz for linking devices such as earphones, keyboards and phones, developed at Ericsson in the 1990s.
Electronics & Microcontrollers, Lesson 10.2 (grade 9–12)

board footEnglish
A volume of lumber equal to 144 cubic inches: a board 1 inch thick, 12 inches wide and 1 foot long.
Shop & Trades, Lesson 3.1 (grade 9–12) · Home Décor, Costume & Upholstery, Lesson 2.4 (grade 9–12)

boltEnglish
A headed, externally threaded fastener meant to pass through holes in the parts and be tightened by turning a nut.
Shop & Trades, Lesson 1.2 (grade 9–12)

bolt and nutEnglish
A threaded metal pin and the piece that screws onto it, used to fasten parts together so they can be taken apart again.
Grade 3 Engineering & Physics, Lesson 9.4 (grade 3)

Boolean algebraEnglish
Algebra of true and false (1 and 0) with the operations AND (·), OR (+) and NOT (overbar or ′).
Electronics & Microcontrollers, Lesson 6.1 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 4.1 (grade 8)

boomerangEnglish
A curved, spinning throwing toy whose arms are shaped like wings so it flies in a circle back toward the thrower.
Grade 4 Engineering & Physics, Lesson 9.2 (grade 4)

bore and strokeEnglish
The bore is the cylinder’s diameter; the stroke is how far the piston travels from top dead center (TDC) to bottom dead center (BDC).
Shop & Trades, Lesson 9.1 (grade 9–12)

boring and SPTEnglish
A drilled hole for taking samples; the Standard Penetration Test counts the blows of a 63.5 kg hammer falling 760 mm needed to drive a sampler 300 mm (the N-value).
Architecture & Civil Engineering, Lesson 8.1 (grade 9–12)

bounceEnglish
To hit the ground and spring back up.
Kindergarten Engineering & Physics, Lesson 9.2 (grade K)

bowEnglish
The front of a boat.
Grade 1 Engineering & Physics, Lesson 6.2 (grade 1) · Explore Travel and Faraway Places · Ranger, Stop 2.7 (Ages 10–13)

box fillEnglish
The code limit on how many conductors and devices a box may hold, based on its volume: 2.00 in³ per 14 AWG conductor and 2.25 in³ per 12 AWG conductor.
Shop & Trades, Lesson 5.4 (grade 9–12)

Boyle’s lawEnglish
For a gas at constant temperature, pressure times volume stays the same: P1V1 = P2V2. Double the pressure and the volume halves.
Grade 8 Engineering & Physics, Lesson 6.3 (grade 8)

bracingEnglish
Diagonal members that keep a frame of columns and beams from leaning sideways (racking).
Architecture & Civil Engineering, Lesson 3.4 (grade 9–12) · Grade 3 Engineering & Physics, Lesson 9.4 (grade 3) · Grade 4 Engineering & Physics, Lesson 3.4 (grade 4) · +2 more

brainstormingEnglish
Generating many ideas quickly in a group while deferring judgment, building on others’ ideas and welcoming unusual ones.
Engineering Design, Robotics & Drones, Lesson 1.3 (grade 9–12)

brake fadeEnglish
Loss of braking from overheated pads, rotors or boiling brake fluid.
Shop & Trades, Lesson 10.3 (grade 9–12)

brazing and solderingEnglish
Joining with a filler metal that melts below the base metal, which does not melt. Brazing fillers melt above 450 °C (840 °F); soldering fillers melt below it.
Shop & Trades, Lesson 7.3 (grade 9–12)

break-even quantityEnglish
The number of parts at which two processes cost the same; above it the one with the higher fixed cost but lower cost per part wins.
Shop & Trades, Lesson 8.5 (grade 9–12)

brittle fractureEnglish
Sudden cracking with little bending or warning, in which a crack can run through steel at hundreds of meters per second.
Grade 8 Engineering & Physics, Lesson 6.4 (grade 8) · Shop & Trades, Lesson 7.4 (grade 9–12)

brushed DC motorEnglish
A motor in which a coil (armature) turns between magnets, with brushes and a commutator reversing the current every half turn so the torque keeps the same direction.
Engineering Design, Robotics & Drones, Lesson 4.5 (grade 9–12)

BTUEnglish
British thermal unit: the heat needed to raise 1 pound of water by 1 °F, about 1,055 J. Furnaces and air conditioners are rated in BTU per hour; 1\ \text{W} = 3.412\ \text{BTU/h}.
Shop & Trades, Lesson 6.1 (grade 9–12)

bubble diagramEnglish
A quick drawing of spaces as circles sized roughly to their area and linked by lines showing adjacencies.
Architecture & Civil Engineering, Lesson 10.1 (grade 9–12)

bucket truckEnglish
A truck with a long arm that lifts a worker in a bucket up to the wires.
Kindergarten Engineering & Physics, Lesson 5.4 (grade K)

bucklingEnglish
Sudden sideways bending of a compression member at a load far below its crushing strength.
Architecture & Civil Engineering, Lesson 6.4 (grade 9–12) · Grade 5 Engineering & Physics, Lesson 2.1 (grade 5) · Grade 6 Engineering & Physics, Lesson 2.1 (grade 6) · +1 more

bugEnglish
A mistake in a program.
Grade 1 Engineering & Physics, Lesson 8.2 (grade 1) · Grade 2 Engineering & Physics, Lesson 8.2 (grade 2) · Grade 3 Engineering & Physics, Lesson 8.2 (grade 3) · +3 more

building codeEnglish
A law setting minimum standards for the safety of buildings: structure, fire, exits, accessibility, plumbing and more (in the U.S., usually based on the International Building Code).
Architecture & Civil Engineering, Lesson 7.5 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 3.3 (grade 8) · Grade 6 Geography: Physical Geography: The Earth’s Systems, Lesson 3.4 (grade 6)

building permit and inspectionEnglish
Official permission to do construction work, followed by inspections at set stages (footings, framing, rough plumbing and electrical, insulation, final) to confirm the work meets code.
Shop & Trades, Lesson 4.5 (grade 9–12)

bulbous bowEnglish
A rounded bulb below the waterline at the front of a ship, shaped to make a wave that partly cancels the bow wave at the ship’s cruising speed.
Grade 8 Engineering & Physics, Lesson 6.1 (grade 8)

bulkheadEnglish
A wall that divides the inside of a ship into compartments.
Grade 5 Engineering & Physics, Lesson 6.4 (grade 5) · Grade 7 Engineering & Physics, Lesson 6.2 (grade 7)

bundled tubeEnglish
Several tubes joined side by side, which can stop at different heights, like the Sears (Willis) Tower’s nine tubes.
Architecture & Civil Engineering, Lesson 7.3 (grade 9–12)

buoyant forceEnglish
The upward push of water (or any fluid) on an object in it.
Grade 5 Engineering & Physics, Lesson 6.1 (grade 5) · Grade 6 Engineering & Physics, Lesson 6.1 (grade 6) · Physics, Lesson 8.2 (grade 11–12)

buttressEnglish
A thick support built against a wall to keep it from being pushed over.
Grade 3 Engineering & Physics, Lesson 3.2 (grade 3)

buttressed coreEnglish
The Burj Khalifa’s structure: a hexagonal concrete core braced by three wings, each wall buttressing the others, like a three-legged stool.
Architecture & Civil Engineering, Lesson 7.4 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 3.4 (grade 8)

byteEnglish
Eight bits, which can represent 2^8 = 256 values (0 to 255).
Electronics & Microcontrollers, Lesson 6.2 (grade 9–12)

cableEnglish
A thick, strong rope made of many steel wires twisted or bundled together.
Grade 1 Engineering & Physics, Lesson 2.4 (grade 1) · Grade 2 Engineering & Physics, Lesson 2.4 (grade 2) · Grade 3 Engineering & Physics, Lesson 2.1 (grade 3) · +1 more

cable spinningEnglish
Building a suspension cable in place by carrying wires back and forth across the span on a spinning wheel, then compacting and wrapping them.
Architecture & Civil Engineering, Lesson 6.3 (grade 9–12)

cable-stayed bridgeEnglish
A deck held up by straight cables running directly from towers to the deck; spans up to about 1,100 m.
Architecture & Civil Engineering, Lesson 6.1 (grade 9–12) · Grade 6 Engineering & Physics, Lesson 2.3 (grade 6)

CADEnglish
Computer-aided design: software for drawing and modeling objects precisely, beginning with Ivan Sutherland’s Sketchpad in 1963.
Architecture & Civil Engineering, Lesson 2.5 (grade 9–12) · Engineering Design, Robotics & Drones, Lesson 2.4 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 3.2 (grade 8) · +1 more

cadenceEnglish
A cyclist’s pedaling rate in turns per minute (rpm).
Engineering Design, Robotics & Drones, Lesson 4.4 (grade 9–12) · Grade 9 Physical Education & Health, Lesson 1.2 (grade 9)

caissonEnglish
A huge open-bottomed box sunk into a riverbed, pressurized with air to keep water out while workers dig beneath it to reach firm ground for a foundation.
Architecture & Civil Engineering, Lesson 6.3 (grade 9–12) · Grade 5 Engineering & Physics, Lesson 2.3 (grade 5)

caisson disease (the bends)English
Illness caused when workers leave high-pressure air too quickly and dissolved nitrogen forms bubbles in the body.
Architecture & Civil Engineering, Lesson 6.3 (grade 9–12)

caisson (drilled shaft)English
A large-diameter shaft dug or drilled to firm soil or rock and filled with concrete.
Architecture & Civil Engineering, Lesson 8.2 (grade 9–12)

caliperEnglish
The clamp on a disc brake whose hydraulic piston presses the pads against the spinning rotor.
Shop & Trades, Lesson 10.3 (grade 9–12)

camEnglish
A wheel with an odd shape that pushes something up and down as it turns.
Grade 2 Engineering & Physics, Lesson 8.1 (grade 2) · Grade 5 Engineering & Physics, Lesson 9.4 (grade 5)

cam and followerEnglish
A shaped rotating part (cam) that pushes a follower through a planned pattern of motion each turn.
Engineering Design, Robotics & Drones, Lesson 4.3 (grade 9–12)

cam and linkageEnglish
A cam is a shaped wheel that pushes a follower in a set pattern; a linkage is a set of bars and pivots that turns one motion into another.
Electronics & Microcontrollers, Lesson 8.2 (grade 9–12)

camberEnglish
The gentle upward curve of a wing from front to back.
Grade 4 Engineering & Physics, Lesson 7.2 (grade 4) · Grade 5 Engineering & Physics, Lesson 7.1 (grade 5) · Grade 6 Engineering & Physics, Lesson 7.1 (grade 6)

cam-outEnglish
A driver bit climbing out of a screw’s recess under torque, which strips the recess and can slip into the work or your hand.
Shop & Trades, Lesson 1.2 (grade 9–12)

cantileverEnglish
A beam or slab supported at one end only, reaching out into space.
Architecture & Civil Engineering, Lesson 3.5 (grade 9–12) · Grade 4 Engineering & Physics, Lesson 2.3 (grade 4) · Grade 5 Engineering & Physics, Lesson 2.1 (grade 5) · +3 more

cantilever bridgeEnglish
A bridge built out from each pier in balanced arms, often with a short suspended span between arm tips; good for long spans built without falsework.
Architecture & Civil Engineering, Lesson 6.1 (grade 9–12)

capacitance (C)English
Charge stored per volt: C = Q/V. Unit: the farad (F); practical values are in µF, nF and pF.
Electronics & Microcontrollers, Lesson 3.2 (grade 9–12)

capacitorEnglish
Two conductors separated by an insulator (the dielectric). Charge stored on one plate draws an equal and opposite charge to the other.
Electronics & Microcontrollers, Lesson 3.2 (grade 9–12) · Grade 7 Engineering & Physics, Lesson 4.1 (grade 7)

capacity factorEnglish
How much electricity a plant actually makes in a year compared with what it would make running at full power all the time.
Grade 6 Engineering & Physics, Lesson 5.3 (grade 6)

capsizeEnglish
To tip over in the water.
Grade 5 Engineering & Physics, Lesson 6.2 (grade 5)

carbon film / metal filmEnglish
Common resistor types: a thin film of carbon or metal alloy on a ceramic rod, cut in a spiral to set the value. Metal film is more precise (often 1%).
Electronics & Microcontrollers, Lesson 3.1 (grade 9–12)

carbon monoxide (CO)English
A colorless, odorless gas from incomplete combustion that binds to the blood’s hemoglobin about 200 times more strongly than oxygen.
Shop & Trades, Lesson 6.2 (grade 9–12)

cargoEnglish
The goods a ship carries.
Grade 1 Engineering & Physics, Lesson 6.2 (grade 1) · Grade 3 Geography: Around the World: Continents and Oceans, Lesson 8.3 (grade 3)

Carnot efficiencyEnglish
The greatest possible efficiency of any engine working between T_H and T_C (in kelvins): e_{\max} = 1 - T_C/T_H.
Physics, Lesson 8.5 (grade 11–12)

carrierEnglish
A steady wave of fixed frequency that is changed (modulated) to carry information.
Electronics & Microcontrollers, Lesson 10.2 (grade 9–12) · Grade 4 Gardening & Animals, Lesson 2.3 (grade 4) · Grade 8 Life Science: Heredity, Design and Origins, Lesson 1.4 (grade 8)

Cartesian diverEnglish
A small object with an air bubble inside a sealed bottle; squeezing the bottle squeezes the bubble and makes the diver sink.
Grade 6 Engineering & Physics, Lesson 6.4 (grade 6)

cascading failureEnglish
A chain reaction in which one failure shifts load onto other parts, which then overload and fail in turn.
Grade 8 Engineering & Physics, Lesson 5.1 (grade 8)

casein glueEnglish
Glue made from milk protein and lime; it sets chemically and was the first fairly water-resistant woodworking glue.
Shop & Trades, Lesson 2.2 (grade 9–12)

castleEnglish
A strong stone home with thick walls and towers, built long ago for a lord and his people.
Grade 2 Engineering & Physics, Lesson 3.3 (grade 2) · Explore Travel and Faraway Places, Stop 4.3 (Ages 7–9)

catenaryEnglish
The curve of a uniform chain hanging under its own weight: y = a\cosh(x/a).
Architecture & Civil Engineering, Lesson 4.4 (grade 9–12) · Grade 6 Engineering & Physics, Lesson 3.3 (grade 6) · Grade 7 Engineering & Physics, Lesson 2.3 (grade 7)

cathedralEnglish
A large, important church, the home church of a bishop.
Grade 3 Engineering & Physics, Lesson 3.2 (grade 3)

cavitationEnglish
The forming of vapor bubbles in a liquid where its pressure drops below the vapor pressure, and their violent collapse when pressure rises again.
Grade 8 Engineering & Physics, Lesson 6.2 (grade 8)

cellEnglish
One unit of a battery: two different metals with a liquid or paste between them.
Grade 4 Engineering & Physics, Lesson 4.1 (grade 4) · Grade 7 Engineering & Physics, Lesson 5.4 (grade 7) · Grade 4 Gardening & Animals, Lesson 5.1 (grade 4) · +2 more

center of buoyancyEnglish
The center of the underwater part of the hull, where the buoyant force seems to push up.
Grade 5 Engineering & Physics, Lesson 6.2 (grade 5) · Grade 6 Engineering & Physics, Lesson 6.2 (grade 6)

center of buoyancy (B)English
The center of the underwater volume of the hull, where the upward buoyant force acts.
Grade 7 Engineering & Physics, Lesson 6.1 (grade 7)

center of gravityEnglish
The balance point of an object, where its weight seems to be centered.
Grade 3 Engineering & Physics, Lesson 7.3 (grade 3) · Grade 4 Engineering & Physics, Lesson 7.1 (grade 4) · Grade 5 Engineering & Physics, Lesson 6.2 (grade 5) · +3 more

center of gravity (CG)English
The balance point of the aircraft, where its weight acts.
Grade 7 Engineering & Physics, Lesson 7.2 (grade 7) · Grade 8 Engineering & Physics, Lesson 9.3 (grade 8)

center of gravity (G)English
The point where the whole weight of the ship and its cargo can be thought of as acting, straight down.
Grade 7 Engineering & Physics, Lesson 6.1 (grade 7)

center of lift (center of pressure)English
The point where the total lift of the wing can be thought of as acting.
Grade 7 Engineering & Physics, Lesson 7.2 (grade 7)

center of massEnglish
The average position of an object’s mass. When you drop the Slinky, its center of mass falls with acceleration g from the very start.
Grade 8 Engineering & Physics, Lesson 9.2 (grade 8) · Physics, Lesson 7.2 (grade 11–12) · Body Mechanics of Sport, Lesson 1.3 (grade 8–12) · +1 more

centeringEnglish
A wooden frame that holds up the stones of an arch while it is being built.
Grade 3 Engineering & Physics, Lesson 2.3 (grade 3) · Grade 4 Engineering & Physics, Lesson 3.3 (grade 4)

centripetal accelerationEnglish
The acceleration of any object moving in a circle, pointing toward the center: a = v² ÷ r.
Grade 8 Engineering & Physics, Lesson 1.3 (grade 8) · Physics, Lesson 4.1 (grade 11–12)

centripetal forceEnglish
The inward force needed to keep an object moving in a circle: F = mv² ÷ r.
Grade 7 Engineering & Physics, Lesson 9.2 (grade 7) · Grade 8 Engineering & Physics, Lesson 1.3 (grade 8) · Physics, Lesson 4.1 (grade 11–12) · +2 more

certified welderEnglish
A welder who has passed a practical test to a written procedure and code (for example AWS D1.1 for structural steel); the certification covers the process, position and thickness tested.
Shop & Trades, Lesson 7.5 (grade 9–12)

CFMEnglish
Cubic feet per minute of airflow. Residential systems move roughly 350–450 CFM per ton of cooling.
Shop & Trades, Lesson 6.5 (grade 9–12)

chain driveEnglish
Power transmission by a chain on toothed sprockets; it does not slip, carries high loads and works over long distances.
Engineering Design, Robotics & Drones, Lesson 4.4 (grade 9–12)

chain reactionEnglish
A series of events where each one causes the next.
Grade 4 Engineering & Physics, Lesson 1.4 (grade 4)

character LCD (16 × 2)English
A display of 2 rows of 16 characters, each a 5 × 8 dot matrix, controlled by an HD44780-compatible chip.
Electronics & Microcontrollers, Lesson 8.4 (grade 9–12)

chlorine dose and residualEnglish
The dose is how much chlorine is added; the residual is how much remains after it has reacted, still protecting the water in the pipes.
Grade 8 Engineering & Physics, Lesson 5.4 (grade 8)

chokeEnglish
A plate ahead of the venturi that closes to restrict air, making a rich mixture for a cold start.
Shop & Trades, Lesson 9.3 (grade 9–12)

choking hazardEnglish
A small object that can block a young child’s airway if swallowed or inhaled.
Grade 6 Engineering & Physics, Lesson 9.4 (grade 6)

chordEnglish
The long top or bottom member of a truss.
Grade 5 Engineering & Physics, Lesson 2.2 (grade 5) · Grade 7 Engineering & Physics, Lesson 2.2 (grade 7) · Grade 7 Engineering & Physics, Lesson 7.1 (grade 7) · +1 more

chord and webEnglish
The top and bottom members of a truss are the chords; the verticals and diagonals between them are the web.
Architecture & Civil Engineering, Lesson 4.3 (grade 9–12)

chorobatesEnglish
A Roman leveling table about 20 ft long with plumb lines and a water channel on top, described by Vitruvius.
Architecture & Civil Engineering, Lesson 9.1 (grade 9–12)

chromatic aberrationEnglish
Colored fringes in a lens image, caused by different colors refracting by slightly different amounts.
Physics, Lesson 9.4 (grade 11–12)

chronophotographEnglish
Marey’s term for a photograph that records a moving object several times on the same plate at equal time intervals.
Physics, Lesson 2.4 (grade 11–12)

circuitEnglish
A complete loop that electricity can flow around, from the battery and back again.
Grade 1 Engineering & Physics, Lesson 4.1 (grade 1) · Grade 2 Engineering & Physics, Lesson 4.2 (grade 2) · Grade 3 Engineering & Physics, Lesson 4.1 (grade 3) · +3 more

circuit diagramEnglish
A drawing of a circuit using simple standard symbols instead of pictures.
Grade 4 Engineering & Physics, Lesson 4.4 (grade 4)

circulationEnglish
The paths people use to move through a building: halls, stairs, doorways and the clear space within rooms.
Architecture & Civil Engineering, Lesson 2.2 (grade 9–12) · Human Geography, Lesson 4.4 (grade 9–12) · Grade 5 Life Science: The Human Body, Lesson 3.1 (grade 5) · +1 more

civil engineerEnglish
An engineer who designs public works and structures: buildings’ frames, bridges, roads, dams, water and sewer systems. Specialties include structural, geotechnical, transportation, water resources and environmental engineering.
Architecture & Civil Engineering, Lesson 1.4 (grade 9–12)

civil engineeringEnglish
The branch of engineering that designs, builds and maintains public works: bridges, roads, buildings, dams, water and sewer systems, railways and airports.
Grade 8 Engineering & Physics, Lesson 2.4 (grade 8)

clamp timeEnglish
How long a joint must stay under pressure before it can be handled; full cure takes longer.
Shop & Trades, Lesson 2.2 (grade 9–12)

classical ordersEnglish
The systems of column, capital and entablature with set proportions: Doric (stout, plain capital), Ionic (scroll volutes), Corinthian (acanthus leaves, most slender).
Architecture & Civil Engineering, Lesson 3.1 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 3.1 (grade 8)

clearanceEnglish
The designed gap between two parts that must move or fit together, measured per side or on the diameter.
Shop & Trades, Lesson 8.4 (grade 9–12) · Statistics, Lesson 7.4 (grade 11–12)

clearance volumeEnglish
The space left above the piston at top dead center: the combustion chamber.
Shop & Trades, Lesson 9.1 (grade 9–12)

clientEnglish
The person or group who will own and use the building and who pays for its design and construction.
Architecture & Civil Engineering, Lesson 10.1 (grade 9–12) · Home Décor, Costume & Upholstery, Lesson 10.5 (grade 9–12)

clinker-builtEnglish
Built with planks that overlap each other, like shingles on a roof.
Grade 2 Engineering & Physics, Lesson 6.3 (grade 2)

clipperEnglish
A fast sailing ship of the 1800s with a sharp, narrow hull and many sails.
Grade 3 Engineering & Physics, Lesson 6.2 (grade 3) · Technology Overcoming Geography, Lesson 1.5 (grade 9–12)

clipper shipEnglish
A fast sailing ship with a long, narrow, pointed hull and many sails.
Grade 1 Engineering & Physics, Lesson 6.2 (grade 1)

clockEnglish
A steady square wave that tells the parts of a digital system when to change, so they change together.
Electronics & Microcontrollers, Lesson 6.4 (grade 9–12)

closed circuitEnglish
A loop with no gaps. Electricity flows and the bulb lights.
Grade 2 Engineering & Physics, Lesson 4.2 (grade 2)

closed-loop controlEnglish
Control with feedback: the machine measures the result and corrects itself, like a thermostat.
Grade 5 Engineering & Physics, Lesson 8.3 (grade 5)

closed-loop (feedback) controlEnglish
Control that measures the result and uses the error to correct the command (a thermostat).
Engineering Design, Robotics & Drones, Lesson 7.3 (grade 9–12)

clothoid loopEnglish
A loop shaped like a teardrop, tighter at the top than at the bottom, used on modern roller coasters.
Grade 4 Engineering & Physics, Lesson 9.4 (grade 4) · Grade 7 Engineering & Physics, Lesson 1.4 (grade 7) · Grade 8 Engineering & Physics, Lesson 1.4 (grade 8) · +1 more

clutch powerEnglish
LEGO’s name for how firmly bricks hold together: tight enough to stay, loose enough to pull apart.
Grade 5 Engineering & Physics, Lesson 9.2 (grade 5)

coagulation and flocculationEnglish
Adding a chemical (such as alum) that makes tiny particles clump together, then gently stirring so the clumps (floc) grow large enough to settle.
Architecture & Civil Engineering, Lesson 9.2 (grade 9–12)

codeEnglish
Instructions written so that a computer can follow them.
Grade 3 Engineering & Physics, Lesson 8.2 (grade 3) · Grade 4 Engineering & Physics, Lesson 8.2 (grade 4) · Explore Great Battles, Stop 5.5 (Ages 7–9)

code of ethicsEnglish
A profession’s written rules of conduct. Engineering codes begin by requiring engineers to hold paramount the safety, health and welfare of the public.
Architecture & Civil Engineering, Lesson 1.4 (grade 9–12) · Engineering Design, Robotics & Drones, Lesson 8.5 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 8.1 (grade 8)

coefficient of frictionEnglish
The ratio \mu of the friction force to the normal force for a pair of surfaces; usually \mu_k < \mu_s.
Physics, Lesson 3.4 (grade 11–12) · Body Mechanics of Sport, Lesson 3.4 (grade 8–12)

coefficient of friction (μ)English
A number that tells how “grippy” two surfaces are: friction force ÷ normal force. It has no units.
Grade 6 Engineering & Physics, Lesson 1.3 (grade 6) · Grade 7 Engineering & Physics, Lesson 9.2 (grade 7)

coefficient of restitutionEnglish
e = \dfrac{\text{speed of separation}}{\text{speed of approach}}. For a ball bouncing on a hard floor, e = \sqrt{h_{\text{bounce}}/h_{\text{drop}}}. e = 1 is perfectly elastic, e = 0 perfectly inelastic.
Physics, Lesson 6.3 (grade 11–12)

cofferEnglish
A sunken panel in a ceiling or dome, which removes weight while leaving ribs of material.
Architecture & Civil Engineering, Lesson 3.1 (grade 9–12) · Grade 4 Engineering & Physics, Lesson 3.2 (grade 4)

cohesionEnglish
The internal strength that holds the adhesive itself, or any one material, together.
Shop & Trades, Lesson 2.1 (grade 9–12) · Grade 7 Gardening & Animals, Lesson 5.1 (grade 7)

cold jointEnglish
A dull, lumpy joint where the solder did not properly wet the pad or lead, usually because one was not hot enough. It may conduct poorly or crack.
Electronics & Microcontrollers, Lesson 5.2 (grade 9–12) · Grade 7 Engineering & Physics, Lesson 4.4 (grade 7)

cold-cranking amps (CCA)English
The current a battery can deliver for 30 seconds at 0 °F (−18 °C) while staying above 7.2 V; a measure of starting power.
Shop & Trades, Lesson 10.4 (grade 9–12)

collectiveEnglish
The control that changes the pitch (angle) of all main-rotor blades together, raising or lowering total lift.
Grade 8 Engineering & Physics, Lesson 7.2 (grade 8)

collective and cyclic pitchEnglish
On a helicopter, collective changes the pitch of all blades together (more or less lift); cyclic changes it around each turn to tilt the lift.
Engineering Design, Robotics & Drones, Lesson 9.1 (grade 9–12)

collideEnglish
To bump into something while moving.
Grade 1 Engineering & Physics, Lesson 9.2 (grade 1)

color codeEnglish
Bands of color that give a resistor’s value: digits, then a multiplier (a power of ten), then tolerance. Black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, gray 8, white 9.
Electronics & Microcontrollers, Lesson 3.1 (grade 9–12)

combined sewerEnglish
An older system carrying both sewage and stormwater in the same pipes, as in Bazalgette’s London.
Architecture & Civil Engineering, Lesson 9.3 (grade 9–12)

command line (shell)English
A text interface where you type commands and the computer replies. The program that reads your commands is the shell (such as bash or zsh).
Electronics & Microcontrollers, Lesson 9.2 (grade 9–12)

common-emitter amplifierEnglish
The basic BJT amplifier: signal into the base, output from the collector, emitter (through a resistor) to ground. It inverts the signal.
Electronics & Microcontrollers, Lesson 4.3 (grade 9–12)

commutatorEnglish
The part of a motor that reverses the current at just the right moment each turn so the motor keeps spinning.
Grade 5 Engineering & Physics, Lesson 4.2 (grade 5)

comparatorEnglish
A circuit that compares two voltages and gives a high or low output depending on which is larger.
Electronics & Microcontrollers, Lesson 5.3 (grade 9–12)

compartmentationEnglish
Dividing a building into fire-rated compartments so a fire is contained where it starts.
Architecture & Civil Engineering, Lesson 7.5 (grade 9–12)

compile / uploadEnglish
Compiling turns your C++ into machine instructions; uploading sends them over USB into the microcontroller’s flash memory.
Electronics & Microcontrollers, Lesson 7.1 (grade 9–12)

component conservationEnglish
In two dimensions, the total x-momentum and the total y-momentum are each conserved separately.
Physics, Lesson 6.5 (grade 11–12)

component (or group)English
In a 3D model, a set of geometry treated as one object that can be copied; editing one copy of a component changes them all.
Architecture & Civil Engineering, Lesson 2.5 (grade 9–12)

componentsEnglish
The horizontal and vertical parts of a force at an angle: F_x = F\cos\theta, F_y = F\sin\theta.
Architecture & Civil Engineering, Lesson 4.2 (grade 9–12) · Physics, Lesson 1.5 (grade 11–12) · Trigonometry, Lesson 9.4 (grade 11–12)

compositeEnglish
A material made of two or more materials combined so that each improves the other, such as fibers in a resin (fiberglass, carbon fiber) or plywood.
Engineering Design, Robotics & Drones, Lesson 3.2 (grade 9–12)

compound gear trainEnglish
A train in which two gears of different sizes are fixed on one shaft, so ratios multiply.
Engineering Design, Robotics & Drones, Lesson 4.2 (grade 9–12)

compressEnglish
To squeeze into a smaller space.
Grade 3 Engineering & Physics, Lesson 7.1 (grade 3)

compressed airEnglish
Air squeezed into a smaller space, which pushes back harder.
Grade 4 Engineering & Physics, Lesson 9.1 (grade 4)

compressibleEnglish
Able to be squeezed into a smaller volume. Air is very compressible; water hardly at all.
Grade 6 Engineering & Physics, Lesson 6.4 (grade 6)

compression ratioEnglish
The volume in the cylinder when the piston is at the bottom divided by the volume when it is at the top.
Grade 7 Engineering & Physics, Lesson 1.3 (grade 7) · Shop & Trades, Lesson 9.1 (grade 9–12)

compression testEnglish
Measuring the cylinder’s cranking pressure with a gauge in the plug hole to check rings, valves and head gasket.
Shop & Trades, Lesson 9.4 (grade 9–12)

compressive stressEnglish
Force per unit area pressing on a material, \sigma = F/A, in pascals; masonry is strong in compression.
Architecture & Civil Engineering, Lesson 1.3 (grade 9–12)

conceptEnglish
A complete but rough idea for a design, enough to sketch and compare.
Engineering Design, Robotics & Drones, Lesson 1.3 (grade 9–12)

condenserEnglish
A cold chamber where steam turns back into water, leaving a partial vacuum behind it.
Grade 7 Engineering & Physics, Lesson 1.2 (grade 7) · Shop & Trades, Lesson 6.3 (grade 9–12)

condensing furnaceEnglish
A furnace with a second heat exchanger that cools the exhaust enough to condense its water vapor, recovering latent heat; it vents through plastic pipe and drains condensate.
Shop & Trades, Lesson 6.2 (grade 9–12)

condition ratingEnglish
An inspector’s score for a part of a bridge, from 9 (excellent) down to 0 (failed).
Grade 6 Engineering & Physics, Lesson 2.4 (grade 6) · Grade 8 Engineering & Physics, Lesson 2.4 (grade 8)

conditionalEnglish
Code that chooses what to do based on a test (if, else).
Engineering Design, Robotics & Drones, Lesson 7.2 (grade 9–12) · Grade 4 Engineering & Physics, Lesson 8.2 (grade 4) · Grade 5 Engineering & Physics, Lesson 8.2 (grade 5) · +1 more

conduction, convection, radiationEnglish
The three ways heat moves: through a solid by contact, by moving hot air or liquid, and by invisible infrared light.
Grade 8 Engineering & Physics, Lesson 3.3 (grade 8) · Shop & Trades, Lesson 6.1 (grade 9–12)

conductor and insulatorEnglish
In a conductor (metals, salt water) charges move freely; in an insulator (rubber, plastic, glass, dry air) they stay put.
Physics, Lesson 10.1 (grade 11–12)

configuration controlEnglish
Keeping track of every change to a design and making sure everyone affected knows about it.
Engineering Design, Robotics & Drones, Lesson 10.4 (grade 9–12)

connectionEnglish
The part of a structure where members are joined, such as a bolt, weld or nut on a rod. Many failures begin at connections.
Grade 8 Engineering & Physics, Lesson 8.1 (grade 8)

conservation of angular momentumEnglish
When no net external torque acts, a system’s angular momentum stays constant.
Physics, Lesson 7.5 (grade 11–12)

conservation of chargeEnglish
Charge is never created or destroyed; rubbing only moves electrons from one object to another.
Physics, Lesson 10.1 (grade 11–12)

conservation of energyEnglish
Energy is never created or destroyed by a machine; it only changes form or moves from one place to another.
Grade 7 Engineering & Physics, Lesson 1.1 (grade 7) · Grade 8 Engineering & Physics, Lesson 1.4 (grade 8) · Physics, Lesson 5.1 (grade 11–12)

conservation of mechanical energyEnglish
When only gravity and spring forces do work (no friction or air drag), KE + PE stays constant.
Physics, Lesson 5.3 (grade 11–12)

conservation of momentumEnglish
In a collision with no outside force, the total momentum before equals the total momentum after.
Grade 8 Engineering & Physics, Lesson 1.2 (grade 8) · Physics, Lesson 6.2 (grade 11–12)

consolidationEnglish
The slow settlement of a saturated clay as water is squeezed out of its pores under load.
Architecture & Civil Engineering, Lesson 8.1 (grade 9–12) · Grade 7 Engineering & Physics, Lesson 3.3 (grade 7)

constraintsEnglish
The limits on a design, such as the materials, money, time or size allowed.
Grade 5 Engineering & Physics, Lesson 1.1 (grade 5)

construction adhesiveEnglish
A thick, gap-filling adhesive in caulking tubes (synthetic rubber or polyurethane) for subfloors, paneling and framing.
Shop & Trades, Lesson 2.4 (grade 9–12)

construction documentsEnglish
The detailed drawings and specifications (after presentation and approval) from which contractors build.
Architecture & Civil Engineering, Lesson 10.5 (grade 9–12)

construction linesEnglish
Light lines (boxes, centerlines, guides) drawn first to set proportions, then darkened where the object’s edges really are.
Engineering Design, Robotics & Drones, Lesson 2.1 (grade 9–12)

contact angle (θ)English
The angle a liquid drop makes with a solid at its edge: small angles mean good wetting, angles over 90° mean poor wetting.
Shop & Trades, Lesson 2.1 (grade 9–12)

contact cementEnglish
A rubber (often neoprene) adhesive in solvent or water, spread on both surfaces, allowed to dry, then pressed together for an instant bond.
Shop & Trades, Lesson 2.4 (grade 9–12)

continuityEnglish
A test that beeps when two points are connected by a very low resistance, used to check wires and find breaks.
Electronics & Microcontrollers, Lesson 1.5 (grade 9–12) · Grade 7 Engineering & Physics, Lesson 4.4 (grade 7)

continuity equationEnglish
For an incompressible fluid in a pipe, the volume flow rate is the same everywhere: A_1v_1 = A_2v_2.
Physics, Lesson 8.3 (grade 11–12)

controlled airspaceEnglish
Airspace around airports (Class B, C, D and surface Class E) where flights need FAA authorization, obtained for drones through LAANC or DroneZone.
Engineering Design, Robotics & Drones, Lesson 9.4 (grade 9–12)

controllerEnglish
The part that decides what to do based on what the sensor measures; in a robot, usually a computer.
Grade 4 Engineering & Physics, Lesson 8.3 (grade 4) · Grade 5 Engineering & Physics, Lesson 8.1 (grade 5)

conventional currentEnglish
Current drawn as flowing from the positive terminal through the circuit to the negative terminal, the direction Benjamin Franklin chose. Electrons in a wire actually move the other way.
Electronics & Microcontrollers, Lesson 1.1 (grade 9–12)

coolant (antifreeze)English
A mixture of glycol and water, usually 50/50, that carries heat from the engine to the radiator, resists freezing and boiling, and contains corrosion inhibitors.
Shop & Trades, Lesson 10.2 (grade 9–12)

coordinatesEnglish
Two numbers that tell exactly where a point is: how far across and how far up.
Grade 3 Engineering & Physics, Lesson 9.1 (grade 3) · Explore Travel and Faraway Places · Ranger, Stop 1.7 (Ages 10–13) · Grade 3 Geography: Around the World: Continents and Oceans, Lesson 1.4 (grade 3) · +2 more

COPEnglish
Coefficient of performance: heat delivered divided by electrical energy used. Electric resistance heat has COP 1; heat pumps typically 2–4.
Shop & Trades, Lesson 6.4 (grade 9–12)

copyright, trademark and trade secretEnglish
Copyright protects original creative works (text, drawings, code); a trademark protects names and logos that identify a maker; a trade secret is valuable information kept confidential.
Engineering Design, Robotics & Drones, Lesson 10.2 (grade 9–12)

cordEnglish
The covered wire that carries electricity from the outlet to a lamp or machine.
Kindergarten Engineering & Physics, Lesson 4.4 (grade K) · Explore Crafts and Making, Stop 2.2 (Ages 7–9) · Threads & Weaving, Lesson 6.3 (grade 9–12)

coreEnglish
A stiff central tube, often of concrete, around the elevators and stairs that helps a tall building resist sideways loads.
Grade 5 Engineering & Physics, Lesson 3.4 (grade 5) · Grade 5 Engineering & Physics, Lesson 9.3 (grade 5) · Grade 1 Gardening & Animals, Lesson 1.3 (grade 1) · +3 more

corner pieceEnglish
One of the 8 cube pieces with three colored faces.
Grade 5 Engineering & Physics, Lesson 9.3 (grade 5)

corrosionEnglish
Damage to metal by chemical reaction, such as rust on iron and steel.
Grade 6 Engineering & Physics, Lesson 2.4 (grade 6) · Grade 8 Engineering & Physics, Lesson 2.4 (grade 8)

coulomb (C)English
The SI unit of charge: the charge of about 6.24 \times 10^{18} electrons. One electron carries e = 1.602 \times 10^{-19}\ \text{C}.
Electronics & Microcontrollers, Lesson 1.1 (grade 9–12)

Coulomb’s lawEnglish
F = k\dfrac{q_1q_2}{r^2} with k = 8.99 \times 10^9\ \text{N}\cdot\text{m}^{2}\text{/C}^{2}.
Physics, Lesson 10.1 (grade 11–12)

counter-rotationEnglish
Two rotors spinning one way and two the other, so their twisting effects on the frame (torques) cancel.
Grade 7 Engineering & Physics, Lesson 8.4 (grade 7)

counterweightEnglish
A weight on the other end of the ropes, usually equal to the car plus about 40–50% of its rated load, so the motor lifts only the difference.
Architecture & Civil Engineering, Lesson 7.2 (grade 9–12) · Grade 4 Engineering & Physics, Lesson 2.3 (grade 4) · Grade 5 Engineering & Physics, Lesson 3.3 (grade 5) · +3 more

coupling capacitorEnglish
A capacitor that passes the changing signal into or out of a stage while blocking the DC bias.
Electronics & Microcontrollers, Lesson 4.3 (grade 9–12)

covered bridgeEnglish
A wooden bridge with a roof and walls to keep the rain off its wooden frame.
Grade 2 Engineering & Physics, Lesson 2.2 (grade 2)

CPUEnglish
Central processing unit: the control unit, registers and arithmetic logic unit (ALU) that fetch and carry out instructions.
Electronics & Microcontrollers, Lesson 6.5 (grade 9–12)

craneEnglish
A machine for lifting heavy things high.
Grade 1 Engineering & Physics, Lesson 1.4 (grade 1) · Grade 3 Engineering & Physics, Lesson 9.4 (grade 3)

crank and rockerEnglish
A crank turns all the way around; a rocker swings back and forth through an angle.
Engineering Design, Robotics & Drones, Lesson 4.3 (grade 9–12)

crankcase compressionEnglish
Using the sealed crankcase under the piston as a pump: the rising piston draws mixture into it, and the falling piston pushes it up through the transfer ports.
Shop & Trades, Lesson 9.2 (grade 9–12)

crankshaftEnglish
A shaft with offset arms that turns the up-and-down motion of the pistons into rotation.
Grade 7 Engineering & Physics, Lesson 1.3 (grade 7)

C-rateEnglish
Charge or discharge current relative to capacity: 1C for a 2,000 mAh cell is 2.0 A; 0.5C is 1.0 A.
Electronics & Microcontrollers, Lesson 5.4 (grade 9–12) · Engineering Design, Robotics & Drones, Lesson 6.4 (grade 9–12)

criteria and constraintsEnglish
What a design must do, and the limits it must work within (materials, time, cost, size).
Grade 5 Engineering & Physics, Lesson 8.4 (grade 5)

cross slope (crown)English
The sideways slope of a road surface, about 2%, that sheds water to the edges.
Architecture & Civil Engineering, Lesson 9.4 (grade 9–12)

cross-bracingEnglish
Diagonal members, often in an X, that turn the rectangles of a frame into stiff triangles.
Grade 5 Engineering & Physics, Lesson 3.4 (grade 5)

cross-linkingEnglish
Chemical bonds tying polymer chains into one three-dimensional network, so the material can no longer melt.
Shop & Trades, Lesson 2.3 (grade 9–12)

crownEnglish
The high middle of a road, so rain runs off to the sides.
Grade 2 Engineering & Physics, Lesson 5.4 (grade 2) · Fabrics & Sewing II, Lesson 5.4 (grade 6–8) · Home Décor, Costume & Upholstery, Lesson 2.4 (grade 9–12) · +1 more

crumple zoneEnglish
The front and rear parts of a car designed to crush in a controlled way during a crash, stretching out the stopping time.
Grade 8 Engineering & Physics, Lesson 1.2 (grade 8) · Physics, Lesson 6.1 (grade 11–12)

CSVEnglish
Comma-separated values: a plain-text format with one record per line, such as 120,24.8,512, that any spreadsheet can open.
Electronics & Microcontrollers, Lesson 8.5 (grade 9–12)

culvertEnglish
A large tunnel in the lock walls that carries water into or out of the chamber.
Grade 7 Engineering & Physics, Lesson 6.3 (grade 7) · Grade 7 Geography: Regions of the World, Lesson 8.3 (grade 7) · Grade 8 Geography: Rivers, Ports and Straits, Lesson 6.3 (grade 8) · +1 more

current dividerEnglish
Parallel branches split the total current; the smaller resistance takes the larger share.
Electronics & Microcontrollers, Lesson 2.1 (grade 9–12)

current gain (β)English
Collector current ÷ base current. For common small transistors it is often 100 or more.
Grade 7 Engineering & Physics, Lesson 4.2 (grade 7) · Grade 8 Engineering & Physics, Lesson 4.2 (grade 8)

current (I)English
The rate at which electric charge flows past a point, measured in amperes (amps, A). 1 milliamp (mA) = 0.001 A.
Grade 6 Engineering & Physics, Lesson 4.1 (grade 6)

current-limiting resistorEnglish
A resistor in series with an LED that sets its current: R = (V_s - V_F)/I.
Electronics & Microcontrollers, Lesson 3.5 (grade 9–12)

curtain wallEnglish
A non-load-bearing outer wall attached to the frame, carrying only its own weight and wind.
Architecture & Civil Engineering, Lesson 7.1 (grade 9–12) · Grade 3 Engineering & Physics, Lesson 3.4 (grade 3) · Grade 5 Engineering & Physics, Lesson 3.3 (grade 5) · +1 more

cut nailEnglish
A nail sheared from iron or steel plate by machine, with a rectangular, tapered shank and blunt tip; common from about the 1790s to the 1890s.
Shop & Trades, Lesson 1.5 (grade 9–12)

cut planeEnglish
The imaginary horizontal slice of a plan. Walls cut by it are drawn with heavy lines (or filled, called poché); things below it are drawn lighter.
Architecture & Civil Engineering, Lesson 2.2 (grade 9–12)

cutoffEnglish
The transistor is fully off: no base current, almost no collector current; it acts like an open switch.
Electronics & Microcontrollers, Lesson 4.2 (grade 9–12)

cyanoacrylate (CA)English
“Super glue”: a liquid monomer that polymerizes in seconds when it meets traces of moisture on a surface.
Shop & Trades, Lesson 2.4 (grade 9–12)

cyclicEnglish
The control that changes each blade’s pitch as it goes around, tilting the rotor disk so the helicopter moves forward, back or sideways.
Grade 8 Engineering & Physics, Lesson 7.2 (grade 8)

cylinder and pistonEnglish
A tube and a close-fitting plug that slides in it. Gas pressure on the piston turns heat into motion.
Grade 7 Engineering & Physics, Lesson 1.2 (grade 7)

dado and rabbetEnglish
A dado is a square-bottomed groove across the grain that a shelf fits into; a rabbet is a step cut along the edge or end of a board.
Shop & Trades, Lesson 3.4 (grade 9–12)

damage toleranceEnglish
Designing so that cracks are found by inspection and the structure stays safe until they are repaired.
Engineering Design, Robotics & Drones, Lesson 5.4 (grade 9–12)

dampingEnglish
Anything that removes energy from a vibration so it dies away.
Grade 7 Engineering & Physics, Lesson 3.4 (grade 7)

data centerEnglish
A building full of computer servers, network equipment, backup power and cooling, where websites and online services run.
Grade 8 Engineering & Physics, Lesson 5.3 (grade 8)

data loggerEnglish
A device that records measurements automatically at set times, with a time stamp for each.
Electronics & Microcontrollers, Lesson 8.5 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 4.4 (grade 8)

datasheetEnglish
The maker’s document giving a part’s ratings and typical values, such as an LED’s maximum current (often 20–30 mA) and forward voltage.
Electronics & Microcontrollers, Lesson 3.5 (grade 9–12)

dBA and exchange rateEnglish
Sound level in decibels weighted for human hearing. Under the NIOSH guideline, 85 dBA is safe for 8 hours, and every 3 dB louder halves the safe time.
Shop & Trades, Lesson 3.3 (grade 9–12)

DC motorEnglish
A motor in which current in a coil, in the field of a magnet, makes a turning force. A commutator reverses the coil current each half turn so the rotation continues.
Electronics & Microcontrollers, Lesson 8.3 (grade 9–12)

De Morgan’s lawsEnglish
\overline{A \cdot B} = \overline{A} + \overline{B} and \overline{A + B} = \overline{A} \cdot \overline{B}.
Electronics & Microcontrollers, Lesson 6.1 (grade 9–12)

dead loadEnglish
The weight of the building itself: its walls, floors, beams, roof and everything built in.
Grade 5 Engineering & Physics, Lesson 3.1 (grade 5) · Grade 7 Engineering & Physics, Lesson 2.4 (grade 7)

dead load and live loadEnglish
Dead load is the permanent weight of the structure itself; live load is the moving or changing weight on it, such as trains, trucks and people.
Grade 8 Engineering & Physics, Lesson 2.1 (grade 8)

dead load (D)English
The permanent weight of the structure and everything fixed to it: framing, floors, roofing, walls, finishes, fixed equipment.
Architecture & Civil Engineering, Lesson 4.1 (grade 9–12)

dead reckoningEnglish
Working out position from a known start by adding up measured speed (or distance) and heading over time, without outside references.
Engineering Design, Robotics & Drones, Lesson 8.1 (grade 9–12) · Grade 6 Engineering & Physics, Lesson 7.3 (grade 6) · Explore Travel and Faraway Places · Expert, Stop 3.4 (Ages 14+) · +3 more

debugEnglish
To find and fix a mistake in a program.
Grade 1 Engineering & Physics, Lesson 8.2 (grade 1) · Grade 2 Engineering & Physics, Lesson 8.2 (grade 2) · Grade 3 Engineering & Physics, Lesson 8.2 (grade 3) · +1 more

debugging logEnglish
A dated record of each symptom, test, result and change, so that a fault is found once and remembered.
Electronics & Microcontrollers, Lesson 2.5 (grade 9–12)

deckEnglish
The flat part of a bridge that people and cars travel on.
Grade 3 Engineering & Physics, Lesson 2.4 (grade 3) · Grade 4 Engineering & Physics, Lesson 2.4 (grade 4) · Explore Dinosaurs, Stop 4.4 (Ages 7–9) · +1 more

default passwordEnglish
A password set at the factory and shared by many devices of the same model; it must be changed before a device is used.
Electronics & Microcontrollers, Lesson 10.3 (grade 9–12)

defectEnglish
A flaw that makes a weld unacceptable: cracks, porosity, lack of fusion, incomplete penetration, undercut, trapped slag, overlap.
Shop & Trades, Lesson 7.4 (grade 9–12) · Explore Crafts and Making · Ranger, Stop 4.5 (Ages 10–13)

deflectionEnglish
How far a structural member bends under load.
Architecture & Civil Engineering, Lesson 3.5 (grade 9–12) · Grade 6 Engineering & Physics, Lesson 2.1 (grade 6)

deflection limitEnglish
A code limit on how much a beam may sag, such as span/360 under live load for floors.
Architecture & Civil Engineering, Lesson 5.5 (grade 9–12)

deflection theoryEnglish
An analysis method (Moisseiff and others) showing that a suspension bridge’s cables help stiffen its deck, allowing lighter decks; pushed too far, it led to Tacoma Narrows.
Architecture & Civil Engineering, Lesson 6.3 (grade 9–12)

degree of freedom (DOF)English
One independent way a joint can move, such as one rotation or one slide. A rigid object in space has six: three slides and three rotations.
Grade 7 Engineering & Physics, Lesson 8.1 (grade 7)

degree of freedom (robot)English
An independent joint motion; a typical industrial arm has six, enough to place a tool at any position and angle in its reach.
Engineering Design, Robotics & Drones, Lesson 6.1 (grade 9–12)

degrees of freedom (DOF)English
The independent ways a body can move. A free rigid body in space has six: three translations and three rotations.
Engineering Design, Robotics & Drones, Lesson 2.5 (grade 9–12)

delayEnglish
An instruction that makes the program wait, usually measured in milliseconds (ms). 1,000 ms = 1 second.
Grade 6 Engineering & Physics, Lesson 4.4 (grade 6)

delightEnglish
Vitruvius’s third quality: a building must be beautiful and well proportioned.
Grade 6 Engineering & Physics, Lesson 3.2 (grade 6)

dependencyEnglish
A task that cannot start until another is finished.
Engineering Design, Robotics & Drones, Lesson 10.1 (grade 9–12) · Grade 7 Geography: Regions of the World, Lesson 9.2 (grade 7)

derivative gain (Kd)English
How strongly it responds to how fast the error is changing; it damps oscillation, acting like a brake.
Engineering Design, Robotics & Drones, Lesson 7.4 (grade 9–12)

derived unitEnglish
A unit built from base units, such as the newton, 1\ \text{N} = 1\ \text{kg}\cdot\text{m/s}^{2}, or the joule, 1\ \text{J} = 1\ \text{N}\cdot\text{m}.
Physics, Lesson 1.2 (grade 11–12)

descriptive geometryEnglish
Gaspard Monge’s method (1790s) of representing three-dimensional objects exactly with two or more orthographic views.
Architecture & Civil Engineering, Lesson 2.5 (grade 9–12)

design conceptEnglish
The central idea that organizes a design and answers the program and site.
Architecture & Civil Engineering, Lesson 10.1 (grade 9–12)

design factorEnglish
The minimum factor of safety the designer requires, chosen before design according to codes and the consequences of failure.
Engineering Design, Robotics & Drones, Lesson 5.2 (grade 9–12)

design for manufactureEnglish
Designing a product so it can be made and assembled quickly, cheaply and correctly.
Grade 5 Engineering & Physics, Lesson 9.4 (grade 5)

design historyEnglish
The record of what was decided, when and why, so that others can understand, check and improve a design.
Engineering Design, Robotics & Drones, Lesson 1.5 (grade 9–12)

design intentEnglish
What the designer means a part to do and how it should change, expressed by the choice of dimensions and constraints.
Engineering Design, Robotics & Drones, Lesson 2.4 (grade 9–12)

design marginEnglish
Designing something to be stronger or safer than the minimum needed.
Grade 6 Engineering & Physics, Lesson 9.4 (grade 6)

design narrativeEnglish
The short story of a design: the client’s needs, the site, the main idea and how the building answers them.
Architecture & Civil Engineering, Lesson 10.5 (grade 9–12)

design reviewEnglish
A meeting in which the designer presents a design and others question it, to find problems early.
Electronics & Microcontrollers, Lesson 10.5 (grade 9–12) · Engineering Design, Robotics & Drones, Lesson 10.5 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 8.3 (grade 8)

design-bid-buildEnglish
A delivery method in which the owner hires an architect to complete the design, then contractors bid to build it, and the lowest qualified bidder builds.
Architecture & Civil Engineering, Lesson 1.5 (grade 9–12)

design-buildEnglish
A delivery method in which one team, under one contract, both designs and builds the project.
Architecture & Civil Engineering, Lesson 1.5 (grade 9–12)

detention timeEnglish
How long water stays in a basin: volume ÷ flow.
Architecture & Civil Engineering, Lesson 9.2 (grade 9–12)

diagnostic treeEnglish
An ordered set of checks that rules out causes one at a time, beginning with the simplest and most likely.
Shop & Trades, Lesson 9.5 (grade 9–12)

diaphragmEnglish
A thin, flexible sheet that vibrates with sound, inside a telephone or a microphone.
Grade 3 Engineering & Physics, Lesson 5.4 (grade 3) · Grade 5 Life Science: The Human Body, Lesson 4.1 (grade 5)

dielectricEnglish
The insulating layer between a capacitor’s plates: air, glass, ceramic, plastic film, or a thin oxide in an electrolytic.
Electronics & Microcontrollers, Lesson 3.2 (grade 9–12)

differentialEnglish
A gear set that lets the left and right drive wheels turn at different speeds in a turn.
Shop & Trades, Lesson 10.1 (grade 9–12)

differential levelingEnglish
Finding differences in elevation by reading a graduated rod through a level: elevation = known elevation + backsight − foresight.
Architecture & Civil Engineering, Lesson 9.1 (grade 9–12)

differential settlementEnglish
Settlement that is greater on one side of a structure than the other, causing it to tilt.
Architecture & Civil Engineering, Lesson 8.3 (grade 9–12)

differential (tank) driveEnglish
Two independently driven sides; the robot turns by driving one side faster than the other, and can spin in place.
Engineering Design, Robotics & Drones, Lesson 6.2 (grade 9–12)

diffractionEnglish
The spreading of waves around obstacles and through openings.
Physics, Lesson 9.5 (grade 11–12)

diffraction gratingEnglish
A surface with many evenly spaced lines or grooves; light of wavelength \lambda is sent strongly at angles where d\sin\theta = m\lambda.
Physics, Lesson 9.5 (grade 11–12)

digital input/outputEnglish
A pin that is either HIGH (about 5 V, “on”) or LOW (0 V, “off”).
Grade 7 Engineering & Physics, Lesson 4.3 (grade 7)

digital mockupEnglish
A complete computer model of a product used to check fit, clearance and assembly before anything is built.
Engineering Design, Robotics & Drones, Lesson 2.5 (grade 9–12)

digitalRead()English
Reads a pin set as an input and returns HIGH (about 5 V) or LOW (about 0 V).
Electronics & Microcontrollers, Lesson 7.3 (grade 9–12)

dihedralEnglish
The upward angle of the wings from root to tip, seen from the front, which gives roll stability.
Grade 7 Engineering & Physics, Lesson 7.2 (grade 7)

dimensionEnglish
A number written on a drawing that gives the true size; a builder reads the dimension, never measures the drawing, when one is given.
Architecture & Civil Engineering, Lesson 2.1 (grade 9–12)

dimension stringEnglish
A line of chained dimensions along a wall, with an overall dimension outside it; the parts must add to the whole.
Architecture & Civil Engineering, Lesson 2.2 (grade 9–12)

dimensional analysisEnglish
Checking that both sides of an equation have the same units (dimensions).
Physics, Lesson 1.2 (grade 11–12)

diodeEnglish
A two-terminal part that conducts current easily in one direction (anode to cathode) and blocks it in the other. The band marks the cathode.
Electronics & Microcontrollers, Lesson 3.4 (grade 9–12) · Grade 5 Engineering & Physics, Lesson 4.4 (grade 5) · Grade 7 Engineering & Physics, Lesson 4.1 (grade 7)

dipstickEnglish
A metal or plastic blade used to measure the level and condition of engine oil or transmission fluid.
Shop & Trades, Lesson 10.2 (grade 9–12)

direct current (DC)English
Electric current that flows in only one direction, like the current from a battery.
Grade 5 Engineering & Physics, Lesson 5.3 (grade 5) · Grade 7 Engineering & Physics, Lesson 5.1 (grade 7)

directoryEnglish
Another word for folder. ~ means your home directory, . the current one and .. the one above.
Electronics & Microcontrollers, Lesson 9.2 (grade 9–12)

disinfectEnglish
To destroy germs, often with a small amount of chlorine.
Grade 3 Engineering & Physics, Lesson 5.1 (grade 3)

disinfectionEnglish
Destroying remaining harmful microbes, usually with chlorine, ultraviolet light or ozone.
Architecture & Civil Engineering, Lesson 9.2 (grade 9–12) · Grade 5 Engineering & Physics, Lesson 5.1 (grade 5) · Grade 6 Engineering & Physics, Lesson 5.1 (grade 6) · +2 more

disk loadingEnglish
Thrust divided by rotor disk area, T/A; low disk loading means efficient hovering.
Engineering Design, Robotics & Drones, Lesson 9.2 (grade 9–12)

dispatchableEnglish
A power source that operators can turn up or down when needed.
Grade 6 Engineering & Physics, Lesson 5.3 (grade 6)

displaceEnglish
To push aside. A boat pushes water out of the way to make room for itself.
Grade 2 Engineering & Physics, Lesson 6.1 (grade 2) · Grade 3 Engineering & Physics, Lesson 6.1 (grade 3) · Grade 4 Engineering & Physics, Lesson 6.1 (grade 4) · +1 more

distortionEnglish
The bending, bowing or shrinking of parts caused by the weld metal shrinking as it cools.
Shop & Trades, Lesson 7.4 (grade 9–12) · Explore Travel and Faraway Places · Expert, Stop 1.1 (Ages 14+) · Explore Travel and Faraway Places · Ranger, Stop 1.1 (Ages 10–13) · +1 more

diversion tunnelEnglish
A tunnel that carries a river around the place where a dam is being built.
Grade 4 Engineering & Physics, Lesson 5.3 (grade 4)

door swingEnglish
A quarter-circle arc drawn on the plan showing which way a door opens and the space it needs.
Architecture & Civil Engineering, Lesson 2.2 (grade 9–12)

dopingEnglish
Adding a tiny, controlled amount of impurity to a semiconductor: phosphorus or arsenic makes n-type (extra electrons); boron or gallium makes p-type (holes).
Electronics & Microcontrollers, Lesson 4.1 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 4.2 (grade 8)

Doppler effectEnglish
The change in observed frequency of a wave because the source or the observer is moving: higher when they approach each other, lower when they separate.
Physics, Lesson 9.3 (grade 11–12) · Technology Overcoming Geography, Lesson 5.1 (grade 9–12)

double bottomEnglish
A second watertight layer inside the bottom of a hull, so a hole in the outer layer does not flood the ship.
Grade 5 Engineering & Physics, Lesson 6.4 (grade 5)

double hullEnglish
A hull with an inner and an outer skin, so a hole in the outer skin need not let water inside the ship.
Grade 7 Engineering & Physics, Lesson 6.2 (grade 7)

double shearEnglish
A pin or bolt that is cut by two shear planes at once (as in a clevis) and so has twice the area resisting the load.
Engineering Design, Robotics & Drones, Lesson 5.1 (grade 9–12)

dovetailEnglish
A joint shaped like a bird’s tail that locks two pieces together.
Grade 3 Engineering & Physics, Lesson 6.4 (grade 3) · Shop & Trades, Lesson 3.4 (grade 9–12)

downwashEnglish
Air turned downward behind a wing.
Grade 6 Engineering & Physics, Lesson 7.1 (grade 6)

draft angleEnglish
A slight taper (often 1–2°) on walls parallel to the mold’s opening direction, so the part slides out without scraping.
Engineering Design, Robotics & Drones, Lesson 3.5 (grade 9–12) · Grade 7 Engineering & Physics, Lesson 9.4 (grade 7)

dragEnglish
The backward push of the air that slows a flying thing down.
Grade 2 Engineering & Physics, Lesson 7.1 (grade 2) · Grade 3 Engineering & Physics, Lesson 7.2 (grade 3) · Grade 4 Engineering & Physics, Lesson 7.1 (grade 4) · +3 more

draw-boreEnglish
Pegging a mortise and tenon through holes deliberately offset by about 1/16–1/8 in, so the peg pulls the joint tight and holds it even if the glue fails.
Shop & Trades, Lesson 3.4 (grade 9–12)

driftEnglish
How far a building sways sideways at its top under wind; often limited to about height/400 to height/500.
Architecture & Civil Engineering, Lesson 7.3 (grade 9–12) · Engineering Design, Robotics & Drones, Lesson 8.1 (grade 9–12) · Grade 6 Engineering & Physics, Lesson 7.3 (grade 6) · +2 more

driver and driven gearEnglish
The driver is turned by the motor or hand; the driven gear is turned by the driver.
Engineering Design, Robotics & Drones, Lesson 4.2 (grade 9–12)

driver gearEnglish
The gear that is turned by a hand, motor or crank and turns the others.
Grade 3 Engineering & Physics, Lesson 1.3 (grade 3)

drivetrainEnglish
The motors, gearboxes, wheels or tracks and frame that move a robot across the ground.
Engineering Design, Robotics & Drones, Lesson 6.2 (grade 9–12) · Shop & Trades, Lesson 10.1 (grade 9–12)

droneEnglish
A flying robot with no pilot on board. It is flown by remote control or by a program.
Grade 2 Engineering & Physics, Lesson 8.4 (grade 2) · Explore Animals · Ranger, Stop 5.2 (Ages 10–13) · Grade 1 Gardening & Animals, Lesson 6.4 (grade 1) · +3 more

drone (UAS)English
An uncrewed aircraft; the FAA calls the aircraft plus its controller an unmanned aircraft system.
Engineering Design, Robotics & Drones, Lesson 9.1 (grade 9–12)

drop testEnglish
Dropping a toy from a set height onto a hard surface to see whether it breaks into dangerous pieces.
Grade 6 Engineering & Physics, Lesson 9.4 (grade 6)

drumEnglish
The cylindrical wall on which a dome sits, often pierced with windows.
Architecture & Civil Engineering, Lesson 1.3 (grade 9–12)

drywall (gypsum board)English
Panels of gypsum plaster faced with paper, screwed to framing and finished with tape and joint compound; Type X board contains glass fibers for extra fire resistance.
Shop & Trades, Lesson 4.5 (grade 9–12)

duct leakageEnglish
Air lost through unsealed joints and seams; leaky ducts in attics or crawl spaces can lose 20–30 percent of the air a system moves.
Shop & Trades, Lesson 6.5 (grade 9–12)

ductile and brittleEnglish
A ductile material (steel) stretches and bends a great deal before breaking, giving warning; a brittle material (plain concrete, glass) breaks suddenly.
Grade 8 Engineering & Physics, Lesson 2.2 (grade 8)

ductile-to-brittle transitionEnglish
The temperature range below which some steels lose their toughness and break in a brittle way.
Grade 8 Engineering & Physics, Lesson 6.4 (grade 8)

ductilityEnglish
The ability to stretch a great deal before breaking, giving warning; steel is ductile, cast iron is brittle.
Architecture & Civil Engineering, Lesson 5.3 (grade 9–12)

ductility and toughnessEnglish
Ductility is how much a material can stretch permanently before breaking; toughness is how much energy it absorbs before breaking.
Engineering Design, Robotics & Drones, Lesson 3.1 (grade 9–12)

duty cycleEnglish
The fraction of each cycle that the output is high, as a percent.
Electronics & Microcontrollers, Lesson 5.3 (grade 9–12) · Electronics & Microcontrollers, Lesson 7.5 (grade 9–12) · Engineering Design, Robotics & Drones, Lesson 6.3 (grade 9–12)

duty_u16()English
Sets a Pico PWM duty cycle from 0 to 65535 (16 bits): 32768 is 50%.
Electronics & Microcontrollers, Lesson 9.5 (grade 9–12)

dynamoEnglish
An early name for an electric generator, especially one making direct current.
Grade 6 Engineering & Physics, Lesson 4.2 (grade 6)

edge pieceEnglish
One of the 12 cube pieces with two colored faces.
Grade 5 Engineering & Physics, Lesson 9.3 (grade 5) · Tactics & Strategy, Lesson 2.2 (grade 4–7)

effective stressEnglish
The stress carried grain to grain, \sigma′ = \sigma - u; it controls a soil’s strength and compression (Terzaghi’s principle).
Architecture & Civil Engineering, Lesson 8.1 (grade 9–12)

efficacyEnglish
Light output per electrical power, in lumens per watt (lm/W): about 14 for incandescent, 60–70 for compact fluorescent, 80–150 for LED.
Shop & Trades, Lesson 5.5 (grade 9–12)

efficiencyEnglish
Useful output power divided by input power, often as a percent.
Electronics & Microcontrollers, Lesson 1.4 (grade 9–12) · Engineering Design, Robotics & Drones, Lesson 1.1 (grade 9–12) · Engineering Design, Robotics & Drones, Lesson 4.1 (grade 9–12) · +3 more

ejector pinEnglish
A pin that pushes the cooled part out of the mold, leaving a small round mark.
Grade 7 Engineering & Physics, Lesson 9.4 (grade 7)

elastic collisionEnglish
A collision in which total kinetic energy is conserved (as well as momentum). Steel balls and billiard balls come close.
Physics, Lesson 6.3 (grade 11–12)

elastic limitEnglish
The point past which a spring is bent out of shape and will not spring back.
Grade 4 Engineering & Physics, Lesson 9.3 (grade 4) · Grade 7 Engineering & Physics, Lesson 3.1 (grade 7) · Physics, Lesson 1.4 (grade 11–12)

elastic potential energyEnglish
Energy stored in something that is stretched, squeezed or twisted, such as a spring or rubber band.
Grade 4 Engineering & Physics, Lesson 1.2 (grade 4) · Grade 4 Engineering & Physics, Lesson 9.3 (grade 4) · Grade 6 Engineering & Physics, Lesson 9.1 (grade 6) · +1 more

electric arcEnglish
A continuous spark: electric current flowing through hot, ionized gas between an electrode and the work, producing intense heat and light.
Shop & Trades, Lesson 7.1 (grade 9–12)

electric chargeEnglish
A basic property of matter that makes particles push or pull on each other. Electrons carry negative charge and protons positive. Unit: the coulomb (C).
Electronics & Microcontrollers, Lesson 1.1 (grade 9–12) · Physics, Lesson 10.1 (grade 11–12)

electric motorEnglish
A machine that uses magnetic forces on electric currents to turn electrical energy into motion.
Grade 5 Engineering & Physics, Lesson 4.2 (grade 5)

electric powerEnglish
The rate of energy transfer, P = IV, in watts.
Physics, Lesson 10.2 (grade 11–12)

electricianEnglish
A trained worker who safely puts in and fixes the wires in a building.
Kindergarten Engineering & Physics, Lesson 4.4 (grade K)

electrolytic capacitorEnglish
A capacitor with large capacitance in a small can. It is polarized: the stripe marks the negative lead, and it must never be connected backward or above its voltage rating.
Electronics & Microcontrollers, Lesson 3.2 (grade 9–12)

electromagnetEnglish
A magnet made by electricity flowing through a coil of wire. It turns off when the electricity stops.
Grade 2 Engineering & Physics, Lesson 4.4 (grade 2) · Grade 3 Engineering & Physics, Lesson 4.4 (grade 3) · Grade 4 Engineering & Physics, Lesson 4.2 (grade 4) · +2 more

electromagnetic inductionEnglish
Making an electric current in a wire by moving a magnet near it, or moving the wire near a magnet.
Grade 5 Engineering & Physics, Lesson 5.3 (grade 5) · Grade 6 Engineering & Physics, Lesson 4.3 (grade 6) · Physics, Lesson 10.4 (grade 11–12)

electromagnetic spectrumEnglish
The full range of electromagnetic waves: radio, microwaves, infrared, visible light (about 400–700 nm), ultraviolet, X-rays and gamma rays.
Physics, Lesson 10.5 (grade 11–12)

electromagnetic waveEnglish
A wave of electric and magnetic fields that travels at the speed of light, c = 3.0 \times 10^8\ \text{m/s}: radio, infrared, light and more.
Electronics & Microcontrollers, Lesson 10.2 (grade 9–12) · Grade 7 Engineering & Physics, Lesson 5.4 (grade 7) · Physics, Lesson 10.5 (grade 11–12)

electromechanical (EM)English
Machines that use switches, relays, motors and spinning score reels instead of computer chips to keep track of a game.
Grade 7 Engineering & Physics, Lesson 9.1 (grade 7)

electromotive force (emf)English
The voltage a source such as a battery or generator produces when no current is drawn. The name is old; it is an energy per charge, not a force.
Electronics & Microcontrollers, Lesson 1.2 (grade 9–12)

electronic speed controller (ESC)English
The driver that turns the flight controller’s commands into rapidly switched currents for a brushless motor.
Engineering Design, Robotics & Drones, Lesson 9.3 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 9.3 (grade 8)

elementary chargeEnglish
The charge of one proton, e = 1.602 \times 10^{-19}\ \text{C}; an electron has -e. All free charges are whole multiples of e.
Physics, Lesson 10.1 (grade 11–12)

elevatorEnglish
A box or platform that carries people or things up and down inside a building.
Grade 2 Engineering & Physics, Lesson 3.4 (grade 2) · Grade 2 Engineering & Physics, Lesson 7.3 (grade 2)

enclosureEnglish
The case that protects a circuit and the user: it holds the board and battery and exposes only the switch, light or controls.
Electronics & Microcontrollers, Lesson 5.5 (grade 9–12)

end effectorEnglish
The tool at the end of a robot arm that does the work: a gripper, suction cup, welding torch, snare or hand.
Grade 7 Engineering & Physics, Lesson 8.1 (grade 7)

endurance limitEnglish
For steels, a stress below which fatigue failure does not occur however many cycles are applied; aluminum alloys have none.
Engineering Design, Robotics & Drones, Lesson 5.4 (grade 9–12)

energy lossEnglish
Energy turned into heat and sound in each bounce, which must be replaced to keep going.
Grade 4 Engineering & Physics, Lesson 9.3 (grade 4) · Grade 6 Engineering & Physics, Lesson 9.1 (grade 6)

energy transferEnglish
When energy passes from one object to another, like a rolling ball knocking over a domino.
Grade 4 Engineering & Physics, Lesson 1.4 (grade 4)

engineEnglish
A machine that makes power to turn the propellers.
Kindergarten Engineering & Physics, Lesson 7.4 (grade K) · Kindergarten Geography: God Made the Earth: My First Maps, Lesson 8.3 (grade K)

engineer of recordEnglish
The licensed engineer whose seal is on the structural design and who is responsible for it.
Grade 8 Engineering & Physics, Lesson 8.1 (grade 8)

engineeringEnglish
The creative use of science, mathematics and experience to design things that meet human needs within real limits of cost, safety, materials and time.
Engineering Design, Robotics & Drones, Lesson 1.1 (grade 9–12)

engineering design processEnglish
A repeating cycle engineers use: define the problem, research, write requirements, generate ideas, choose a concept, build a prototype, test, and improve, then communicate the result.
Engineering Design, Robotics & Drones, Lesson 1.1 (grade 9–12) · Grade 1 Engineering & Physics, Lesson 8.4 (grade 1) · Grade 3 Engineering & Physics, Lesson 8.4 (grade 3) · +2 more

engineering fairEnglish
A show where engineers display what they built and explain how it works.
Grade 2 Engineering & Physics, Lesson 8.4 (grade 2)

engineering prefixesEnglish
Multipliers used for convenient numbers: m (milli, 10^{-3}), µ (micro, 10^{-6}), k (kilo, 10^{3}), M (mega, 10^{6}).
Electronics & Microcontrollers, Lesson 1.3 (grade 9–12)

engineering reportEnglish
A written record of a project with a standard structure: summary, problem, requirements, design, testing, results, conclusions and recommendations.
Grade 8 Engineering & Physics, Lesson 8.4 (grade 8)

engineer’s notebookEnglish
A bound, page-numbered record of a design’s life, written in ink and dated, containing ideas, sketches, calculations, test data, decisions and reflections.
Engineering Design, Robotics & Drones, Lesson 1.5 (grade 9–12) · Grade 5 Engineering & Physics, Lesson 1.1 (grade 5)

engineer’s scaleEnglish
A scale divided into 10, 20, 30, 40, 50 or 60 parts per inch, used for site plans and civil drawings (for example 1″ = 20′).
Architecture & Civil Engineering, Lesson 2.1 (grade 9–12)

entablatureEnglish
The horizontal band carried by classical columns: architrave (the stone beam), frieze and cornice.
Grade 8 Engineering & Physics, Lesson 3.1 (grade 8)

entasisEnglish
The slight outward swelling of a column’s shaft, a visual refinement used by Greek builders.
Architecture & Civil Engineering, Lesson 3.1 (grade 9–12)

EPA Section 608English
The U.S. rule under the Clean Air Act that requires technicians who service or dispose of equipment with refrigerant to be certified, and forbids knowingly venting refrigerant.
Shop & Trades, Lesson 6.3 (grade 9–12)

epoxy resinEnglish
A liquid whose molecules end in reactive three-membered epoxide rings.
Shop & Trades, Lesson 2.3 (grade 9–12)

equilibrium moisture content (EMC)English
The moisture content wood settles at in a given temperature and humidity; about 6–8% in a heated house in winter and around 12% outdoors in much of the United States.
Shop & Trades, Lesson 3.1 (grade 9–12)

equipment grounding conductorEnglish
The bare or green wire that bonds metal boxes, appliance cases and the receptacle ground pin back to the panel. It carries current only during a fault, so that the breaker trips fast.
Shop & Trades, Lesson 5.3 (grade 9–12)

equivalent resistanceEnglish
The single resistance that would draw the same current from the source as a whole network of resistors.
Electronics & Microcontrollers, Lesson 2.1 (grade 9–12)

ESALEnglish
Equivalent single-axle load: the number of standard 18,000 lb axle passes that would do the same damage as a given traffic mix.
Architecture & Civil Engineering, Lesson 9.4 (grade 9–12)

escalationEnglish
The expected rise in construction prices between the estimate and the time of building.
Architecture & Civil Engineering, Lesson 10.4 (grade 9–12)

escape speedEnglish
The launch speed needed to leave a planet’s gravity entirely (ignoring air): v_{\text{esc}} = \sqrt{2GM/r}, 11.2 km/s from the Earth’s surface.
Physics, Lesson 4.5 (grade 11–12)

escapementEnglish
The part of a clock that lets the gears move forward one tooth at a time with each swing of the pendulum.
Grade 5 Engineering & Physics, Lesson 1.4 (grade 5) · Physics, Lesson 9.1 (grade 11–12)

E-series (preferred values)English
Standard resistor values spaced so that each is about the same percentage above the last. E12 (for ±10%): 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2, times any power of ten.
Electronics & Microcontrollers, Lesson 3.1 (grade 9–12)

Euler buckling loadEnglish
P_{cr} = \dfrac{\pi^2 EI}{(KL)^2}, the load at which a slender column buckles; it falls with the square of the unbraced length.
Architecture & Civil Engineering, Lesson 6.4 (grade 9–12)

evaporative finishEnglish
A finish that cures only by its solvent evaporating, such as shellac (alcohol) and lacquer; later coats redissolve earlier ones, so they melt together and are easy to repair.
Shop & Trades, Lesson 3.5 (grade 9–12)

evaporatorEnglish
The indoor coil where the cold, low-pressure refrigerant boils, absorbing heat (and condensing moisture) from house air.
Shop & Trades, Lesson 6.3 (grade 9–12)

exhaust velocityEnglish
How fast the hot gases leave the nozzle. Higher exhaust velocity means more push from each kilogram of propellant.
Grade 8 Engineering & Physics, Lesson 7.3 (grade 8) · Physics, Lesson 6.4 (grade 11–12)

exothermEnglish
Heat released by a chemical reaction; in epoxy, the heat speeds the reaction, which releases more heat.
Shop & Trades, Lesson 2.3 (grade 9–12)

exploded viewEnglish
A drawing of an assembly with parts pulled apart along their assembly directions to show how they go together.
Engineering Design, Robotics & Drones, Lesson 2.5 (grade 9–12)

extensionEnglish
How much a spring’s length has increased from its relaxed length.
Physics, Lesson 1.4 (grade 11–12) · Home Décor, Costume & Upholstery, Lesson 3.1 (grade 9–12)

extruderEnglish
The mechanism (gears driven by a motor) that grips the filament and pushes it into the hot end at a measured rate.
Shop & Trades, Lesson 8.2 (grade 9–12)

eyebarEnglish
A flat steel bar with a large hole (an “eye”) at each end, pinned to other eyebars to form a chain.
Grade 6 Engineering & Physics, Lesson 2.4 (grade 6)

eyebar chainEnglish
A chain made of flat bars with holes (eyes) at each end, linked by pins, used for early suspension bridges.
Architecture & Civil Engineering, Lesson 6.2 (grade 9–12)

FAAEnglish
The Federal Aviation Administration, the U.S. agency that makes the rules for everything that flies, including drones.
Grade 5 Engineering & Physics, Lesson 7.4 (grade 5)

factor of safetyEnglish
The ratio of what a part can carry to what it must carry: FS = \text{capacity} / \text{demand}.
Architecture & Civil Engineering, Lesson 1.4 (grade 9–12)

factor of safety against sliding and overturningEnglish
Resisting force (or moment) divided by driving force (or moment); typically at least 1.5 for sliding and 2.0 for overturning.
Architecture & Civil Engineering, Lesson 8.4 (grade 9–12)

factor of safety (FOS)English
Strength (failure load or stress) divided by the actual working load or stress; how many times stronger a part is than it needs to be.
Engineering Design, Robotics & Drones, Lesson 5.2 (grade 9–12)

fail-safeEnglish
Designed so that if something breaks, the machine stops in a safe way instead of a dangerous one.
Grade 5 Engineering & Physics, Lesson 3.3 (grade 5) · Grade 8 Engineering & Physics, Lesson 6.3 (grade 8)

failure modeEnglish
How a joint breaks: adhesive failure (at the interface), cohesive failure (within the glue) or substrate failure (the material itself breaks).
Shop & Trades, Lesson 2.1 (grade 9–12)

failure reviewEnglish
A structured meeting to study a failure honestly, without blame, to learn and prevent it.
Engineering Design, Robotics & Drones, Lesson 10.4 (grade 9–12)

fall (slope)English
The downhill pitch of a drain pipe, usually ¼ in per foot for small drains, so waste flows without standing or separating.
Shop & Trades, Lesson 4.5 (grade 9–12)

falseworkEnglish
Temporary supports used to hold a bridge up until it can carry itself.
Architecture & Civil Engineering, Lesson 6.1 (grade 9–12)

Faraday cageEnglish
A conducting enclosure that blocks electric fields and radio waves from getting in or out.
Grade 7 Engineering & Physics, Lesson 5.4 (grade 7)

Faraday’s lawEnglish
The induced emf equals the rate of change of flux linkage: \mathcal{E} = -N\dfrac{\Delta\Phi}{\Delta t}.
Physics, Lesson 10.4 (grade 11–12)

fast-track constructionEnglish
Overlapping design and construction so that work begins before every drawing is finished, as at the Empire State Building.
Architecture & Civil Engineering, Lesson 7.4 (grade 9–12)

fatigueEnglish
Failure of a material under repeated loading at stresses well below its static strength, by a crack that grows a little with each cycle.
Engineering Design, Robotics & Drones, Lesson 5.4 (grade 9–12) · Grade 6 Engineering & Physics, Lesson 2.4 (grade 6) · Grade 8 Engineering & Physics, Lesson 2.4 (grade 8) · +1 more

FCAW (flux-core)English
Flux-cored arc welding: like MIG but the wire is a tube filled with flux. Self-shielded wire needs no gas and works outdoors; it leaves slag.
Shop & Trades, Lesson 7.3 (grade 9–12)

FDMEnglish
Fused deposition modeling: a printer melts plastic filament and lays it down through a moving nozzle, one layer at a time.
Engineering Design, Robotics & Drones, Lesson 3.4 (grade 9–12)

featherEnglish
The light covering on a bird. Long, stiff feathers on the wings push on the air.
Kindergarten Engineering & Physics, Lesson 7.1 (grade K) · Explore Dinosaurs, Stop 3.7 (Ages 7–9) · Explore Horses and Ponies · Expert, Stop 1.4 (Ages 14+) · +3 more

feature treeEnglish
The ordered list of sketches and features that build a part; editing an early step updates every later one.
Engineering Design, Robotics & Drones, Lesson 2.4 (grade 9–12)

feedback (closed loop)English
Measuring the result and correcting toward the goal: the servo compares its actual angle with the commanded one and drives the motor to reduce the difference.
Electronics & Microcontrollers, Lesson 8.2 (grade 9–12)

feedback (closed-loop) controlEnglish
Control that measures the result and keeps adjusting to reach the goal.
Grade 7 Engineering & Physics, Lesson 8.2 (grade 7)

feedback controlEnglish
A loop in which a sensor measures what is happening, a controller compares it with what is wanted, and the motors correct the difference.
Grade 8 Engineering & Physics, Lesson 7.4 (grade 8)

fetch–decode–executeEnglish
The cycle every CPU repeats: fetch the next instruction from memory, decode what it means, execute it, and move on.
Electronics & Microcontrollers, Lesson 6.5 (grade 9–12)

fidelityEnglish
How close a prototype is to the final product, from a rough low-fidelity mockup to a high-fidelity working model.
Engineering Design, Robotics & Drones, Lesson 1.4 (grade 9–12)

figure of meritEnglish
The ratio of ideal hover power to the actual power a rotor needs, typically about 0.5 to 0.75.
Engineering Design, Robotics & Drones, Lesson 9.2 (grade 9–12)

fillet weldEnglish
A roughly triangular weld in the corner of a lap, tee or corner joint. Its size is the leg length.
Shop & Trades, Lesson 7.4 (grade 9–12)

film finish and penetrating finishEnglish
A film finish (shellac, lacquer, varnish, polyurethane) builds a hard layer on top of the wood; a penetrating finish (linseed or tung oil, oil-varnish blends) soaks into the surface and leaves little or no film.
Shop & Trades, Lesson 3.5 (grade 9–12)

filterEnglish
Something that lets water pass through but catches dirt.
Grade 3 Engineering & Physics, Lesson 5.1 (grade 3) · Grade 1 Gardening & Animals, Lesson 4.2 (grade 1) · Grade 3 Gardening & Animals, Lesson 4.1 (grade 3) · +2 more

filter shadeEnglish
The darkness number of a welding lens. Most arc welding needs shade 10–13; gas welding and brazing need about shade 4–6.
Shop & Trades, Lesson 7.5 (grade 9–12)

filtrationEnglish
Passing water through sand, gravel or membranes to remove remaining particles; slow sand filters also grow a living layer that removes germs.
Architecture & Civil Engineering, Lesson 9.2 (grade 9–12) · Grade 5 Engineering & Physics, Lesson 5.1 (grade 5) · Grade 6 Engineering & Physics, Lesson 5.1 (grade 6) · +1 more

final reportEnglish
The written record of a project, complete enough for someone else to understand, check, build and improve it.
Engineering Design, Robotics & Drones, Lesson 10.5 (grade 9–12)

fireproofingEnglish
Protection (originally terra-cotta tile and masonry, now sprayed fiber, board or concrete) that keeps a steel frame from losing strength in a fire.
Architecture & Civil Engineering, Lesson 7.1 (grade 9–12)

fire-resistance ratingEnglish
The time (in hours) a wall, floor or column can withstand a standard fire test without collapse or letting fire through.
Architecture & Civil Engineering, Lesson 7.5 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 3.3 (grade 8)

firmitas (firmness)English
Structural soundness: the building stands, carries its loads safely and lasts.
Architecture & Civil Engineering, Lesson 1.1 (grade 9–12)

firmnessEnglish
Vitruvius’s firmitas: a building must stand strong and last.
Grade 6 Engineering & Physics, Lesson 3.2 (grade 6)

firmware (UF2)English
The MicroPython program itself, copied onto the Pico as a .uf2 file while BOOTSEL is held.
Electronics & Microcontrollers, Lesson 9.4 (grade 9–12)

FIRSTEnglish
For Inspiration and Recognition of Science and Technology, a nonprofit founded by Dean Kamen in 1989 that runs robotics competitions for students.
Engineering Design, Robotics & Drones, Lesson 6.5 (grade 9–12)

first law of thermodynamicsEnglish
Energy is conserved: the change in a system’s internal energy equals the heat added minus the work done by the system, \Delta U = Q - W.
Physics, Lesson 8.5 (grade 11–12)

first-angle projectionEnglish
The arrangement used in most of Europe and Asia: the top view is drawn below the front view and the right-side view to its left.
Engineering Design, Robotics & Drones, Lesson 2.2 (grade 9–12)

fishbone (Ishikawa) diagramEnglish
A chart that sorts possible causes of a problem into categories (people, methods, materials, machines, measurement, environment).
Engineering Design, Robotics & Drones, Lesson 10.4 (grade 9–12)

five basic jointsEnglish
Butt (edge to edge in one plane), lap (overlapping), tee (one piece square to another), corner (an L at the edges) and edge (two edges side by side).
Shop & Trades, Lesson 7.4 (grade 9–12)

fixed pulleyEnglish
A pulley that stays in one place. It changes the direction of your pull.
Grade 3 Engineering & Physics, Lesson 1.2 (grade 3)

flangeEnglish
The top or bottom plate of an I-beam or box girder, which carries most of the compression or tension.
Grade 6 Engineering & Physics, Lesson 2.1 (grade 6) · Grade 4 Geography: The United States: Regions, Rivers and Routes, Lesson 7.1 (grade 4)

flashingEnglish
Thin metal (or membrane) pieces that turn water at joints and edges: drip edge at eaves and rakes, step flashing where a roof meets a wall, valley flashing, and boots around pipes.
Shop & Trades, Lesson 4.3 (grade 9–12)

flat-sawn and quartersawnEnglish
A flat-sawn board has growth rings running roughly across its width; a quartersawn board has rings running roughly up and down through its thickness, so it shrinks and swells less across its width.
Shop & Trades, Lesson 3.1 (grade 9–12)

flesh-sensing brakeEnglish
A table-saw safety system (SawStop) that detects skin touching the blade by a change in an electrical signal and stops the blade in a few thousandths of a second.
Shop & Trades, Lesson 3.3 (grade 9–12)

flexible and rigid pavementsEnglish
Asphalt pavements flex and spread load through their layers; concrete pavements are stiff slabs that bridge over weak spots.
Architecture & Civil Engineering, Lesson 9.4 (grade 9–12)

flight controllerEnglish
The small computer that reads the IMU many times a second and adjusts each motor’s speed to keep the drone stable.
Grade 7 Engineering & Physics, Lesson 8.4 (grade 7)

flight logEnglish
A record of each flight: date, place, drone, duration, battery, conditions and any problems.
Engineering Design, Robotics & Drones, Lesson 9.5 (grade 9–12)

flight simulatorEnglish
A machine or program that reproduces the experience of flying so that pilots can practice safely and repeatedly.
Engineering Design, Robotics & Drones, Lesson 9.5 (grade 9–12)

flip-flopEnglish
A clocked memory element. A D flip-flop copies its D input to its output Q at the moment the clock rises (the rising edge) and holds it until the next edge.
Electronics & Microcontrollers, Lesson 6.4 (grade 9–12)

float bowlEnglish
A small fuel reservoir under the carburetor whose float and needle valve keep the fuel at a constant level.
Shop & Trades, Lesson 9.3 (grade 9–12)

float (slack)English
How long a task not on the critical path can be delayed without delaying the project.
Grade 8 Engineering & Physics, Lesson 8.2 (grade 8)

float valveEnglish
A valve opened and closed by a floating ball or cup, which keeps water at a set level.
Grade 4 Engineering & Physics, Lesson 8.3 (grade 4)

floating inputEnglish
An input connected to nothing; it picks up stray charge and reads randomly.
Electronics & Microcontrollers, Lesson 7.3 (grade 9–12)

flocculationEnglish
Gentle, slow stirring that lets the sticky particles collect into larger clumps called floc.
Grade 6 Engineering & Physics, Lesson 5.1 (grade 6)

floorEnglish
One level of a building. A skyscraper has floors stacked one on top of another.
Kindergarten Engineering & Physics, Lesson 3.3 (grade K)

floor area ratio (FAR)English
Gross floor area divided by lot area; a zoning limit on how much building a lot may hold.
Architecture & Civil Engineering, Lesson 10.2 (grade 9–12)

flow, density and speedEnglish
Flow q (vehicles per hour), density k (vehicles per kilometer per lane), and speed v, linked by q = kv.
Architecture & Civil Engineering, Lesson 9.5 (grade 9–12)

flow rate (Q)English
The volume of water passing per second, in cubic meters per second (m³/s).
Grade 7 Engineering & Physics, Lesson 5.2 (grade 7)

flue and draftEnglish
The flue (vent) carries combustion gases outdoors; draft is the pressure difference that moves them, from rising hot gases (natural draft) or a fan (induced draft).
Shop & Trades, Lesson 6.2 (grade 9–12)

flutterEnglish
A dangerous motion in which a structure’s own twisting changes how the wind pushes on it, so the wind feeds the twisting.
Grade 5 Engineering & Physics, Lesson 2.4 (grade 5)

fluxEnglish
A chemical (usually rosin, inside the solder’s core) that cleans oxide from metal surfaces as they heat, so the solder can wet them.
Electronics & Microcontrollers, Lesson 5.2 (grade 9–12) · Grade 7 Engineering & Physics, Lesson 4.4 (grade 7) · Shop & Trades, Lesson 7.1 (grade 9–12)

flyback diodeEnglish
A diode across a coil, pointing backward to the supply, that gives the coil’s current a safe path when it is switched off and stops a damaging voltage spike.
Electronics & Microcontrollers, Lesson 3.3 (grade 9–12)

flying discEnglish
A spinning, saucer-shaped toy that flies by making lift, like a round wing.
Grade 5 Engineering & Physics, Lesson 9.1 (grade 5)

flywheelEnglish
A heavy wheel with large rotational inertia, used to smooth out rotation or store energy.
Physics, Lesson 7.4 (grade 11–12)

FMEAEnglish
Failure modes and effects analysis: a systematic list of the ways each part could fail, their effects, and how to prevent or detect them.
Engineering Design, Robotics & Drones, Lesson 8.5 (grade 9–12)

follower gearEnglish
A gear that is turned by another gear.
Grade 3 Engineering & Physics, Lesson 1.3 (grade 3)

for loopEnglish
Repeats a block of code a set number of times: for (int i = 0; i < 5; i++) { … } runs it 5 times.
Electronics & Microcontrollers, Lesson 7.2 (grade 9–12)

force pairEnglish
The two forces of a third-law interaction. They act on different objects, are the same kind of force and are equal and opposite.
Physics, Lesson 3.1 (grade 11–12)

forge weldingEnglish
The oldest kind of welding: heating iron or steel nearly to melting in a forge and hammering the pieces together so the metal bonds in the solid state.
Shop & Trades, Lesson 7.1 (grade 9–12)

formative manufacturingEnglish
Making a part by forcing material into shape: casting, molding, forging, stamping.
Shop & Trades, Lesson 8.1 (grade 9–12)

forward voltageEnglish
The voltage a conducting diode drops: about 0.6–0.7 V for silicon, 0.2–0.4 V for Schottky diodes, 1.8–3.3 V for LEDs.
Electronics & Microcontrollers, Lesson 3.4 (grade 9–12)

forward voltage (VF)English
The voltage across a lit LED: about 1.8–2.2 V for red, yellow and some green; about 2.8–3.4 V for blue, white and true green.
Electronics & Microcontrollers, Lesson 3.5 (grade 9–12)

four forces of flightEnglish
Lift (up), weight (down), thrust (forward) and drag (backward).
Grade 5 Engineering & Physics, Lesson 7.3 (grade 5)

four-bar linkageEnglish
The simplest movable closed linkage: a fixed frame, an input crank, a coupler and an output link.
Engineering Design, Robotics & Drones, Lesson 4.3 (grade 9–12)

four-stroke cycleEnglish
Intake, compression, power and exhaust: the four piston movements that make one full cycle of most car engines.
Grade 7 Engineering & Physics, Lesson 1.3 (grade 7) · Shop & Trades, Lesson 9.1 (grade 9–12)

fracture-critical memberEnglish
A steel part in tension whose failure would cause the bridge to collapse.
Grade 6 Engineering & Physics, Lesson 2.4 (grade 6) · Grade 8 Engineering & Physics, Lesson 2.4 (grade 8)

frame constructionEnglish
A building whose floors and walls are carried by a framework of columns and beams; the exterior wall is hung on the frame.
Architecture & Civil Engineering, Lesson 7.1 (grade 9–12)

frame structureEnglish
A structure of columns and beams (steel or reinforced concrete) that carries all the loads, so walls need not.
Architecture & Civil Engineering, Lesson 3.5 (grade 9–12)

framed tubeEnglish
A building whose closely spaced exterior columns and deep spandrel beams form a stiff hollow tube that resists wind like a giant hollow beam.
Architecture & Civil Engineering, Lesson 7.3 (grade 9–12)

free fallEnglish
Motion under the influence of gravity alone, with no significant air resistance. An object in free fall accelerates at g downward whether it is moving up, down or sideways.
Physics, Lesson 2.3 (grade 11–12)

free (no-load) speedEnglish
The speed a motor reaches with nothing attached; the maximum speed, at nearly zero torque.
Engineering Design, Robotics & Drones, Lesson 4.5 (grade 9–12)

free planEnglish
A plan in which interior walls can go anywhere, because columns, not walls, carry the floors.
Architecture & Civil Engineering, Lesson 3.5 (grade 9–12)

freeboardEnglish
The height of a ship’s side above the water, from the waterline to the deck.
Grade 4 Engineering & Physics, Lesson 6.2 (grade 4) · Grade 6 Engineering & Physics, Lesson 6.1 (grade 6) · Grade 7 Engineering & Physics, Lesson 6.2 (grade 7)

free-body diagramEnglish
A sketch of one body, cut free from its surroundings, with every force acting on it drawn as an arrow.
Architecture & Civil Engineering, Lesson 4.2 (grade 9–12) · Grade 7 Engineering & Physics, Lesson 2.1 (grade 7) · Physics, Lesson 3.3 (grade 11–12)

free-body diagram (extended object)English
A diagram of an object showing each force acting at its actual point of application, needed for torque calculations.
Physics, Lesson 7.3 (grade 11–12)

frequencyEnglish
How many waves pass each second, measured in hertz (Hz); 1 gigahertz (GHz) is a billion hertz.
Grade 6 Engineering & Physics, Lesson 9.3 (grade 6) · Grade 8 Engineering & Physics, Lesson 5.1 (grade 8) · Physics, Lesson 9.1 (grade 11–12) · +3 more

frequency (f)English
How many waves pass each second, measured in hertz (Hz). 1 MHz is a million hertz; 1 GHz is a billion.
Grade 7 Engineering & Physics, Lesson 5.4 (grade 7)

Fresnel lensEnglish
A lighthouse lens made of many rings of glass that bend light into a strong beam. (Say “fray-NEL.”)
Grade 3 Engineering & Physics, Lesson 6.4 (grade 3)

frictionEnglish
The rubbing that slows things down when two surfaces slide against each other.
Grade 1 Engineering & Physics, Lesson 1.2 (grade 1) · Grade 2 Engineering & Physics, Lesson 1.1 (grade 2) · Grade 3 Engineering & Physics, Lesson 1.1 (grade 3) · +3 more

friction and dragEnglish
Forces that oppose motion and turn mechanical energy into heat and sound.
Grade 7 Engineering & Physics, Lesson 1.4 (grade 7)

friction (skin) dragEnglish
Resistance from water rubbing along the wetted surface of the hull. It grows with wetted area and roughly with speed squared.
Grade 8 Engineering & Physics, Lesson 6.1 (grade 8)

fringeEnglish
One of the bright or dark bands in an interference pattern.
Physics, Lesson 9.5 (grade 11–12) · Explore Crafts and Making, Stop 2.4 (Ages 7–9) · Threads & Weaving, Lesson 2.4 (grade 9–12) · +2 more

Froebel giftsEnglish
Sets of wooden blocks, balls and tablets designed by the German educator Friedrich Froebel for the first kindergartens (1830s–1840s), used to teach form, proportion and composition.
Architecture & Civil Engineering, Lesson 2.5 (grade 9–12)

frost heaveEnglish
The upward push of soil when water in it freezes into growing ice lenses, which can lift and crack shallow foundations.
Shop & Trades, Lesson 4.1 (grade 9–12)

frost lineEnglish
The depth to which the ground freezes in winter in a given place. Footings are set below it so frost cannot heave them.
Shop & Trades, Lesson 4.1 (grade 9–12)

Froude numberEnglish
Fr = v ÷ √(gL). A model and a full-size ship at the same Froude number make the same pattern of waves.
Grade 8 Engineering & Physics, Lesson 6.1 (grade 8) · Explore Dinosaurs · Expert, Stop 3.5 (Ages 14+)

FTC and FRCEnglish
FIRST Tech Challenge (grades 7–12, smaller robots built from kit parts) and FIRST Robotics Competition (grades 9–12, large robots, a six-week build season).
Engineering Design, Robotics & Drones, Lesson 6.5 (grade 9–12)

fuel stabilizerEnglish
An additive that slows the oxidation of gasoline during storage.
Shop & Trades, Lesson 9.5 (grade 9–12)

fumeEnglish
Tiny particles of metal oxide formed when metal boils in the arc; zinc from galvanized steel causes metal fume fever, and stainless and chrome plating give off hexavalent chromium.
Shop & Trades, Lesson 7.5 (grade 9–12)

funicular shapeEnglish
The shape a cable or chain takes under a given set of loads; inverted, it is an arch in pure compression for those loads.
Architecture & Civil Engineering, Lesson 4.4 (grade 9–12)

fuse or circuit breakerEnglish
A device that opens a circuit when the current is too high, protecting wires and parts from overheating and fire.
Engineering Design, Robotics & Drones, Lesson 6.4 (grade 9–12)

fused deposition modeling (FDM)English
Scott Crump’s process: a plastic filament is melted and pushed through a nozzle that traces each layer; also called fused filament fabrication (FFF).
Shop & Trades, Lesson 8.1 (grade 9–12)

fusion zoneEnglish
The part of the joint that melted and froze again: weld metal made of filler and melted base metal.
Shop & Trades, Lesson 7.2 (grade 9–12)

gEnglish
A unit of acceleration equal to the pull of gravity, about 9.8 m/s². An accelerometer lying still reads 1 g upward.
Grade 7 Engineering & Physics, Lesson 9.3 (grade 7)

galvanic corrosionEnglish
Faster corrosion of the more active metal when two different metals touch in the presence of moisture.
Shop & Trades, Lesson 1.4 (grade 9–12)

galvanometerEnglish
A sensitive instrument that shows a small current by the deflection of a needle or coil in a magnetic field.
Electronics & Microcontrollers, Lesson 1.5 (grade 9–12) · Grade 6 Engineering & Physics, Lesson 4.3 (grade 6)

Gantt chartEnglish
A bar chart of tasks against time, showing when each starts and ends. It was developed by Henry Gantt in the 1910s.
Grade 8 Engineering & Physics, Lesson 8.2 (grade 8)

gateEnglish
A large door at each end of a lock that holds back water.
Grade 4 Engineering & Physics, Lesson 6.4 (grade 4) · Grade 4 Geography: The United States: Regions, Rivers and Routes, Lesson 6.2 (grade 4)

gate, drain, sourceEnglish
The MOSFET’s terminals: the gate controls; current flows from drain to source in an N-channel device.
Electronics & Microcontrollers, Lesson 4.4 (grade 9–12)

Gatun LakeEnglish
The large artificial lake, 26 meters above the sea, made by damming the Chagres River; ships cross Panama on it.
Grade 7 Engineering & Physics, Lesson 6.3 (grade 7)

gauge (go/no-go)English
A simple tool that checks whether a part is within tolerance: the “go” end must fit, the “no-go” end must not.
Engineering Design, Robotics & Drones, Lesson 3.3 (grade 9–12)

G-codeEnglish
The plain-text list of commands a printer follows: moves (G1 X Y Z E F), temperatures (M104, M140) and settings.
Shop & Trades, Lesson 8.2 (grade 9–12)

gearEnglish
A wheel with teeth that turns another wheel with teeth.
Grade 2 Engineering & Physics, Lesson 8.1 (grade 2) · Grade 3 Engineering & Physics, Lesson 1.3 (grade 3) · Grade 5 Engineering & Physics, Lesson 1.4 (grade 5)

gear ratioEnglish
The number of teeth on the driven gear divided by the number on the driving gear; it tells how many times the input turns for one turn of the output.
Engineering Design, Robotics & Drones, Lesson 4.2 (grade 9–12) · Grade 5 Engineering & Physics, Lesson 1.4 (grade 5) · Grade 6 Engineering & Physics, Lesson 8.1 (grade 6)

gear reductionEnglish
A gear train that makes the output turn slower but with more torque than the motor.
Grade 6 Engineering & Physics, Lesson 8.1 (grade 6)

gear trainEnglish
A row of gears that pass motion from one to the next.
Grade 3 Engineering & Physics, Lesson 1.3 (grade 3) · Grade 6 Engineering & Physics, Lesson 9.1 (grade 6)

generatorEnglish
A machine that makes electricity when its magnets and wires are turned around and around.
Grade 1 Engineering & Physics, Lesson 5.2 (grade 1) · Grade 2 Engineering & Physics, Lesson 5.3 (grade 2) · Grade 3 Engineering & Physics, Lesson 5.3 (grade 3) · +3 more

gentleEnglish
Slanting up slowly, like a long, low ramp.
Grade 1 Engineering & Physics, Lesson 1.3 (grade 1) · Kindergarten Gardening & Animals, Lesson 4.4 (grade K)

geostationary orbitEnglish
A circular orbit above the equator with a period of one sidereal day, so a satellite stays over the same spot on the ground.
Physics, Lesson 4.5 (grade 11–12) · Technology Overcoming Geography, Lesson 5.1 (grade 9–12)

geotechnical engineerEnglish
An engineer who studies soil and rock and designs foundations, tunnels and earthworks.
Grade 7 Engineering & Physics, Lesson 3.3 (grade 7)

geotechnical engineeringEnglish
The branch of civil engineering that studies soil and rock and designs foundations, slopes, retaining walls, tunnels and earth dams.
Architecture & Civil Engineering, Lesson 8.1 (grade 9–12)

GFCIEnglish
Ground-fault circuit interrupter. It compares the current going out on the hot with the current returning on the neutral and opens the circuit if they differ by about 4–6 mA.
Shop & Trades, Lesson 5.3 (grade 9–12)

g-forceEnglish
An acceleration expressed as a multiple of g (9.8 m/s²). Riders feel g-forces as being pressed into or lifted out of their seats.
Grade 8 Engineering & Physics, Lesson 1.4 (grade 8) · Physics, Lesson 2.2 (grade 11–12)

girderEnglish
A long, strong beam of steel used in buildings, bridges and towers.
Grade 3 Engineering & Physics, Lesson 9.4 (grade 3)

glancing collisionEnglish
A collision that is not head-on, so the objects move off at angles to the original direction.
Physics, Lesson 6.5 (grade 11–12)

glass transition temperatureEnglish
The temperature at which a rigid plastic softens and begins to sag under load: about 55–60 °C for PLA, 80 °C for PETG, 100–105 °C for ABS and ASA.
Shop & Trades, Lesson 8.5 (grade 9–12)

glideEnglish
To fly smoothly without flapping.
Kindergarten Engineering & Physics, Lesson 7.1 (grade K)

glide ratioEnglish
How far a glider travels forward for each unit it drops: distance ÷ height.
Grade 5 Engineering & Physics, Lesson 7.3 (grade 5) · Grade 7 Engineering & Physics, Lesson 7.2 (grade 7) · Grade 6 Life Science: Animal Design and Behavior, Lesson 1.4 (grade 6)

gliderEnglish
A flying machine with wings but no engine. It glides slowly down through the air.
Grade 1 Engineering & Physics, Lesson 7.3 (grade 1) · Grade 2 Engineering & Physics, Lesson 7.1 (grade 2) · Grade 3 Engineering & Physics, Lesson 7.3 (grade 3) · +3 more

GMAW (MIG welding)English
Gas metal arc welding: a solid wire fed continuously through a gun is the electrode and filler, shielded by gas such as 75% argon / 25% CO₂. Fast and easy to learn; poor in wind.
Shop & Trades, Lesson 7.3 (grade 9–12)

governorEnglish
A speed-sensing device that trips the safety brake if the car overspeeds.
Architecture & Civil Engineering, Lesson 7.2 (grade 9–12) · Shop & Trades, Lesson 9.4 (grade 9–12) · Grade 5 Geography: Explorers, Navigators and Missionaries, Lesson 8.2 (grade 5)

GPIOEnglish
General-purpose input/output: pins that software can set as inputs or outputs.
Electronics & Microcontrollers, Lesson 9.5 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 4.3 (grade 8)

GPS (GNSS)English
Satellite positioning: a receiver finds its position from the travel times of signals from at least four satellites.
Architecture & Civil Engineering, Lesson 9.1 (grade 9–12)

gracious professionalismEnglish
A FIRST value: competing hard while respecting and helping others.
Engineering Design, Robotics & Drones, Lesson 6.5 (grade 9–12)

gradingEnglish
Shaping the ground so water flows away from buildings, typically falling at least 6 in in the first 10 ft (5%).
Architecture & Civil Engineering, Lesson 10.2 (grade 9–12) · Explore Crafts and Making · Expert, Stop 1.7 (Ages 14+) · Textile Science & Clothing Construction, Lesson 8.5 (grade 9–12)

Grashof’s conditionEnglish
For a four-bar linkage with shortest link s, longest l and others p and q: if s + l ≤ p + q, at least one link can rotate fully.
Engineering Design, Robotics & Drones, Lesson 4.3 (grade 9–12)

gravitational constantEnglish
G = 6.674 \times 10^{-11}\ \text{N}\cdot\text{m}^{2}\text{/kg}^{2}, the same everywhere in the universe.
Physics, Lesson 4.2 (grade 11–12)

gravitational field strengthEnglish
The gravitational force per kilogram at a place, g = GM/r^2; at the Earth’s surface, 9.8\ \text{N/kg}.
Physics, Lesson 4.2 (grade 11–12)

gravitational potential energyEnglish
Energy stored by height: PE = m × g × h, where g ≈ 9.8 m/s².
Grade 7 Engineering & Physics, Lesson 1.4 (grade 7) · Physics, Lesson 5.3 (grade 11–12)

gravity and lateral systemsEnglish
The members that carry vertical loads (slabs, beams, columns, bearing walls) and those that carry sideways loads (braces, rigid frames, shear walls).
Architecture & Civil Engineering, Lesson 4.5 (grade 9–12)

gravity damEnglish
A dam that resists the water by its own weight, usually triangular in section.
Architecture & Civil Engineering, Lesson 8.5 (grade 9–12)

gravity wallEnglish
A retaining wall that resists the soil’s push by its own weight.
Architecture & Civil Engineering, Lesson 8.4 (grade 9–12)

gravity-fed systemEnglish
A water system in which water flows downhill from a higher source or tank to users without pumping.
Grade 8 Engineering & Physics, Lesson 5.2 (grade 8)

great circleEnglish
The shortest route between two points on a globe.
Grade 6 Engineering & Physics, Lesson 7.3 (grade 6) · Explore Travel and Faraway Places · Expert, Stop 1.1 (Ages 14+) · Geography and Commerce: Sea Lanes, Straits and Trade Routes, Lesson 2.5 (grade 9–12) · +3 more

gripperEnglish
The “hand” at the end of a robot arm that picks things up.
Grade 4 Engineering & Physics, Lesson 8.4 (grade 4) · Kindergarten Engineering & Physics, Lesson 8.3 (grade K)

gromaEnglish
A Roman surveying instrument: a cross on a staff with four plumb lines, used to sight straight lines and right angles.
Architecture & Civil Engineering, Lesson 9.1 (grade 9–12)

grossing factorEnglish
The ratio of gross building area to net program area, covering walls, halls, stairs and mechanical spaces; often 1.25–1.40.
Architecture & Civil Engineering, Lesson 10.1 (grade 9–12)

ground faultEnglish
Current leaving the circuit by an unintended path to ground: through a metal case, water, or a person.
Shop & Trades, Lesson 5.3 (grade 9–12)

ground symbolEnglish
A symbol marking the 0 V reference. Every ground symbol in a schematic is connected to every other.
Electronics & Microcontrollers, Lesson 2.4 (grade 9–12)

GTAW (TIG welding)English
Gas tungsten arc welding: a non-melting tungsten electrode makes the arc, argon shields it, and the welder adds filler rod by hand. Slow but precise and clean; best for thin metal, stainless and aluminum.
Shop & Trades, Lesson 7.3 (grade 9–12)

gussetEnglish
A plate (or card patch) that reinforces a joint where several members meet.
Architecture & Civil Engineering, Lesson 6.5 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 2.3 (grade 8)

gyrocompassEnglish
A compass made from a gyroscope that finds true north using the earth’s rotation instead of magnetism.
Grade 8 Engineering & Physics, Lesson 9.1 (grade 8)

gyroscopeEnglish
A spinning wheel mounted so that its axle can point in any direction; while it spins fast, it holds its direction.
Grade 3 Engineering & Physics, Lesson 9.3 (grade 3) · Grade 7 Engineering & Physics, Lesson 8.2 (grade 7) · Grade 7 Engineering & Physics, Lesson 9.3 (grade 7) · +1 more

gyroscope (rate gyro)English
A sensor of angular velocity (degrees per second); integrating it gives angle, but small errors make the angle drift.
Engineering Design, Robotics & Drones, Lesson 9.3 (grade 9–12)

gyroscopic effectEnglish
When you try to tilt a spinning object, it turns sideways instead.
Grade 4 Engineering & Physics, Lesson 9.2 (grade 4)

gyroscopic stabilityEnglish
The steadiness a spinning object gets from its angular momentum, so it keeps pointing the same way.
Grade 5 Engineering & Physics, Lesson 9.1 (grade 5)

half adderEnglish
A circuit that adds two bits: sum = A \oplus B, carry = AB.
Electronics & Microcontrollers, Lesson 6.3 (grade 9–12)

half-splittingEnglish
Testing at the middle of a signal path to tell which half holds the fault, then halving again, so a fault in n steps is found in about \log_2 n tests.
Electronics & Microcontrollers, Lesson 2.5 (grade 9–12)

hangerEnglish
A thin cable that hangs down from the main cable and holds up the road.
Grade 1 Engineering & Physics, Lesson 2.4 (grade 1)

hardener (curing agent)English
Usually an amine whose hydrogen atoms open the epoxide rings and link resin molecules together.
Shop & Trades, Lesson 2.3 (grade 9–12)

hardwood and softwoodEnglish
Hardwoods come from broad-leaved trees (oak, maple, cherry, walnut) and have vessels or pores; softwoods come from conifers (pine, fir, spruce, cedar). The names describe the tree, not the hardness: balsa is a hardwood.
Shop & Trades, Lesson 3.1 (grade 9–12)

harmonic driveEnglish
A compact gear system with a flexible toothed ring that gives a very large reduction in a small space.
Grade 6 Engineering & Physics, Lesson 8.1 (grade 6)

H-bridgeEnglish
Four switches arranged like the letter H around a motor. Closing one diagonal pair drives current one way; the other pair reverses it.
Electronics & Microcontrollers, Lesson 8.3 (grade 9–12) · Engineering Design, Robotics & Drones, Lesson 6.3 (grade 9–12)

head lossEnglish
The pressure lost to friction as water flows through pipes, valves and fittings. It grows with pipe length and with the square of velocity, and falls sharply with larger diameter.
Grade 8 Engineering & Physics, Lesson 5.2 (grade 8)

header and stretcherEnglish
A header is a brick laid with its end showing, tying two wythes (layers) together; a stretcher shows its long side.
Architecture & Civil Engineering, Lesson 5.2 (grade 9–12)

header, king stud and jack studEnglish
A header is the beam over a door or window opening; it rests on short jack (trimmer) studs, which are nailed to full-height king studs.
Shop & Trades, Lesson 4.2 (grade 9–12)

heat engineEnglish
A machine that turns a flow of heat from a warmer place to a cooler place into motion.
Grade 6 Engineering & Physics, Lesson 9.2 (grade 6) · Grade 7 Engineering & Physics, Lesson 1.2 (grade 7) · Physics, Lesson 8.5 (grade 11–12)

heat exchangerEnglish
The sealed metal passages inside a furnace that keep the combustion gases apart from the house air while passing their heat through the metal.
Shop & Trades, Lesson 6.2 (grade 9–12)

heat inputEnglish
The arc energy delivered per unit length of weld: HI = \dfrac{60VI}{1000S} kJ/in, with S the travel speed in in/min.
Shop & Trades, Lesson 7.2 (grade 9–12)

heat of hydrationEnglish
Heat released as cement reacts with water; in a huge concrete mass it must be removed or the concrete cracks.
Architecture & Civil Engineering, Lesson 8.5 (grade 9–12)

heat pumpEnglish
A refrigeration system that can run in reverse, moving heat from outdoors into the house in winter and from the house to outdoors in summer.
Shop & Trades, Lesson 6.4 (grade 9–12)

heat-affected zone (HAZ)English
The band of base metal next to the weld that did not melt but was heated enough to change its grain structure and properties.
Shop & Trades, Lesson 7.2 (grade 9–12)

heated bedEnglish
The flat build plate, warmed to 50–110 °C so the first layer sticks and the part does not warp as it cools.
Shop & Trades, Lesson 8.2 (grade 9–12)

heating degree days (HDD)English
A measure of how cold a heating season is: the sum over the days of how many degrees the daily mean temperature is below 65 °F.
Shop & Trades, Lesson 4.4 (grade 9–12)

heat-set insertEnglish
A knurled brass sleeve with internal threads, pressed into a printed hole with a hot soldering iron so the plastic melts around it; it gives strong, reusable metal threads.
Shop & Trades, Lesson 8.4 (grade 9–12)

heelEnglish
A sideways tilt of a ship.
Grade 7 Engineering & Physics, Lesson 6.1 (grade 7)

helicopterEnglish
An aircraft that flies with spinning wings on top, so it can go straight up, hover and land almost anywhere.
Grade 2 Engineering & Physics, Lesson 7.4 (grade 2)

helixEnglish
The curve made by wrapping a straight sloped line around a cylinder; the path a screw thread follows.
Shop & Trades, Lesson 1.1 (grade 9–12)

herringboneEnglish
A zigzag pattern of bricks, some laid upright, that locks each new ring of brick in place.
Grade 4 Engineering & Physics, Lesson 3.3 (grade 4)

hexadecimalEnglish
Base 16, using digits 0–9 and A–F (A = 10 … F = 15). One hex digit is exactly four bits.
Electronics & Microcontrollers, Lesson 6.2 (grade 9–12)

hidden lineEnglish
A dashed line showing an edge that cannot be seen in that view.
Engineering Design, Robotics & Drones, Lesson 2.2 (grade 9–12)

hide glueEnglish
Animal glue made by boiling collagen from hides and bones; used hot, it gels as it cools and hardens as it dries; reversible with heat and moisture.
Shop & Trades, Lesson 2.2 (grade 9–12)

high-level languageEnglish
A programming language written in words and symbols people can read, translated into machine instructions by a compiler or interpreter.
Electronics & Microcontrollers, Lesson 9.3 (grade 9–12)

high-performance concreteEnglish
Concrete with special mixes and additives that make it much stronger and easier to pump than ordinary concrete.
Grade 8 Engineering & Physics, Lesson 3.4 (grade 8)

high-strength concreteEnglish
Concrete with compressive strength above about 50–60 MPa, used in the lower columns and walls of supertall towers.
Architecture & Civil Engineering, Lesson 7.4 (grade 9–12)

hoistEnglish
A machine for lifting heavy loads.
Grade 4 Engineering & Physics, Lesson 3.3 (grade 4)

holeEnglish
A missing electron in a semiconductor’s bonds. It moves like a positive charge as neighboring electrons fill it in turn.
Electronics & Microcontrollers, Lesson 4.1 (grade 9–12)

holonomic driveEnglish
A drive (omni, mecanum or swerve) that can move in any direction without turning first.
Engineering Design, Robotics & Drones, Lesson 6.2 (grade 9–12)

Hooke’s lawEnglish
A spring squeezes or stretches in proportion to the force on it: twice the force, twice the squeeze (up to a limit).
Grade 4 Engineering & Physics, Lesson 9.3 (grade 4) · Grade 7 Engineering & Physics, Lesson 3.1 (grade 7) · Grade 8 Engineering & Physics, Lesson 9.2 (grade 8) · +1 more

hoop tensionEnglish
The pull that develops around the lower part of a dome or the base of a cone as it tries to spread outward.
Architecture & Civil Engineering, Lesson 1.3 (grade 9–12) · Grade 4 Engineering & Physics, Lesson 3.3 (grade 4) · Grade 6 Engineering & Physics, Lesson 3.3 (grade 6)

hot endEnglish
The heated block and nozzle that melt the filament; typically 190–260 °C, with a heat break and cooling fan above it so the filament melts only where it should.
Shop & Trades, Lesson 8.2 (grade 9–12)

hot meltEnglish
A thermoplastic adhesive applied molten and set by cooling; it softens again when heated.
Shop & Trades, Lesson 2.4 (grade 9–12)

hot, neutral and groundEnglish
The hot (black or red) carries current at 120 V to the load; the neutral (white) is the grounded return path; the equipment grounding conductor (bare or green) carries current only during a fault.
Shop & Trades, Lesson 5.1 (grade 9–12)

hot work and fire watchEnglish
Hot work is any welding, cutting or grinding that can start a fire. A fire watch is a trained person with an extinguisher who watches during the work and for at least 30 minutes after (OSHA), longer where codes require.
Shop & Trades, Lesson 7.5 (grade 9–12)

hot-air balloonEnglish
A big bag filled with warm air that rises and floats in the sky.
Grade 1 Engineering & Physics, Lesson 7.4 (grade 1) · Grade 5 Engineering & Physics, Lesson 7.1 (grade 5)

hoverEnglish
To stay still in the air.
Grade 2 Engineering & Physics, Lesson 7.4 (grade 2) · Grade 2 Engineering & Physics, Lesson 8.4 (grade 2) · Explore Animals · Ranger, Stop 2.3 (Ages 10–13) · +3 more

Howe trussEnglish
A truss with diagonals in compression (timber) and verticals in tension (iron rods) (William Howe, 1840).
Architecture & Civil Engineering, Lesson 6.5 (grade 9–12)

HTTPEnglish
The protocol by which web browsers request pages and servers send them.
Electronics & Microcontrollers, Lesson 10.3 (grade 9–12)

hull speedEnglish
The speed at which the ship’s own bow wave is as long as its waterline, so the hull sits in its own wave trough: about 1.34 × √(waterline length in feet) knots.
Grade 8 Engineering & Physics, Lesson 6.1 (grade 8)

human in the loopEnglish
A design in which a person supervises, approves or can override an automatic system.
Engineering Design, Robotics & Drones, Lesson 8.5 (grade 9–12)

HVACEnglish
Heating, ventilation and air conditioning: the systems that keep a building’s air comfortable and fresh.
Grade 6 Engineering & Physics, Lesson 3.4 (grade 6)

hybrid jointEnglish
A joint that uses both adhesive and mechanical fasteners, such as glue-and-screw, rivet-bonded or weld-bonded joints.
Shop & Trades, Lesson 2.5 (grade 9–12)

hydraulic cementEnglish
Cement that hardens even under water.
Grade 4 Engineering & Physics, Lesson 6.4 (grade 4)

hydraulicsEnglish
Using a liquid in pipes or tubes to pass along a push and move things.
Grade 4 Engineering & Physics, Lesson 8.4 (grade 4)

hydronic heatingEnglish
Heating with hot water from a boiler pumped through radiators, baseboards or tubing in floors.
Shop & Trades, Lesson 6.2 (grade 9–12)

hydrostatic pressureEnglish
Water pressure, which increases linearly with depth: p = \gamma_w h.
Architecture & Civil Engineering, Lesson 8.5 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 5.2 (grade 8)

hygroscopicEnglish
Absorbing water from the air. Brake fluid is hygroscopic, so it must be replaced on a schedule.
Shop & Trades, Lesson 10.2 (grade 9–12) · Grade 8 Gardening & Animals, Lesson 6.4 (grade 8)

hyperbolic cosineEnglish
\cosh x = \tfrac{1}{2}(e^x + e^{-x}); it describes the catenary.
Architecture & Civil Engineering, Lesson 4.4 (grade 9–12)

I²CEnglish
Inter-Integrated Circuit: two shared wires, SDA (data) and SCL (clock), with pull-up resistors. Each device has a 7-bit address, so many devices share the same two wires.
Electronics & Microcontrollers, Lesson 10.1 (grade 9–12)

IDEEnglish
Integrated development environment: the program (the microcontroller IDE) in which you write, verify (compile) and upload code.
Electronics & Microcontrollers, Lesson 7.1 (grade 9–12)

ideal mechanical advantage (IMA)English
The mechanical advantage with no friction, found from distances: input distance divided by output distance.
Engineering Design, Robotics & Drones, Lesson 4.1 (grade 9–12)

idler gearEnglish
A gear placed between two others that changes the direction of rotation but not the overall ratio.
Engineering Design, Robotics & Drones, Lesson 4.2 (grade 9–12)

iglooEnglish
A dome-shaped house built from blocks of hard snow.
Grade 2 Engineering & Physics, Lesson 3.2 (grade 2) · Grade 1 Geography: Maps and Journeys, Lesson 5.2 (grade 1)

impact parameterEnglish
How far off-center one ball strikes another; it sets the angles at which they leave.
Physics, Lesson 6.5 (grade 11–12)

impulseEnglish
Force × time. A solenoid gives the ball a large force for a very short time.
Grade 7 Engineering & Physics, Lesson 9.1 (grade 7) · Grade 8 Engineering & Physics, Lesson 1.2 (grade 8) · Physics, Lesson 6.1 (grade 11–12) · +3 more

impulse–momentum theoremEnglish
The impulse on an object equals its change in momentum: \vec{F}_{\text{avg}}\Delta t = \Delta\vec{p}.
Physics, Lesson 6.1 (grade 11–12)

IMUEnglish
Inertial measurement unit: a chip with gyroscopes (rotation rate) and accelerometers (acceleration, including gravity), often with a magnetometer.
Engineering Design, Robotics & Drones, Lesson 9.3 (grade 9–12) · Grade 6 Engineering & Physics, Lesson 8.4 (grade 6)

inclined planeEnglish
A flat, slanted surface, like a ramp, that makes it easier to raise a load.
Grade 3 Engineering & Physics, Lesson 1.4 (grade 3) · Grade 6 Engineering & Physics, Lesson 1.3 (grade 6) · Physics, Lesson 2.1 (grade 11–12)

inclining testEnglish
A test in which known weights are moved across a ship’s deck and the tilt is measured to find out how stable the ship is.
Grade 5 Engineering & Physics, Lesson 6.2 (grade 5)

indentationEnglish
In Python, the spaces at the start of a line show which lines belong inside an if, loop or function. Four spaces per level is the standard.
Electronics & Microcontrollers, Lesson 9.3 (grade 9–12)

independence of motionEnglish
The horizontal motion (constant velocity) and the vertical motion (constant acceleration g downward) of a projectile happen at the same time without affecting each other.
Physics, Lesson 2.5 (grade 11–12)

independent testEnglish
A check done with a different method or by different people, so that one mistake cannot fool every test.
Engineering Design, Robotics & Drones, Lesson 10.3 (grade 9–12)

index of refractionEnglish
n = c/v, how many times slower light travels in a material than in a vacuum: water 1.33, glass about 1.5, diamond 2.42.
Physics, Lesson 9.4 (grade 11–12)

index of refraction (n)English
How much a material slows light: n = c ÷ v. Air ≈ 1.00, water ≈ 1.33, glass fiber core ≈ 1.47.
Grade 8 Engineering & Physics, Lesson 5.3 (grade 8)

induced velocityEnglish
The extra downward speed given to the air passing through a rotor.
Engineering Design, Robotics & Drones, Lesson 9.2 (grade 9–12)

inductance (L)English
How strongly a coil opposes a change in current: V = L\,\Delta I/\Delta t. Unit: the henry (H).
Electronics & Microcontrollers, Lesson 3.3 (grade 9–12)

inductionEnglish
Charging or polarizing an object by bringing a charge near it, without touching, so its own charges shift.
Physics, Lesson 10.1 (grade 11–12)

inductorEnglish
A coil of wire, often around an iron core, that stores energy in its magnetic field and opposes changes in current.
Electronics & Microcontrollers, Lesson 3.3 (grade 9–12)

inelastic collisionEnglish
A collision in which some kinetic energy becomes heat, sound or permanent deformation; momentum is still conserved.
Physics, Lesson 6.3 (grade 11–12)

inertial balanceEnglish
A device that measures mass by how fast an object oscillates on a spring, without using its weight.
Physics, Lesson 3.2 (grade 11–12)

inertial measurement unit (IMU)English
A chip with gyroscopes and accelerometers that senses rotation and tilt, used by the flight controller.
Grade 7 Engineering & Physics, Lesson 8.4 (grade 7) · Grade 8 Engineering & Physics, Lesson 7.4 (grade 8)

inertial reference frameEnglish
A point of view (such as the ground, for most purposes) from which Newton’s first law holds: objects with no net force move at constant velocity.
Physics, Lesson 3.2 (grade 11–12)

infillEnglish
The internal pattern (grid, gyroid, honeycomb) that fills the inside of a part at a set percentage, usually 10–40%.
Shop & Trades, Lesson 8.3 (grade 9–12)

infrared remoteEnglish
A remote control that sends codes as bursts of invisible infrared light, switched on and off at about 38 kHz.
Electronics & Microcontrollers, Lesson 10.2 (grade 9–12)

injection moldingEnglish
A process in which melted plastic is forced under high pressure into a steel mold, cooled until solid, and ejected; each cycle takes seconds.
Engineering Design, Robotics & Drones, Lesson 3.5 (grade 9–12) · Grade 5 Engineering & Physics, Lesson 9.2 (grade 5) · Grade 7 Engineering & Physics, Lesson 9.4 (grade 7)

INPUT_PULLUPEnglish
A pin mode that turns on a resistor of about 20–50 kΩ inside the chip from the pin to 5 V. The button then connects the pin to ground, so pressed reads LOW.
Electronics & Microcontrollers, Lesson 7.3 (grade 9–12)

instantaneous velocityEnglish
The velocity at a single instant: the slope of the tangent line to the position–time curve at that time.
Physics, Lesson 2.4 (grade 11–12)

instrument flyingEnglish
Flying by reference to instruments instead of looking outside, as in clouds or darkness.
Engineering Design, Robotics & Drones, Lesson 9.5 (grade 9–12) · Explore Travel and Faraway Places · Ranger, Stop 3.8 (Ages 10–13)

insulated wireEnglish
Wire with a thin coating that keeps the electricity inside the wire.
Grade 2 Engineering & Physics, Lesson 4.4 (grade 2) · Grade 4 Engineering & Physics, Lesson 4.2 (grade 4)

integral gain (Ki)English
How strongly it responds to error that has built up over time; it removes steady-state error but can cause overshoot.
Engineering Design, Robotics & Drones, Lesson 7.4 (grade 9–12)

integrated circuit (IC)English
A complete circuit of many transistors, resistors and connections made together on one small chip of semiconductor.
Grade 8 Engineering & Physics, Lesson 4.2 (grade 8)

integrated circuit (IC, chip)English
A complete circuit of transistors, resistors and connections made together on one piece of semiconductor.
Electronics & Microcontrollers, Lesson 4.5 (grade 9–12)

intellectual property (IP)English
Creations of the mind, such as inventions, designs, writings, names and secret methods, that the law can protect.
Engineering Design, Robotics & Drones, Lesson 10.2 (grade 9–12)

intercepting sewerEnglish
A large sewer running across the ends of smaller sewers to catch their flow and carry it away.
Architecture & Civil Engineering, Lesson 9.3 (grade 9–12) · Grade 4 Engineering & Physics, Lesson 5.4 (grade 4) · Grade 5 Engineering & Physics, Lesson 5.2 (grade 5)

interchangeabilityEnglish
Making parts so accurately to a standard that any nut fits any bolt of the same size, wherever it was made.
Shop & Trades, Lesson 1.1 (grade 9–12)

interferenceEnglish
Two parts occupying the same space in a model, which would be impossible in reality; CAD can detect it automatically.
Engineering Design, Robotics & Drones, Lesson 2.5 (grade 9–12) · Physics, Lesson 9.5 (grade 11–12)

interlockEnglish
A safety device that prevents a dangerous action unless conditions are safe, such as a door switch that stops a machine.
Engineering Design, Robotics & Drones, Lesson 8.5 (grade 9–12) · Grade 2 Engineering & Physics, Lesson 9.2 (grade 2) · Textile Science & Clothing Construction, Lesson 5.4 (grade 9–12)

interlockingEnglish
Held together because the shapes of the pieces hook into one another, without glue or fasteners.
Grade 5 Engineering & Physics, Lesson 9.3 (grade 5)

internal resistanceEnglish
Resistance inside a battery that makes its voltage drop under load and turns some energy into heat.
Engineering Design, Robotics & Drones, Lesson 6.4 (grade 9–12)

internal-combustion engineEnglish
An engine that burns its fuel inside the cylinder, so the hot gases push directly on the piston.
Grade 7 Engineering & Physics, Lesson 1.3 (grade 7)

interpreterEnglish
A program that reads and runs code line by line. Python is usually interpreted, so you can type a line and see its result at once.
Electronics & Microcontrollers, Lesson 9.3 (grade 9–12)

interrupt (IRQ)English
A signal that makes the processor stop what it is doing and run a short handler function at once, such as when a button is pressed.
Electronics & Microcontrollers, Lesson 9.5 (grade 9–12)

IP addressEnglish
A number that identifies a device on a network, such as 192.168.1.42 on a home network.
Electronics & Microcontrollers, Lesson 10.3 (grade 9–12)

IR reflectance sensorEnglish
A sensor with an infrared emitter and detector that reads how much light a surface reflects; dark lines reflect little.
Engineering Design, Robotics & Drones, Lesson 7.5 (grade 9–12)

iron coreEnglish
The iron bar or nail inside the coil that makes the magnet much stronger.
Grade 2 Engineering & Physics, Lesson 4.4 (grade 2)

irrigationEnglish
Bringing water to fields so crops can grow.
Grade 3 Engineering & Physics, Lesson 1.4 (grade 3) · Grade 7 Geography: Regions of the World, Lesson 3.1 (grade 7) · Grade 7 Geography: Regions of the World, Lesson 5.2 (grade 7)

isochronismEnglish
The property of taking the same time for every swing, whatever its size; a pendulum has it only for small swings.
Physics, Lesson 9.1 (grade 11–12)

isolated systemEnglish
A system with no net external force, so its total momentum is conserved.
Physics, Lesson 6.2 (grade 11–12)

isometric drawingEnglish
A pictorial drawing in which the three axes are drawn 120° apart and lengths along them are drawn at the same scale.
Architecture & Civil Engineering, Lesson 2.5 (grade 9–12) · Engineering Design, Robotics & Drones, Lesson 2.1 (grade 9–12)

isometric projectionEnglish
The true geometric view of an object seen along a cube’s diagonal, in which edges along the axes appear foreshortened to about 82% of their length.
Engineering Design, Robotics & Drones, Lesson 2.1 (grade 9–12)

jack standEnglish
A fixed, locking stand that holds a raised car safely; a jack is only for lifting.
Shop & Trades, Lesson 10.5 (grade 9–12)

jacking pointEnglish
The reinforced spot on the car’s body or frame, shown in the manual, where a jack may lift it safely.
Shop & Trades, Lesson 10.5 (grade 9–12)

jackscrewEnglish
A big screw that lifts a heavy load a little at each turn.
Grade 3 Engineering & Physics, Lesson 5.2 (grade 3)

jetEnglish
A precisely sized hole that meters fuel into the airstream; main jets feed at speed, idle jets at low throttle.
Shop & Trades, Lesson 9.3 (grade 9–12)

jet engineEnglish
An engine that sucks in air, squeezes it, burns fuel in it and blasts the hot gas out the back to make thrust.
Grade 5 Engineering & Physics, Lesson 7.4 (grade 5) · Technology Overcoming Geography, Lesson 4.4 (grade 9–12)

jig and fixtureEnglish
Devices that guide a tool (jig) or hold a workpiece (fixture) in exactly the same position every time, so every part comes out alike.
Engineering Design, Robotics & Drones, Lesson 3.3 (grade 9–12)

joint (node)English
A point where members meet. In truss analysis, joints are treated as pins that cannot carry bending.
Grade 8 Engineering & Physics, Lesson 2.3 (grade 8)

joint stiffnessEnglish
How much the clamped parts resist being squeezed; a stiff joint keeps most of an outside load out of the bolt.
Shop & Trades, Lesson 1.3 (grade 9–12)

joistEnglish
One of the parallel horizontal members that carry a floor or ceiling, set on edge and spanning between walls or beams.
Shop & Trades, Lesson 4.2 (grade 9–12)

Joule heatingEnglish
The heat produced when current flows through resistance, at a rate P = I^2 R.
Electronics & Microcontrollers, Lesson 1.4 (grade 9–12)

junction dotEnglish
A dot where crossing lines are joined. Lines that cross without a dot are not connected.
Electronics & Microcontrollers, Lesson 2.4 (grade 9–12)

kaleidoscopeEnglish
A tube with mirrors inside that turns a few colored bits into a beautiful repeating pattern.
Grade 1 Engineering & Physics, Lesson 9.3 (grade 1)

keelEnglish
The strong backbone that runs along the bottom of a boat from front to back.
Grade 2 Engineering & Physics, Lesson 6.3 (grade 2) · Grade 3 Engineering & Physics, Lesson 6.2 (grade 3) · Explore Animals · Expert, Stop 2.5 (Ages 14+) · +1 more

kerfEnglish
The width of material removed by a cutting tool or laser beam.
Engineering Design, Robotics & Drones, Lesson 3.4 (grade 9–12) · Shop & Trades, Lesson 3.2 (grade 9–12)

kern (middle third)English
The central zone of a foundation within which the resultant load must stay for the whole base to remain in compression.
Architecture & Civil Engineering, Lesson 8.3 (grade 9–12)

kernel (filter)English
A small grid of numbers slid across an image and multiplied with the pixels under it, to blur, sharpen or find edges.
Engineering Design, Robotics & Drones, Lesson 8.3 (grade 9–12)

keyEnglish
The switch on a telegraph that the operator taps to send dots and dashes.
Grade 2 Engineering & Physics, Lesson 4.3 (grade 2) · Grade 3 Engineering & Physics, Lesson 4.4 (grade 3) · Grade 5 Engineering & Physics, Lesson 4.3 (grade 5) · +1 more

keystoneEnglish
The wedge-shaped stone at the very top of an arch that locks the other stones in place.
Grade 1 Engineering & Physics, Lesson 2.3 (grade 1) · Grade 2 Engineering & Physics, Lesson 2.3 (grade 2) · Grade 3 Engineering & Physics, Lesson 2.3 (grade 3) · +3 more

kickbackEnglish
A sudden violent throw of the workpiece back toward the operator, caused when the rising teeth at the back of a spinning blade catch the wood.
Shop & Trades, Lesson 3.3 (grade 9–12)

kilopascal (kPa)English
1,000 pascals; a unit of pressure. 1 psi is about 6.9 kPa.
Grade 6 Engineering & Physics, Lesson 5.2 (grade 6)

kilowatt-hourEnglish
A unit of energy used for electricity: the energy delivered by 1 kW for 1 hour, 3.6 \times 10^6\ \text{J}.
Physics, Lesson 5.4 (grade 11–12) · Shop & Trades, Lesson 5.1 (grade 9–12)

kindergartenEnglish
A German word that means “children’s garden.” It is the first year of school.
Kindergarten Engineering & Physics, Lesson 9.4 (grade K)

kinetic energyEnglish
The energy of something that is moving. The faster it moves, the more kinetic energy it has.
Grade 4 Engineering & Physics, Lesson 1.1 (grade 4) · Grade 6 Engineering & Physics, Lesson 9.1 (grade 6) · Grade 7 Engineering & Physics, Lesson 1.4 (grade 7) · +3 more

kinetic frictionEnglish
The force that opposes sliding once it has started: f_k = \mu_k N, nearly independent of speed.
Physics, Lesson 3.4 (grade 11–12)

Kirchhoff’s current law (KCL)English
The total current flowing into a node equals the total current flowing out. Charge is not created or destroyed.
Electronics & Microcontrollers, Lesson 2.2 (grade 9–12)

Kirchhoff’s voltage law (KVL)English
Around any closed loop, the sum of the voltage rises equals the sum of the voltage drops. Energy is conserved.
Electronics & Microcontrollers, Lesson 2.2 (grade 9–12)

kitEnglish
A packaged set of parts, a board and instructions from which a builder assembles a working device.
Electronics & Microcontrollers, Lesson 5.5 (grade 9–12)

kiteEnglish
A light frame covered with paper or cloth that the wind holds up while a string holds it down.
Grade 2 Engineering & Physics, Lesson 7.2 (grade 2) · Kindergarten Engineering & Physics, Lesson 7.3 (grade K) · Sports & Games of the World, Lesson 4.3 (grade 4–7) · +3 more

knife lineEnglish
A line cut into the wood with a marking knife; it is finer than a pencil line and gives the saw or chisel a crisp starting shoulder.
Shop & Trades, Lesson 3.2 (grade 9–12)

knotEnglish
One nautical mile per hour, about 1.15 mph or 0.514 m/s.
Grade 8 Engineering & Physics, Lesson 6.1 (grade 8) · Explore Crafts and Making, Stop 1.2 (Ages 7–9) · Tactics & Strategy, Lesson 4.3 (grade 8–12) · +3 more

known goodEnglish
A part, circuit or value that is known to work, used for comparison.
Electronics & Microcontrollers, Lesson 2.5 (grade 9–12)

Kremer PrizeEnglish
A prize offered in 1959 by industrialist Henry Kremer for the first human-powered aircraft to fly a figure-eight course around two markers half a mile apart.
Grade 8 Engineering & Physics, Lesson 7.1 (grade 8)

L293DEnglish
A chip with two H-bridges (up to about 600 mA each) and built-in protection diodes, with separate supplies for logic (5 V) and motors.
Electronics & Microcontrollers, Lesson 8.3 (grade 9–12)

lacingEnglish
The small diagonal bars that tie together the separate plates of a built-up compression member so they act as one.
Architecture & Civil Engineering, Lesson 6.4 (grade 9–12) · Grade 7 Engineering & Physics, Lesson 2.4 (grade 7) · Threads & Weaving, Lesson 3.1 (grade 9–12)

landfallEnglish
The first sight of land after crossing the sea.
Grade 6 Engineering & Physics, Lesson 7.3 (grade 6) · Grade 7 Spanish, Lesson 1.1 (grade 7)

lanternEnglish
A small tower with openings on top of a dome, letting light in and crowning the building.
Architecture & Civil Engineering, Lesson 1.3 (grade 9–12) · Grade 6 Engineering & Physics, Lesson 3.3 (grade 6) · Explore Animals · Expert, Stop 5.6 (Ages 14+) · +1 more

latchEnglish
A circuit with two stable states that remembers one bit. An SR latch has Set and Reset inputs.
Electronics & Microcontrollers, Lesson 6.4 (grade 9–12) · Grade 1 Engineering & Physics, Lesson 9.4 (grade 1)

lateral loadEnglish
A sideways load, from wind or earthquakes, that tries to bend and overturn a building.
Architecture & Civil Engineering, Lesson 7.3 (grade 9–12) · Grade 5 Engineering & Physics, Lesson 3.1 (grade 5)

latticeEnglish
A pattern of crossing pieces with open spaces between them.
Grade 1 Engineering & Physics, Lesson 3.4 (grade 1) · Grade 2 Engineering & Physics, Lesson 2.2 (grade 2) · Grade 3 Engineering & Physics, Lesson 3.3 (grade 3)

launch angleEnglish
The tilt of a launcher, measured from the ground.
Grade 3 Engineering & Physics, Lesson 7.1 (grade 3) · Physics, Lesson 2.5 (grade 11–12)

law and theoryEnglish
A scientific law describes a pattern (Kepler’s laws say how planets move); a theory explains why (Newton’s gravitation explains Kepler’s laws).
Physics, Lesson 1.1 (grade 11–12)

law of reflectionEnglish
The angle of reflection equals the angle of incidence, both measured from the normal (the line perpendicular to the surface).
Physics, Lesson 9.4 (grade 11–12) · Body Mechanics of Sport, Lesson 4.4 (grade 8–12)

law of the leverEnglish
A lever balances when the torques on the two sides are equal: F_1d_1 = F_2d_2.
Physics, Lesson 7.1 (grade 11–12)

law of universal gravitationEnglish
Every two masses attract each other with a force F = Gm_1m_2/r^2, along the line between their centers.
Physics, Lesson 4.2 (grade 11–12)

layer heightEnglish
The thickness of each printed layer, typically 0.1–0.3 mm for FDM and 0.025–0.1 mm for resin.
Shop & Trades, Lesson 8.1 (grade 9–12)

layoutEnglish
The physical arrangement of parts and connections on a board, planned from the schematic.
Electronics & Microcontrollers, Lesson 5.1 (grade 9–12)

LCD (liquid-crystal display)English
A display in which liquid crystals between polarizing filters twist light so that each segment or pixel appears dark or clear when a voltage is applied.
Electronics & Microcontrollers, Lesson 8.4 (grade 9–12)

lead (L)English
How far the screw advances in one full turn. For an ordinary single-start thread the lead equals the pitch.
Shop & Trades, Lesson 1.1 (grade 9–12)

lead screwEnglish
A precise long screw on a lathe that drives the cutting tool along the work at an exact rate, so the lathe can cut a thread of exact pitch.
Shop & Trades, Lesson 1.1 (grade 9–12)

lead–acid batteryEnglish
The standard car battery: six cells of lead and lead dioxide plates in sulfuric acid, each about 2.1 V, for about 12.6 V when fully charged.
Shop & Trades, Lesson 10.4 (grade 9–12)

leanEnglish
To tip to one side.
Grade 2 Engineering & Physics, Lesson 3.1 (grade 2) · Grade 1 Gardening & Animals, Lesson 5.3 (grade 1)

leaning instabilityEnglish
A condition in which a tall structure on soft ground leans more because its own lean shifts load to the soft side, which settles more, which increases the lean.
Architecture & Civil Engineering, Lesson 8.3 (grade 9–12)

LEDEnglish
Light-emitting diode: a tiny light that needs very little current and works only one way around.
Grade 4 Engineering & Physics, Lesson 4.1 (grade 4) · Grade 5 Engineering & Physics, Lesson 4.4 (grade 5)

LED driverEnglish
The electronics inside an LED bulb that turn 120 V AC into the low, steady DC current the LEDs need.
Shop & Trades, Lesson 5.5 (grade 9–12)

LED (light-emitting diode)English
A diode that gives off light when current flows forward through it, as electrons drop across the junction and release photons.
Electronics & Microcontrollers, Lesson 3.5 (grade 9–12) · Grade 7 Engineering & Physics, Lesson 4.1 (grade 7)

Lenz’s lawEnglish
An induced current flows in the direction that opposes the change that caused it (the minus sign in Faraday’s law).
Physics, Lesson 10.4 (grade 11–12)

let-go currentEnglish
The current at which muscles clamp onto a conductor so that a person cannot release it; roughly 6 to 16 mA at 60 Hz for adults.
Shop & Trades, Lesson 5.3 (grade 9–12)

leverEnglish
A stiff bar that turns on one point to help lift or move a load.
Grade 1 Engineering & Physics, Lesson 1.1 (grade 1) · Grade 2 Engineering & Physics, Lesson 1.4 (grade 2) · Grade 2 Engineering & Physics, Lesson 9.3 (grade 2) · +3 more

lever armEnglish
The perpendicular distance from the axis to the line along which a force acts; torque = force × lever arm.
Physics, Lesson 7.1 (grade 11–12)

lidarEnglish
Light detection and ranging: a sensor that times laser pulses to measure distances in many directions, building a 3D point cloud.
Engineering Design, Robotics & Drones, Lesson 8.4 (grade 9–12) · Grade 7 Engineering & Physics, Lesson 8.3 (grade 7)

life-cycle costEnglish
The total cost of a building over its life: construction plus energy, maintenance and repairs.
Architecture & Civil Engineering, Lesson 10.4 (grade 9–12)

liftEnglish
The upward push of the air on a moving wing.
Grade 1 Engineering & Physics, Lesson 7.3 (grade 1) · Grade 2 Engineering & Physics, Lesson 7.1 (grade 2) · Grade 3 Engineering & Physics, Lesson 7.2 (grade 3) · +3 more

lift coefficient (CL)English
A number that describes how much lift a wing shape makes at a given angle of attack, measured in wind tunnels.
Grade 7 Engineering & Physics, Lesson 7.1 (grade 7)

lift equationEnglish
L = ½ρv²SCL, where ρ is air density, v is airspeed, S is wing area and CL is the lift coefficient (set by wing shape and angle of attack).
Grade 8 Engineering & Physics, Lesson 7.1 (grade 8)

lift hillEnglish
The first climb of a roller coaster, where a chain or cable gives the train the gravitational potential energy for the whole ride.
Physics, Lesson 5.5 (grade 11–12)

light sensorEnglish
A sensor that notices how bright it is.
Grade 2 Engineering & Physics, Lesson 8.3 (grade 2)

lighthouseEnglish
A tower with a bright light that warns ships of rocks and guides them to safe harbor.
Grade 3 Engineering & Physics, Lesson 6.4 (grade 3) · Kindergarten Engineering & Physics, Lesson 3.4 (grade K) · Grade 2 Geography: Our Country, Coast to Coast, Lesson 2.1 (grade 2)

light-time delayEnglish
The time a radio signal takes to travel between Earth and Mars, from about 3 to 22 minutes one way, depending on the planets’ positions.
Engineering Design, Robotics & Drones, Lesson 8.2 (grade 9–12)

limitsEnglish
The largest and smallest acceptable sizes of a feature.
Engineering Design, Robotics & Drones, Lesson 2.3 (grade 9–12)

line of thrustEnglish
The path of the compressive force through an arch. If it stays within the masonry (ideally the middle third), the arch stands.
Architecture & Civil Engineering, Lesson 4.4 (grade 9–12)

line spectrumEnglish
The set of sharp wavelengths emitted by a gas of one element, its “fingerprint”; for hydrogen, explained by electrons jumping between energy levels.
Physics, Lesson 10.5 (grade 11–12)

linear regulatorEnglish
A regulator (such as the 7805) that drops excess voltage as heat to give a steady output: simple and quiet, but wasteful when the input is much higher than the output.
Electronics & Microcontrollers, Lesson 5.4 (grade 9–12)

linearizeEnglish
To graph transformed variables (such as d against t^2) so that a curved relationship becomes a straight line whose slope can be measured.
Physics, Lesson 2.1 (grade 11–12)

linemanEnglish
A worker who builds and fixes power lines.
Grade 1 Engineering & Physics, Lesson 5.2 (grade 1)

lineworkerEnglish
A trained worker who builds and repairs power lines.
Grade 3 Engineering & Physics, Lesson 5.3 (grade 3) · Grade 5 Engineering & Physics, Lesson 5.4 (grade 5) · Grade 8 Engineering & Physics, Lesson 5.4 (grade 8) · +1 more

linkageEnglish
A mechanism made of rigid bars (links) connected by joints, used to turn one motion into another.
Engineering Design, Robotics & Drones, Lesson 4.3 (grade 9–12) · Grade 3 Engineering & Physics, Lesson 8.3 (grade 3)

liquid-fueled rocketEnglish
A rocket that pumps or pushes a liquid fuel and a liquid oxidizer (such as liquid oxygen) into a chamber where they burn.
Grade 6 Engineering & Physics, Lesson 7.4 (grade 6)

live demoEnglish
Showing the product working, live or on video.
Engineering Design, Robotics & Drones, Lesson 10.5 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 8.4 (grade 8)

live loadEnglish
Weight that comes and goes: people, furniture, books, cars, rain and snow.
Grade 5 Engineering & Physics, Lesson 3.1 (grade 5)

live load (L)English
The weight of people, furniture and movable contents, set by building codes by use: about 40 psf for homes, 50 psf for offices, 100 psf for corridors and assembly areas with movable seats.
Architecture & Civil Engineering, Lesson 4.1 (grade 9–12)

live–dead–liveEnglish
The verification method: test your tester on a known live source, test the circuit you will work on, then test the tester again on the known live source, to be sure a dead reading was not a dead tester.
Shop & Trades, Lesson 5.4 (grade 9–12)

loadEnglish
The thing you want to lift or move.
Grade 1 Engineering & Physics, Lesson 1.1 (grade 1) · Grade 2 Engineering & Physics, Lesson 1.4 (grade 2) · Grade 2 Engineering & Physics, Lesson 6.2 (grade 2) · +3 more

load and effortEnglish
The load is the weight being moved. The effort is the force you use to move it.
Grade 5 Engineering & Physics, Lesson 1.3 (grade 5)

load combinationEnglish
A code rule that adds the loads with factors for safety, such as 1.2D + 1.6L.
Architecture & Civil Engineering, Lesson 4.1 (grade 9–12)

load factorEnglish
A number greater than 1 that a design code multiplies loads by, so the structure is designed for loads larger than expected.
Grade 8 Engineering & Physics, Lesson 2.1 (grade 8)

load lineEnglish
A mark on a ship’s side showing how low it may safely sit in the water when loaded; also called the Plimsoll line.
Grade 4 Engineering & Physics, Lesson 6.2 (grade 4) · Grade 6 Engineering & Physics, Lesson 6.2 (grade 6)

load pathEnglish
The route a load travels through a structure, from where it is applied down to the ground.
Architecture & Civil Engineering, Lesson 4.5 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 2.1 (grade 8) · Shop & Trades, Lesson 4.2 (grade 9–12)

load sheddingEnglish
Deliberately cutting power to some customers to keep the rest of the grid from collapsing.
Grade 8 Engineering & Physics, Lesson 5.1 (grade 8)

load testEnglish
A test where weight is added to a structure to see how much it can hold.
Grade 4 Engineering & Physics, Lesson 2.2 (grade 4)

load-bearing wallEnglish
A wall that holds up the weight of the floors and roof above it.
Grade 3 Engineering & Physics, Lesson 3.4 (grade 3) · Grade 5 Engineering & Physics, Lesson 3.3 (grade 5)

loadingEnglish
The change a meter causes in the circuit it measures, because the meter itself draws some current or adds some resistance.
Electronics & Microcontrollers, Lesson 1.5 (grade 9–12) · Electronics & Microcontrollers, Lesson 2.3 (grade 9–12)

lockout and labelingEnglish
Holding the breaker off with a breaker lock (or at least tape) and a label saying who is working on it, so that no one can switch it on while you work.
Shop & Trades, Lesson 5.4 (grade 9–12)

locomotiveEnglish
An engine on wheels that pulls a train; in 1829, a steam engine on rails.
Grade 6 Engineering & Physics, Lesson 1.1 (grade 6) · Grade 2 Geography: Our Country, Coast to Coast, Lesson 8.2 (grade 2) · Grade 4 Geography: The United States: Regions, Rivers and Routes, Lesson 7.1 (grade 4) · +1 more

lodestoneEnglish
A natural rock that is magnetic.
Grade 3 Engineering & Physics, Lesson 4.3 (grade 3) · Explore Travel and Faraway Places · Expert, Stop 1.2 (Ages 14+) · Grade 1 Geography: Maps and Journeys, Lesson 2.3 (grade 1) · +1 more

logic gateEnglish
A circuit that produces a digital output from one or more digital inputs by a fixed rule.
Electronics & Microcontrollers, Lesson 6.3 (grade 9–12) · Grade 8 Engineering & Physics, Lesson 4.1 (grade 8)

logisticsEnglish
The planning of how materials, tools, workers and food arrive where and when they are needed.
Architecture & Civil Engineering, Lesson 1.2 (grade 9–12) · Tactics & Strategy, Lesson 6.2 (grade 8–12) · Geography and History: Why Borders Fall Where They Do, Lesson 7.4 (grade 9–12)

long grain and end grainEnglish
Long grain is the side of a board, where fibers lie along the surface; end grain is the cut end, where fibers are cut across like a bundle of straws.
Shop & Trades, Lesson 2.2 (grade 9–12) · Shop & Trades, Lesson 3.4 (grade 9–12)

longitudinal and transverse wavesEnglish
In a longitudinal wave, coils move back and forth along the direction the wave travels (like sound); in a transverse wave they move sideways.
Grade 8 Engineering & Physics, Lesson 9.2 (grade 8)

look-aheadEnglish
How far in front of the wheels the sensors see; more look-ahead allows higher speed.
Engineering Design, Robotics & Drones, Lesson 7.5 (grade 9–12)

loopEnglish
Any closed path through a circuit that returns to its starting point.
Electronics & Microcontrollers, Lesson 2.2 (grade 9–12) · Engineering Design, Robotics & Drones, Lesson 7.2 (grade 9–12) · Grade 3 Engineering & Physics, Lesson 8.2 (grade 3) · +3 more

loop and conditionalEnglish
A loop repeats instructions (while, for); a conditional chooses what to do based on a test (if, else).
Grade 8 Engineering & Physics, Lesson 4.3 (grade 8)

loop-the-loopEnglish
A vertical loop on a track. To stay on the track at the top, an object needs a speed of at least \sqrt{gr}.
Physics, Lesson 5.5 (grade 11–12)

low-side switchEnglish
A switch placed between the load and ground. An NPN transistor is usually used this way, with its emitter to ground.
Electronics & Microcontrollers, Lesson 4.2 (grade 9–12)

lug nutsEnglish
The nuts that hold a wheel to the hub studs; tightened to a set torque in a star pattern.
Shop & Trades, Lesson 10.5 (grade 9–12)

lumenEnglish
The unit of visible light output. A traditional 60 W incandescent bulb gives about 800 lumens.
Shop & Trades, Lesson 5.5 (grade 9–12)

macadamEnglish
John McAdam’s road of small, angular broken stones compacted in layers on a well-drained, crowned subgrade (1810s–1820s).
Architecture & Civil Engineering, Lesson 9.4 (grade 9–12) · Grade 2 Engineering & Physics, Lesson 5.4 (grade 2)

Mach numberEnglish
Speed ÷ speed of sound. Mach 1 is the speed of sound; Mach 2 is twice it.
Grade 7 Engineering & Physics, Lesson 7.4 (grade 7) · Physics, Lesson 9.3 (grade 11–12)

machine learningEnglish
Methods in which a computer learns patterns, such as what a stop sign looks like, from many labeled examples rather than hand-written rules.
Engineering Design, Robotics & Drones, Lesson 8.3 (grade 9–12) · Tactics & Strategy, Lesson 2.1 (grade 4–7)

machine.PinEnglish
The MicroPython class that controls a GPIO pin: led = Pin(15, Pin.OUT), then led.value(1) or led.toggle().
Electronics & Microcontrollers, Lesson 9.4 (grade 9–12)

magneticEnglish
Pulled by a magnet. Iron and steel things are magnetic.
Kindergarten Engineering & Physics, Lesson 4.2 (grade K)

magnetic fluxEnglish
The amount of magnetic field passing through an area, \Phi = BA\cos\theta, measured in webers (Wb = T·m²).
Physics, Lesson 10.4 (grade 11–12)

magnetic force on a currentEnglish
F = BIL\sin\theta on a wire of length L; on a moving charge, F = qvB\sin\theta, perpendicular to both the velocity and the field.
Physics, Lesson 10.3 (grade 11–12)

magnetic polesEnglish
The two ends of a magnet, north and south; like poles repel, unlike poles attract, and poles always come in pairs.
Physics, Lesson 10.3 (grade 11–12)

magnetic tractionEnglish
Magnets under a slot car that pull it toward the steel rails, pressing it down harder so it can corner faster.
Grade 7 Engineering & Physics, Lesson 9.2 (grade 7)

magnetoEnglish
A generator that makes the ignition spark from magnets passing a coil, needing no battery.
Shop & Trades, Lesson 9.4 (grade 9–12)

main breakerEnglish
The large breaker at the top of the panel that can switch off all the branch circuits. The wires and lugs feeding it stay live even when it is off.
Shop & Trades, Lesson 5.1 (grade 9–12)

main.pyEnglish
A file saved on the Pico that runs automatically every time it powers up.
Electronics & Microcontrollers, Lesson 9.4 (grade 9–12)

mainspringEnglish
A coiled spring that stores energy when a wind-up toy is wound and releases it slowly.
Grade 5 Engineering & Physics, Lesson 9.4 (grade 5)

maintenance logEnglish
A written record of the date, engine hours and work done, with parts used.
Shop & Trades, Lesson 9.5 (grade 9–12) · Fabrics & Sewing II, Lesson 4.1 (grade 6–8)

major diameterEnglish
The largest diameter of a thread, measured over the crests; the nominal size, such as 1/4 in or 8 mm.
Shop & Trades, Lesson 1.2 (grade 9–12)

Manual JEnglish
The ACCA standard method for calculating a home’s heating and cooling loads room by room, used to size equipment.
Shop & Trades, Lesson 6.4 (grade 9–12)

map()English
A microcontroller function that rescales a number from one range to another, such as map(value, 0, 1023, 0, 100) for percent.
Electronics & Microcontrollers, Lesson 7.4 (grade 9–12)

masonryEnglish
Construction of units (brick, stone, concrete block) laid in mortar. Strong in compression, weak in tension.
Architecture & Civil Engineering, Lesson 5.2 (grade 9–12)

mass budgetEnglish
A table of every part’s mass that must add up to less than the allowed total, usually with a margin held in reserve.
Engineering Design, Robotics & Drones, Lesson 1.2 (grade 9–12)

mass flow rate (ṁ)English
How many kilograms of gas pass through the engine each second.
Grade 7 Engineering & Physics, Lesson 7.3 (grade 7)