Physics Glossary
314 terms, each with a plain definition, technical definition, example and the confusion it usually causes.
A
Absolute Zero
The coldest anything can possibly be — 0 kelvin (−273.15°C) — where particles have the min…
Acceleration
How quickly velocity changes. Speeding up, slowing down, and turning are all accelerations…
Acoustic Impedance
How much a material resists the passage of sound — the reason echoes form where two materi…
Actuator
The muscle of a machine — a device that turns an electrical signal into physical movement,…
Adiabatic Process
A change with no heat entering or leaving the system — temperature changes come purely fro…
Aliasing
When fast motion looks wrong on camera — wagon wheels appearing to spin backwards in old m…
Alternating Current (AC)
Electric current that flows back and forth, reversing direction many times per second — wh…
Ammeter
An ammeter measures electric current — the actual flow of charge. It must become part of t…
Ampère's Law
The magnetic twin of Gauss's law: the magnetic field looping around a wire depends only on…
Amplitude
How big a wave's oscillations are — measured from the middle line to the top of a crest.…
Angular Momentum
The rotational equivalent of momentum — a measure of how much ‘spin’ an object has, combin…
Angular Velocity
How fast something is spinning — the rate at which its angle changes, measured in radians …
Antinode
The point on a standing wave that swings with the biggest motion — halfway between two nod…
Archimedes' Principle
The buoyant force on a submerged object equals the weight of the fluid it displaces — why …
Atwood machine
An Atwood machine is a pulley with a different mass hanging on each side — a classic lab s…
B
Banked curve
A banked curve is a road or track tilted inward so part of the normal force points toward …
Battery
A device that stores energy chemically and releases it as electricity on demand — from pho…
Beats (Waves)
The slow wah-wah pulsing heard when two almost-identical notes play together — piano tuner…
Bernoulli's principle
The rule that faster-moving fluid exerts lower pressure. It is the key idea behind airplan…
Big Bang
The hot, dense beginning of our universe 13.8 billion years ago — space itself expanding f…
Binding energy
The energy that holds a nucleus together — equivalently, the energy you would need to supp…
Biot–Savart Law
The recipe for the magnetic field of any current shape — add up the tiny field contributio…
Blackbody
An idealized perfect absorber and emitter of radiation — the theoretical standard for how …
Bose–Einstein Statistics
The rulebook for sociable particles — photons and helium-4 atoms love crowding into the sa…
Boundary Layer
The thin skin of slow-moving fluid hugging every surface — the reason golf balls have dimp…
Brewster's Angle
The special angle where reflected light becomes perfectly polarized — used in sunglasses a…
Buoyancy
The upward push a fluid gives to anything immersed in it. It is why boats float, beach bal…
C
Capacitance
How much electric charge a device can store per volt — the measure of a capacitor's storag…
Capillary Action
How water climbs up narrow tubes against gravity — the physics behind paper towels soaking…
Carnot Cycle
The ideal, most efficient possible heat engine cycle — the theoretical limit no real engin…
Cavitation
When low pressure boils water cold — collapsing vapor bubbles that chew up boat propellers…
Center of Mass
The single point where an object's entire mass can be considered concentrated for analyzin…
Centripetal Acceleration
The inward-pointing acceleration that keeps an object moving in a circle — constantly chan…
Chromatic Aberration
The color fringing in cheap lenses — different colors focus at different points because gl…
Coherence (Optics)
How 'in step' a light wave is — laser light is highly coherent, which is why it paints cri…
Coherent source
Coherent sources are wave sources that march in lockstep — same frequency and a fixed phas…
Complex Number
A number with real and imaginary parts (a + bi) — essential for AC circuits, quantum mecha…
Compton effect
The Compton effect is X-rays bouncing off electrons and losing energy — proof that light c…
Concave Lens
A lens thinner in the middle that spreads light rays apart — always giving smaller, uprigh…
Concave Mirror
A mirror curved inward like a bowl — it can focus light to a point, magnify, or project re…
Conduction
Heat traveling through direct contact — molecule bumping into molecule, passing energy alo…
Convection
Heat carried by moving fluid — hot air or water rises, cool fluid sinks, and the circulati…
Convex Lens
A lens thicker in the middle that converges light rays — the magnifying glass lens.…
Coordinate system
The grid and rules you lay over space to say where things are — like choosing where 'zero'…
Coriolis Effect
The apparent curving of moving air and water caused by Earth's rotation — hurricanes spin …
Cosmic Microwave Background
The afterglow of the Big Bang — faint microwaves arriving from every direction, the oldest…
Coulomb (Unit)
The unit of electric charge — about 6.24 × 10¹⁸ electrons make one coulomb.…
Coupled Pendulum
Two pendulums linked by a spring that trade energy back and forth — set one swinging and t…
Critical Point
The temperature and pressure above which liquid and gas become indistinguishable — a singl…
Cross Product
A way to multiply vectors that gives a new vector perpendicular to both — the math behind …
CT Scan
A 3D X-ray — hundreds of X-ray snapshots from all angles, computed into cross-sectional sl…
D
Dark Matter
The invisible stuff outweighing all visible matter 5-to-1 — detected only by its gravity h…
de Broglie wavelength
The de Broglie wavelength is the wavelength assigned to matter — every moving particle, fr…
Density
How much mass is packed into a given volume. A bowling ball and a beach ball can be the sa…
Derivative
The instantaneous rate of change of something — how fast it is changing at one exact momen…
Diamagnetism
Weak repulsion from magnets — even water and frogs are slightly diamagnetic, and strong en…
Dielectric
An insulating material placed between capacitor plates that boosts how much charge the cap…
Differential Equation
An equation involving rates of change — the language physics uses to describe how things e…
Diffraction
Waves bending and spreading around obstacles and through narrow openings — why you can hea…
Diffraction Grating
A surface with thousands of fine parallel lines that splits light into its rainbow spectru…
Dimensional Analysis
Checking physics with units — a powerful method to verify formulas, catch errors, and even…
Diode
A one-way valve for electric current — lets it flow forward, blocks it backward.…
Dispersion
White light splitting into a rainbow because different colors bend by different amounts in…
Dispersion (Waves)
Why prisms make rainbows — different colors travel at slightly different speeds in glass, …
Displacement
The straight-line change in position from start to finish — how far you ended up from wher…
Divergence
How much a vector field spreads out from a point — positive where field lines are born (li…
Doppler Effect
The change in observed pitch (or color) of waves when the source and observer move toward …
Dot Product
A way to multiply vectors that gives a single number — measuring how much two vectors ‘agr…
Drag
The resistance a fluid puts up against something moving through it — the reason you feel p…
Drag Coefficient
A single number rating how aerodynamic a shape is — a sleek car scores ~0.25, a brick ~2.0…
Driven Oscillation
A vibration kept going by repeated pushes — pushing a swing at just the right moment each …
Drone
An unmanned aircraft — most commonly a quadcopter — that stays aloft and maneuvers using s…
E
Echo
An echo is a sound wave bouncing off a distant surface and returning to your ears — nature…
Eddy Current
Swirling loops of current induced inside chunks of metal by changing magnetic fields — use…
Efficiency
How much of the energy you put into a machine comes out as useful work — the rest is waste…
Eigenvalue
A matrix's special scaling numbers — along eigenvector directions, the matrix stretches bu…
Eigenvector
The special directions a transformation leaves pointing the same way — merely stretched or…
Elastic Collision
A collision in which both momentum AND kinetic energy are conserved — the objects bounce a…
Electric Charge
The property of matter that causes electric forces — positive and negative charges attract…
Electric Circuit
A complete loop that lets charge flow — a path from a power source, through components, an…
Electric Current
The flow of electric charge — how many coulombs pass a point every second.…
Electric Field
The invisible zone of influence around any charge — the region where another charge would …
Electric motor
A device that turns electrical energy into motion — the thing spinning inside fans, electr…
Electric Potential
The electrical ‘height’ at a point in space — how much potential energy each unit of charg…
Electrical Grounding
Connecting a circuit or appliance to the Earth so stray electricity has a safe escape path…
Electromagnetic Induction
Making electricity from magnetism — moving a magnet near a wire (or a wire near a magnet) …
Electromagnetic Spectrum
The full family of light — from long radio waves through visible light to short gamma rays…
Electronvolt
A tiny unit of energy used for atoms, particles, and light. One electronvolt is the energy…
Enthalpy
The accountant's energy — internal energy plus the energy cost of making room (pressure × …
Entropy
A measure of disorder — or more precisely, of how spread out and unusable energy has becom…
Error Analysis
The honest accounting of uncertainty in measurements — how wrong your result might be, and…
Escape Velocity
The minimum speed an object needs to break free from a planet's gravity forever, without f…
Evanescent Wave
A wave that fades exponentially instead of traveling — it appears just past a boundary dur…
Event Horizon
The point of no return around a black hole — cross it and not even light can escape back o…
Exponential (Function)
Growth or decay where the rate is proportional to the current amount — the mathematics of …
F
Fabry–Pérot Interferometer
Two ultra-parallel mirrors bouncing light hundreds of times — the sharpest color filter in…
Faraday's Law
The rule that a changing magnetic field creates electricity — the principle behind every g…
Fermi–Dirac Statistics
The rulebook for antisocial particles — electrons refuse to share a quantum state, which i…
Ferromagnetism
The strong magnetism of iron, nickel, and cobalt — their atomic magnets spontaneously alig…
Fiber Optic
A hair-thin glass strand that guides light over kilometers using total internal reflection…
Fiber optics
Hair-thin strands of glass that carry information as pulses of light, bouncing the light a…
Fluid Dynamics
The study of fluids in motion — from airflow over wings to blood in arteries to weather sy…
Fluid Statics
The study of fluids at rest — pressure, buoyancy, and why dams are thicker at the bottom.…
Focal Length
How strongly a lens or mirror bends light — the distance from the lens to the point where …
Force
A push or a pull on an object. Forces can start motion, stop motion, change direction, or …
Fourier Series
Building any repeating wave from pure sine waves — the mathematics behind MP3s and musical…
Fourier Transform
The mathematical prism that splits any signal into its pure frequencies — how noise-cancel…
Free-Body Diagram
A simple sketch showing an object alone with arrows for every force acting on it — the ess…
Frequency
How many wave cycles pass a point every second. Higher frequency means more cycles per sec…
Fresnel Equations
How much light reflects versus transmits at a boundary — why windows show your reflection …
G
Galvanometer
The ancestor of every analog meter — a tiny current twists a coil in a magnetic field, swi…
Gauss's Law
A shortcut for electric fields: the total electric flux through any closed surface equals …
Gibbs Free Energy
The 'will it happen on its own?' energy — if Gibbs free energy drops, the process can run …
Gluon
The particle that glues quarks together — carriers of the strong force that themselves car…
GPS
The Global Positioning System — the satellite network your phone uses to figure out exactl…
Gradient
The arrow pointing steepest uphill — temperature's gradient tells heat which way to flow.…
Gravitational Field
The invisible influence a mass creates in the space around it — any other mass placed ther…
Gravitational Potential
The potential energy per kilogram at a point in a gravitational field — the energy you wou…
Gravitational Wave
Ripples in spacetime itself from colliding black holes — first directly heard by LIGO in 2…
Group Velocity
The speed at which a pulse of waves — and its energy — actually travels, which can differ …
H
Half-life
The time it takes for half of a sample of radioactive material to decay. After one half-li…
Hall Effect
How we measure magnetic fields with a chip — current bent sideways by a magnet builds up a…
Harmonic
One of the pure tones that combine to make a complex sound — whole-number multiples of the…
Heat
Energy moving from a hotter object to a colder one because of the temperature difference.…
Heat capacity
Heat capacity tells you how stubborn a substance is about changing temperature — how much …
Heat Death of the Universe
The universe's far-future fate in current theory — everything spread so evenly that no usa…
Heat Engine
Any device that turns heat flowing from hot to cold into useful work — from steam engines …
Heat Pump
A device that moves heat from cold to hot — a refrigerator run in reverse to heat your hom…
Heisenberg Picture
Quantum mechanics with the operators moving instead of the states — mathematically equal t…
Higgs Boson
The particle discovered at CERN in 2012 — a ripple in the Higgs field that fills space and…
Hohmann Transfer
The most fuel-efficient way to move between two circular orbits — an elliptical path that …
Hologram
A 3D image recorded and reconstructed with laser light — capturing not just brightness but…
Hydraulic Press
A machine that multiplies force using fluid pressure — a small push on a small piston beco…
Hydrostatic Pressure
The pressure in a still fluid that grows with depth — why your ears pop diving deep.…
Hysteresis
When a material 'remembers' its magnetic past — magnetize iron and some magnetism lingers …
I
Impulse
The effect of a force applied over time — a big force for a short time can equal a small f…
Impulse (Physics)
The total 'shove' delivered by a force over time — a big force for a short time can equal …
Inelastic Collision
A collision where the objects stick together or deform — momentum is conserved, but some k…
Inertia
The tendency of objects to keep doing what they are already doing — staying still if still…
Infrasound
Sound waves too low for human hearing — below about 20 Hz — produced by earthquakes, volca…
Integral
The reverse of a derivative — it adds up tiny pieces to find a total. The integral of velo…
Isobaric Process
A thermodynamic change at constant pressure — like heating gas in a cylinder with a freely…
Isochoric Process
Heating or cooling at constant volume — like a sealed pressure cooker: nothing expands, so…
Isothermal Process
A process that happens at constant temperature — the system stays in thermal balance with …
J
Jerk
Jerk is the rate at which acceleration itself changes — the jolt you feel when a car start…
Jones Vector
A compact two-number label for a light wave's polarization — the math behind LCD screens a…
Josephson Junction
Two superconductors separated by a whisper-thin insulator — quantum tunneling lets current…
K
Kilowatt-Hour
The unit on your electricity bill — the energy used by running a 1000-watt appliance for o…
Kinetic Friction
The steady resisting force that opposes motion while an object is already sliding across a…
Kirchhoff's laws
Kirchhoff's two laws are the bookkeeping rules of circuits: charge can't pile up at a junc…
L
Lagrangian Point
Parking spots in space where the gravity of two bodies plus orbital motion balance out — t…
Laminar flow
Smooth, orderly fluid flow where the fluid moves in parallel layers that slide past each o…
Laplace Transform
Turning calculus into algebra — it converts differential equations into solvable algebraic…
Laser
Light Amplification by Stimulated Emission of Radiation — an intense, single-color, perfec…
Laser Speckle
The grainy shimmer in laser light — random interference from rough surfaces, the bane of l…
Latent Heat
The hidden heat absorbed or released during a phase change — it breaks or forms molecular …
LED
Light-Emitting Diode — a semiconductor that converts electricity directly into light, far …
Lens
A curved piece of glass or plastic that bends light to focus it — the heart of cameras, gl…
Lenz's Law
Nature's ‘push back’ rule: induced currents always flow in the direction that opposes the …
LiDAR
Radar with laser light — self-driving cars paint the world in 3D with millions of light pu…
Lift Coefficient
A wing's efficiency number — how much lift a wing shape generates per unit of airflow.…
Logarithm
The inverse of exponentiation — it answers ‘to what power?’ and tames quantities spanning …
Longitudinal Wave
A wave where the medium vibrates back and forth along the same direction the wave travels …
Lorentz Force
The combined push on a charged particle from electric and magnetic fields — the force behi…
M
Mach Number
How fast something moves compared to the speed of sound — Mach 2 means twice the speed of …
Magnetic Dipole
The basic unit of magnetism — every magnet, from a compass needle to an electron, is a dip…
Magnetic Field
The invisible influence around magnets and moving charges that pushes on other magnets and…
Magnetic Flux
How much magnetic field passes through a surface — the quantity whose change creates elect…
Magnification
Magnification tells you how much bigger (or smaller) an image is than the object — a micro…
Malus's Law
How polarizing filters dim light — two crossed polarizers block everything; at an angle θ …
Manometer
A U-shaped tube of liquid that measures pressure by the height difference between its two …
Mass
How much matter an object contains. Mass is what makes things hard to push around and what…
Maxwell Relations
Four elegant equations linking quantities you can't measure (like entropy change with volu…
Mechanical Advantage
How much a machine multiplies your force — a pulley system with mechanical advantage 4 let…
Michelson Interferometer
A beam-splitter and two mirrors that detect absurdly tiny distance changes — LIGO is a gia…
Mirror
A smooth reflective surface that forms images by bouncing light — flat mirrors show you yo…
Moiré Pattern
The strange wavy bands that appear when two fine grids overlap — like filming a striped sh…
Moment of Inertia
An object's resistance to changes in its rotation — the rotational equivalent of mass.…
Momentum
How much 'oomph' a moving object carries — it depends on both mass and velocity. Heavy, fa…
MRI
Magnetic resonance imaging — the hospital scanner that takes detailed pictures of soft tis…
Muon
A heavy, short-lived cousin of the electron — born from cosmic rays, living 2.2 microsecon…
N
Nanotechnology
Engineering at the scale of atoms and molecules (1–100 nm) — where materials gain surprisi…
Navier–Stokes Equations
The master equations of fluid flow — Newton's second law written for every drop of fluid. …
Neutrino
The ghost particle — nearly massless, chargeless, and so aloof that trillions pass through…
Newton's Rings
Rainbow rings where a lens touches glass — thin-film interference made visible, used to te…
Node (Wave)
A point on a standing wave that never moves — where the two traveling waves always cancel …
Normal Force
The push a surface exerts on an object resting on it, always directed perpendicular (norma…
Nuclear Binding Energy
The energy holding an atomic nucleus together — the ‘glue’ energy you would need to split …
Nuclear fission
The splitting of a heavy atomic nucleus into two lighter nuclei, releasing a large burst o…
Nuclear fusion
The joining of two light atomic nuclei into a heavier one, releasing energy. This is the r…
Nutation
The small nodding wobble on top of precession — a spinning top's axis traces tiny loops as…
Nyquist Frequency
The highest frequency you can faithfully record — exactly half your sampling rate. Sample …
O
Octave
The musical interval between a note and another with exactly double (or half) its frequenc…
Ohmmeter
An ohmmeter measures electrical resistance directly — dial it to Ω, touch the probes to a …
Orbital Mechanics
The physics of satellites and planets — orbits are continuous falling, where forward speed…
Order of magnitude
A rough size estimate to the nearest power of ten — answering 'about how big?' instead of …
P
Paramagnetism
Weak attraction to magnets — materials like aluminum whose atoms carry unpaired electrons …
Partition Function
The master key of statistical mechanics — one sum over all possible states that unlocks en…
Pascal
The SI unit of pressure. One pascal is one newton of force spread over one square meter — …
Pauli Exclusion Principle
No two electrons in an atom may share the exact same quantum address — the rule that build…
Period
The time one complete wave cycle — or one full back-and-forth oscillation — takes.…
PET Scan
Imaging metabolism itself — a radioactive sugar tracer lights up hungry tissues like tumor…
Phase (Wave)
A wave's position within its cycle — telling you whether it is at a crest, trough, or some…
Phase Change
When matter switches state — melting, freezing, boiling, condensing — absorbing or releasi…
Phase Velocity
The speed at which a single wave crest moves — distinct from the speed of the overall puls…
Photon
The smallest possible packet of light — a single particle of electromagnetic energy. When …
Piezoelectric Effect
Squeeze certain crystals and they produce electricity — feed them electricity and they cha…
Pitot Tube
The little probe on aircraft wings that measures airspeed by comparing ram pressure to sta…
Planck Length
The shortest meaningful distance in physics — about 10⁻³⁵ m, where quantum gravity takes o…
Polarization
Filtering light so its waves vibrate in only one direction — how polarized sunglasses kill…
Positron
The electron's antimatter twin — same mass, opposite charge; when it meets an electron, bo…
Power
How fast work gets done — the rate at which energy is transferred or converted.…
Precession
The slow circling of a spinning axis — a tilted spinning top does not fall over; instead i…
Pressure
How concentrated a force is over an area. The same push hurts more through a sharp pin tha…
Projectile
Any object thrown, launched, or dropped that moves under gravity's influence (ideally with…
Q
Quality Factor (Q)
How 'pure' an oscillator is — a high-Q tuning fork rings for ages, while a low-Q car suspe…
Quantum
The smallest indivisible chunk of something — like energy or light — that nature allows. A…
Quantum Number
The set of numbers that completely describes an electron's state in an atom — its address …
Quantum Tunneling
Particles leaking through barriers they classically couldn't climb — the reason the Sun sh…
Quark
The tiny building blocks inside protons and neutrons — six types that combine to make most…
R
Radar
Finding things with radio echoes — from air-traffic control to your car's blind-spot warni…
Radian
The natural unit for measuring angles in physics — based on the circle itself rather than …
RC Circuit
A circuit with a resistor and capacitor in series — the classic example of something that …
Real Image
An image formed where light rays actually meet — it can be projected onto a screen.…
Recoil
Recoil is the backward kick you feel when something shoots forward — a gun firing a bullet…
Redshift
The stretching of light to longer (redder) wavelengths from receding objects — how we know…
Reflection
Light bouncing off a surface — the reason you can see yourself in a mirror.…
Refraction
Light bending as it passes from one material into another — why a straw looks broken in a …
Relativity
The idea that measurements of space and time depend on how the observer is moving. There i…
Renewable energy
Energy from sources that nature replenishes — sunlight, wind, flowing water, Earth's heat,…
Resistance
How much a material opposes the flow of electric current — the electrical equivalent of fr…
Resolving power
Resolving power is an instrument's ability to see two close objects as separate instead of…
Resonance
When you push something at exactly its natural rhythm, small pushes add up into huge oscil…
Resonance (Physics)
When pushes timed to a system's natural rhythm build enormous motion — a singer shattering…
Reynolds Number
The dimensionless number predicting whether fluid flow is smooth (laminar) or chaotic (tur…
Right-Hand Rule
A hand gesture that tells you the direction of magnetic forces and fields — point fingers,…
RMS Voltage
The ‘effective’ voltage of an AC supply — the DC voltage that would deliver the same power…
Rolling Motion
Rotation plus translation at once — a rolling wheel's bottom point is instantaneously at r…
Rotational Kinetic Energy
The energy stored in spinning — a flywheel keeps its energy in rotation the way a moving c…
S
Satellite
Any object orbiting a planet — the Moon is natural, while the thousands of human-made sate…
Scalar
A quantity described by a single number with no direction — like temperature (25°C), mass …
Schrödinger Equation
The master equation of quantum mechanics — it dictates how the quantum wave describing a p…
Scientific notation
A compact way to write very big or very small numbers as a number between 1 and 10 times a…
Semiconductor
A material — like silicon — whose ability to conduct electricity sits between a conductor …
Sensor
A device that detects something in the physical world — light, motion, temperature, pressu…
Shock Wave
A violent, abrupt pressure wave created when something moves faster than the speed of soun…
Signal Processing
The art of cleaning and reading signals — from sharpening phone photos to pulling exoplane…
Significant figures
The digits in a measurement that actually mean something — every digit you are sure about,…
Simple Harmonic Motion (SHM)
The purest back-and-forth vibration — a mass on a spring, or a pendulum swinging through s…
Simple Pendulum
A mass hanging from a string or rod that swings back and forth — the classic example of pe…
Siphon
Draining a tank over its rim with a bent tube — once started, gravity and air pressure kee…
Slope
How steep a line is — the ratio of vertical change to horizontal change. On a physics grap…
Snell's Law
The bending rule for light entering a new material — it bends toward the normal when slowi…
Solar Cell
A device that converts sunlight directly into electricity using the photovoltaic effect in…
Solenoid
A coil of wire wound into a helix — when current flows, it acts like a bar magnet with a n…
Sonar
Seeing with sound underwater — how submarines, dolphins, and fish-finders navigate the dar…
Spacetime
The four-dimensional fabric combining the three dimensions of space with time as a fourth …
Specific Heat Capacity
How much heat energy it takes to raise 1 kg of a substance by 1 degree — water needs a lot…
Spherical Aberration
Blurring caused by a spherical lens or mirror focusing edge rays and center rays at differ…
Spring Constant
A number that measures a spring's stiffness — how much force is needed to stretch or compr…
Standard Model
Physics' best theory of the subatomic world — the complete catalog of fundamental particle…
Standing Wave
A wave pattern that appears frozen in place — with still points (nodes) and wildly vibrati…
Standing Wave Ratio
A measure of how much of a wave reflects back at a boundary — 1:1 means perfect transmissi…
Static Equilibrium
The state of an object that is completely at rest, with all forces and all torques balance…
Static Friction
The grip-like force that keeps an object from starting to slide — it matches your push exa…
Streamline
An imaginary line drawn through a flowing fluid showing the path the fluid follows — like …
Strong Nuclear Force
The most powerful force in nature — it glues quarks together and holds atomic nuclei toget…
Superconductivity
When certain materials cooled near absolute zero conduct electricity with literally zero r…
Superconductor
A material that conducts electricity with exactly zero resistance when cooled below a crit…
Superposition
When two or more waves meet, their displacements simply add up — crest on crest makes a bi…
Surface tension
The invisible 'skin' on the surface of a liquid that lets water striders walk on ponds and…
Sympathetic Vibration
When one vibrating object sets another tuned object singing without touching it — strike o…
T
Taylor Series
Approximating curvy functions with simple polynomials — how physicists tame sines, cosines…
Temperature
How hot or cold something is — a measure of the average kinetic energy of its particles.…
Tension
The pulling force transmitted through a rope, cable, or string when it is pulled tight at …
Tensor
A generalization of scalars, vectors, and matrices — stress, inertia, and spacetime curvat…
Thermal Conductivity
How well a material conducts heat — high for metals, low for insulators like wood or foam.…
Thermal Equilibrium
When two objects in contact reach the same temperature and heat stops flowing between them…
Thermal expansion
Thermal expansion is the tendency of matter to grow slightly larger when heated — the reas…
Thermal Radiation
Heat traveling as invisible infrared light — the only heat transfer that works through emp…
Thermocouple
A thermometer made of two joined wires — heat the junction and it generates a tiny voltage…
Thin-Film Interference
The rainbow colors in soap bubbles and oil slicks — light waves reflecting off the film's …
Tidal Force
The stretching force from gravity being stronger on one side of a body than the other — wh…
Timbre
The ‘color’ of a sound — what makes a piano and a violin sound different even playing the …
Torque
The turning effect of a force — what makes wrenches, doorknobs, and seesaws work. Push far…
Torque (Physics)
The twisting effect of a force — how hard you turn a wrench depends on the force AND how f…
Total Internal Reflection
When light trying to leave a dense material hits the boundary at too shallow an angle and …
Transformer
A device that steps AC voltage up or down using two coils and a shared magnetic field — th…
Transistor
A tiny electronic switch and amplifier — the building block of every computer chip, with b…
Transverse Wave
A wave where the medium vibrates side to side, perpendicular to the direction the wave tra…
Trigonometry
The mathematics of triangles — especially right triangles — used in physics to split vecto…
Triple Point
The unique temperature and pressure where solid, liquid, and gas phases of a substance coe…
Turbulent flow
Chaotic, swirling fluid flow full of eddies and mixing — like whitewater rapids or the gus…
U
Ultrasound
Sound waves too high-pitched for human ears — above about 20,000 Hz — used in medical imag…
Ultrasound Imaging
Seeing babies and hearts with sound — safe, real-time echoes at frequencies far above hear…
Uncertainty principle
The rule that you cannot know both a particle's exact position and its exact momentum at t…
V
Variable mass
Variable mass means the mass of the moving object itself changes over time — most famously…
Vector
A quantity that has both a size and a direction — like velocity (60 km/h north) or force (…
Velocity
Speed with a direction attached. 60 km/h north is a velocity; 60 km/h by itself is only a …
Venturi Effect
Fluid speeds up through a narrow spot and its pressure drops — the trick behind carburetor…
Virtual Image
An image that looks like it is somewhere the light never actually goes — like your reflect…
Viscosity
A fluid's resistance to flowing — its 'thickness.' Honey has high viscosity and pours slow…
Voltage
The electrical 'push' — how much energy each unit of charge carries as it flows through a …
Voltmeter
A voltmeter measures voltage — the electrical pressure difference between two points. It c…
W
Water Hammer
The bang in pipes when a tap slams shut — the water column's momentum converts into a pres…
Wave Speed
How fast a wave disturbance travels through a medium — not how fast the medium itself move…
Wave-particle duality
The strange fact that light and matter sometimes act like waves and sometimes like particl…
Wavefront
An imaginary surface connecting all points of a wave that are oscillating in step — like t…
Waveguide
A pipe that channels waves — fiber-optic cables are waveguides for light, and microwave ov…
Wavelength
The distance between one wave crest and the next — the length of a single complete wave cy…
Weak Nuclear Force
The force behind radioactive decay — it can change one type of particle into another, powe…
Wheatstone Bridge
A clever circuit that measures unknown resistance by balancing — when the middle meter rea…
Work
Energy transferred by a force pushing something through a distance. No movement, no work —…
Work–Energy Theorem
The net work done on an object equals its change in kinetic energy — push something and th…