Physics Vocabulary: Fundamental Science Terms Defined

To read physics well, you need its basic vocabulary. The same words appear when you describe a falling apple, a phone battery, a guitar string, a rainbow, a nuclear reactor, or a black hole. Physics vocabulary names the quantities, laws, and ideas scientists use to explain matter, energy, motion, light, electricity, space, and time. This guide defines core terms from mechanics, energy, thermodynamics, waves, optics, electromagnetism, nuclear physics, quantum mechanics, and relativity for students, self-learners, and anyone building stronger science vocabulary.

Motion, Forces, and Mechanics

Mechanics studies how objects move and how forces change that motion. For many learners, it is the starting point of physics.

Force

A push or pull applied to an object, measured in newtons (N). A force may make something speed up, slow down, turn, or change shape.

Mass

The amount of matter an object contains, measured in kilograms (kg). Mass belongs to the object itself and does not depend on where the object is located.

Weight

The force of gravity acting on mass. The formula is weight = mass × gravitational acceleration, or W = mg. Near Earth's surface, g is about 9.8 m/s².

Velocity

The change in position over time with a stated direction. Because it includes both speed and direction, velocity is a vector quantity.

Acceleration

The change in velocity over time, measured in meters per second squared (m/s²). Acceleration occurs when an object gets faster, gets slower, or changes direction.

Newton's First Law (Inertia)

An object remains at rest, or keeps moving at constant velocity, unless a net external force acts on it. Inertia is the tendency of an object to resist a change in its motion.

Newton's Second Law

The net force on an object equals its mass multiplied by its acceleration: F = ma. A more massive object needs more force to achieve the same acceleration.

Newton's Third Law

Every action force has an equal and opposite reaction force. If a skater pushes backward on the ice, the ice pushes the skater forward with the same size force.

Momentum

Mass multiplied by velocity, written p = mv. In a collision, total momentum is conserved: the combined momentum before the event equals the combined momentum after it.

Friction

A force that resists relative motion between surfaces touching each other. Static friction stops motion from beginning, while kinetic friction acts against motion already happening.

Gravity

The basic attractive force between objects that have mass. Newton's universal law of gravitation says this force grows with the product of the masses and decreases with the square of the distance between them.

Torque

A twisting or turning effect that can rotate an object around an axis. Torque equals the applied force times the perpendicular distance from the axis of rotation.

Work, Power, and Energy

Energy

The ability to do work. Energy appears as kinetic, potential, thermal, electrical, chemical, nuclear, and other forms. Its SI unit is the joule (J).

Kinetic Energy

Energy an object has because it is moving. The formula is KE = ½mv², where m is mass and v is velocity.

Potential Energy

Stored energy that depends on position or arrangement. Gravitational potential energy depends on height, PE = mgh; elastic potential energy is stored when something is stretched or compressed.

Work

Energy transferred when a force moves an object through a distance. Work is W = Fd when the distance is in the direction of the force, and it is measured in joules.

Power

The rate of doing work or transferring energy. Power is P = W/t and is measured in watts (W). One watt is one joule per second.

Conservation of Energy

The principle that energy is not created or destroyed, only converted from one form to another. In an isolated system, the total amount of energy stays constant.

Heat and Thermodynamic Terms

Temperature

A measure of the average kinetic energy of particles in a material. Common temperature scales include Celsius (°C), Fahrenheit (°F), and kelvin (K).

Heat

Thermal energy moving from one object or region to another because of a temperature difference. Heat naturally flows from warmer matter to cooler matter.

First Law of Thermodynamics

Energy cannot be created or destroyed during a thermodynamic process; it only changes form. The change in internal energy equals heat added to the system minus work done by the system.

Second Law of Thermodynamics

For any natural process, the total entropy of an isolated system increases. Heat moves on its own from hot objects to cold ones, not the other way around.

Entropy

A measure of disorder or randomness in a system. Higher entropy means more disorder, and the total entropy of the universe is always increasing.

Conduction

Heat transfer by direct contact between particles. Metals conduct heat well, while materials such as wood and air conduct poorly and act as insulators.

Convection

Heat transfer caused by the motion of a fluid, meaning a liquid or gas. Warm fluid tends to rise and cooler fluid tends to sink, forming convection currents.

Radiation

Heat transfer by electromagnetic waves, with no material medium required. Sunlight warms Earth mainly by radiation.

Specific Heat Capacity

The heat needed to raise the temperature of one kilogram of a substance by one degree Celsius. Water is known for having a particularly high specific heat capacity.

Wave and Sound Vocabulary

Wave

A disturbance that carries energy through space or through matter without permanently moving the matter along with it.

Frequency

The number of full wave cycles that pass each second, measured in hertz (Hz).

Wavelength

The distance from one point on a wave to the next matching point, such as crest to crest. It is usually measured in meters.

Amplitude

The greatest displacement of a wave from its equilibrium position. Larger amplitude generally means the wave carries more energy.

Transverse Wave

A wave whose displacement is at right angles to the direction the wave travels. Light waves are transverse waves.

Longitudinal Wave

A wave whose displacement is parallel to the direction the wave travels. Sound moving through air is a longitudinal wave.

Sound

A mechanical wave created by vibrations and carried through a medium such as air, water, or a solid. Sound does not travel through a vacuum.

Doppler Effect

A change in observed wave frequency when the source and observer move toward or away from each other. A passing train horn seems higher in pitch as the train approaches and lower after it moves away.

Resonance

The strengthening of a vibration when a driving frequency matches a system's natural frequency. Resonance can make a playground swing rise higher, cause a glass to vibrate strongly, or make a bridge oscillate dangerously.

Light, Color, and Optics

Light

Electromagnetic radiation that human eyes can detect, with wavelengths of about 380 nm at the violet end to about 700 nm at the red end.

Reflection

The bouncing of light from a surface. The angle at which light arrives equals the angle at which it reflects.

Refraction

The bending of light when it moves from one medium into another, such as from air into water, because its speed changes.

Diffraction

The bending and spreading of waves as they pass through openings or around obstacles. The effect is strongest when the opening is close to the wavelength in size.

Spectrum

The range of wavelengths in electromagnetic radiation. The visible spectrum includes the rainbow colors: red, orange, yellow, green, blue, indigo, and violet.

Lens

A transparent object, often made of glass, that refracts light so rays come together or spread apart. Convex lenses bring light together; concave lenses spread it out.

Prism

A transparent object, commonly a triangular piece of glass, that uses refraction to split white light into its component colors.

Electricity and Magnetism

Electric Charge

A basic property of matter. Charge can be positive, as in protons, or negative, as in electrons. Like charges repel, and unlike charges attract.

Electric Current

The movement of electric charge through a conductor, measured in amperes (A). A difference in voltage drives current through a circuit.

Voltage (Electric Potential Difference)

The electric "push" that moves current through a circuit, measured in volts (V). It is often compared with water pressure in a pipe.

Resistance

Opposition to the flow of electric current, measured in ohms (Ω). Ohm's Law gives the relationship V = IR, meaning voltage equals current times resistance.

Circuit

A complete path that allows electric current to flow. A circuit includes a power source, conductors, and one or more loads, or devices that use electrical energy.

Magnetic Field

A region where magnetic forces act on moving charges or magnetic materials. Earth's magnetic field is produced by motion in its molten iron core.

Electromagnetic Induction

The production of electric current by a changing magnetic field in or near a conductor. This principle makes electric generators and transformers possible.

Electromagnetic Wave

A traveling wave made of oscillating electric and magnetic fields moving through space at the speed of light. Radio waves, microwaves, visible light, and X-rays are all electromagnetic waves.

The Atomic Nucleus

Radioactivity

The spontaneous release of particles or energy from unstable atomic nuclei. Main types include alpha decay, beta decay, and gamma radiation.

Half-Life

The time it takes for half of a radioactive material to decay. Carbon-14's half-life is about 5,730 years, while radon-222's is about 3.8 days.

Nuclear Fission

The splitting of a heavy atomic nucleus into two or more smaller nuclei, releasing a very large amount of energy. Fission is used in nuclear reactors and atomic weapons.

Nuclear Fusion

The joining of light atomic nuclei to make a heavier nucleus, releasing even more energy than fission. Fusion is the energy source of the Sun and other stars.

Chain Reaction

A self-sustaining series of fission events in which neutrons released by one split nucleus cause more nuclei to split.

Quantum Physics Terms

Quantum

The smallest separate unit of a physical quantity. In quantum mechanics, energy, charge, and other properties occur in discrete packets rather than as fully continuous amounts.

Photon

A quantum, or particle, of light and other electromagnetic radiation. A photon's energy is proportional to its frequency: E = hf, where h is Planck's constant.

Wave-Particle Duality

The idea that particles such as electrons and photons can show both wave behavior and particle behavior, depending on how they are tested.

Uncertainty Principle

Heisenberg's principle that certain pairs of properties, such as position and momentum, cannot both be known with unlimited precision at the same time. Increasing precision in one reduces precision in the other.

Superposition

The principle that a quantum system may exist in several possible states at once until measurement occurs, after which it "collapses" into one state.

Quantum Entanglement

A phenomenon in which two or more particles are linked so that the quantum state of one affects the state of another, no matter how far apart they are.

Space, Time, and Relativity

Special Relativity

Einstein's 1905 theory stating that the laws of physics are the same in all inertial, or non-accelerating, reference frames and that the speed of light is constant for all observers. Its consequences include time dilation and length contraction.

General Relativity

Einstein's 1915 theory explaining gravity as the curvature of spacetime produced by mass and energy, rather than as an ordinary force. General relativity predicts black holes, gravitational waves, and the expansion of the universe.

Spacetime

A four-dimensional structure joining three dimensions of space with one dimension of time. Massive objects bend spacetime, and that bending is experienced as gravity.

Time Dilation

The slowing of time for something moving at high speed relative to an observer, or located in a stronger gravitational field. GPS satellites must correct for time dilation to stay accurate.

E = mc²

Einstein's mass-energy equivalence equation. It says energy (E) equals mass (m) multiplied by the speed of light squared (c²), showing that matter contains an enormous amount of energy.

Gravitational Waves

Ripples in spacetime produced when massive objects accelerate, such as when black holes merge. LIGO directly detected them for the first time in 2015, supporting a prediction of general relativity.

Ways to Learn Physics Terms

• Connect terms to ordinary experience. Walking uses friction, standing involves gravity, and your phone relies on electromagnetic waves.
• Solve physics problems. Terms become clearer when you use them in formulas, calculations, and real situations.
• Learn the core mechanics words first. Force, mass, acceleration, and energy support much of the vocabulary that comes later.
• Use demonstrations. Experiment videos can turn abstract ideas into visible events, making the words easier to remember.
• Study word roots. "Physics" comes from Greek physis, meaning nature. "Thermo-" relates to heat; "electro-" to electricity; "magneto-" to magnets.
• Keep building your wider English vocabulary. Physics overlaps with mathematics, engineering, technology, and the other sciences.

Physics terms give you a practical vocabulary for describing how the physical universe behaves. Once these words feel familiar, textbook questions become easier, but so do everyday observations: why brakes heat up, why colors separate in a prism, why a satellite clock needs correction, and why stars shine. For more word guides and definitions, visit dictionary.wiki.