Physics Terms Explained Simply: 60+ Vocabulary for Learners

Physics can seem intimidating to English learners, especially when you’re trying to understand both the science and the vocabulary. When I first started helping ESL students with science subjects, I realised the real barrier wasn’t the concepts — it was the terminology. So I’ve created this guide to explain 60+ physics terms in clear, simple English, with real examples that help the ideas stick.

Whether you’re preparing for an English-medium science exam, writing a research paper, or simply curious about how the world works, You’ll covers the essential vocabulary you need: from fundamental concepts like force and energy to advanced ideas like quantum entanglement and relativity. Each term includes a straightforward definition and practical examples.

Fundamental Physics Concepts

All of physics builds on four fundamental concepts. Understanding these terms is the key to understanding everything else.

Matter

Matter is anything that has mass and takes up space. Everything around you — this screen, the air you breathe, your body — is made of matter. Matter can exist in three states:

State	Definition	Example
Solid	Has a definite shape and volume	Rock, wood, ice
Liquid	Has a definite volume but takes the shape of its container	Water, milk, oil
Gas	No definite shape or volume; fills whatever space it occupies	Oxygen, carbon dioxide, steam

Key related terms:

• Mass 🔊 🎤 — how much matter something contains, measured in kilograms.
• Volume 🔊 🎤 — how much space something takes up, measured in litres or cubic metres.
• Density 🔊 🎤 — mass divided by volume; tells how tightly packed matter is. Water has a density of 1 g/cm³, which is why it’s used as a reference.

Example: Lead is much denser than feathers — a small piece of lead weighs more than a large bag of feathers because its atoms are packed more tightly.

Energy

Energy is the ability to do work or cause change. It can be transferred from one object to another but cannot be created or destroyed (this is the First Law of Thermodynamics).

Two main types:

• Kinetic energy 🔊 🎤 — the energy of movement. A moving ball has kinetic energy. The faster it moves, the more kinetic energy it has.
• Potential energy 🔊 🎤 — stored energy. A ball at the top of a hill has potential energy because of its position; when it rolls down, that potential energy converts to kinetic energy.

Related terms:

• Work 🔊 🎤 — the transfer of energy that occurs when a force acts on an object over a distance. Pushing a shopping trolley across the floor is doing work.
• Power 🔊 🎤 — how fast work is done, measured in watts. A powerful engine does work faster than a weak one.

Example: A hydroelectric dam converts the potential energy of water stored at height into kinetic energy as water flows downward, which then converts to electrical energy.

Force

A force is a push or pull that can change an object’s motion. Forces are measured in newtons and always act in a specific direction.

Important types of force:

• Gravity 🔊 🎤 — pulls objects downward toward Earth. Everything with mass experiences gravity.
• Friction 🔊 🎤 — opposes motion between surfaces. Friction is why a sliding hockey puck eventually stops.
• Inertia 🔊 🎤 — an object’s resistance to change in motion. If something is moving, it wants to keep moving; if it’s stationary, it wants to stay still.
• Tension 🔊 🎤 — the pulling force transmitted through a rope, cable, or string.

Example: When you slam on the brakes in a car, friction between the tyre and road creates the force that slows you down. Without friction, you’d keep sliding.

Motion

Motion is movement through space over time. Four key terms describe motion:

• Speed 🔊 🎤 — how fast an object moves; doesn’t include direction. “The car is going 100 km/h” describes speed.
• Velocity 🔊 🎤 — speed plus direction. “The car is going 100 km/h north” is velocity.
• Acceleration 🔊 🎤 — change in velocity (speed or direction). Pressing the gas pedal accelerates you; pressing the brake pedal is also acceleration (negative acceleration, or deceleration).
• Momentum 🔊 🎤 — mass multiplied by velocity; describes how difficult it is to stop a moving object. A heavy truck moving fast has enormous momentum.

Example: A car driving around a curve at a constant 60 km/h is accelerating because its direction is changing, even though its speed isn’t.

Classical Physics

Classical physics is what most people learn first. It explains how objects move and interact on human scales — from falling balls to orbiting planets.

Newton’s Laws of Motion

Isaac Newton described three fundamental laws that govern how objects move:

1. First Law: Objects at rest stay at rest, and objects in motion stay in motion, unless acted on by a force. This is inertia.
2. Second Law: The more force you apply to an object, the more it accelerates. Written as F = ma (force equals mass times acceleration).
3. Third Law: For every action, there is an equal and opposite reaction. When you jump, you push down on the Earth; the Earth pushes up on you with equal force.

Example: When you’re in a car that suddenly stops, you lurch forward because your body wants to continue moving (First Law). The seat belt applies a force to stop you (Second Law). When you punch a wall, your fist experiences pain because the wall pushes back on your fist with equal force (Third Law).

Thermodynamics

Thermodynamics studies heat and energy transfer. Understanding thermodynamics explains how engines work, why hot drinks cool down, and why the universe is gradually becoming more disordered.

Key concepts:

• Heat 🔊 🎤 — energy transfer between objects at different temperatures. Heat always flows from hotter to cooler objects.
• Temperature 🔊 🎤 — a measure of how fast particles are moving in a substance. Higher temperature means faster particle motion.
• Entropy 🔊 🎤 — a measure of disorder or chaos in a system. As entropy increases, energy becomes less useful; this is why everything tends toward disorder (the Second Law of Thermodynamics).
• The First Law of Thermodynamics: Energy cannot be created or destroyed, only transferred or transformed.
• The Second Law of Thermodynamics: Heat flows from hot to cold, and entropy always increases in an isolated system.

Example: When you put a hot cup of coffee in a cool room, heat flows from the coffee into the room until they reach the same temperature. This process increases entropy — the ordered energy of the hot coffee becomes spread out and disordered throughout the room, making it impossible to recover that heat to make the coffee hot again.

Electromagnetism

Electromagnetism deals with electric and magnetic forces and how they interact with matter.

Key terms:

• Electric charge 🔊 🎤 — a fundamental property of matter. Charges can be positive or negative; opposite charges attract, like charges repel.
• Electric field 🔊 🎤 — the region around an electric charge where the charge exerts a force on other charges.
• Magnetic field 🔊 🎤 — the region around a magnet where magnetic forces operate. Invisible but detectable with a compass.
• Electromagnetic waves 🔊 🎤 — waves made of electric and magnetic fields oscillating together. Light is an electromagnetic wave, as are radio waves, microwaves, and X-rays.

Example: When you move a magnet near a compass, the compass needle points toward the magnet because the compass responds to the magnetic field surrounding it.

Modern Physics

Modern physics includes quantum mechanics and relativity — revolutionary theories that changed how we understand reality at very small and very large scales.

Quantum Mechanics

Quantum mechanics describes the behaviour of particles at atomic and subatomic scales. The rules here are very different from everyday physics.

Key ideas:

• Superposition 🔊 🎤 — a quantum particle can exist in multiple states simultaneously until it is observed or measured. An electron can be in multiple places at once.
• Uncertainty principle 🔊 🎤 — you cannot simultaneously know both a particle’s exact position and exact momentum. The more precisely you measure one, the less you know about the other.
• Wave-particle duality 🔊 🎤 — particles like electrons sometimes behave like waves and sometimes like particles, depending on how you measure them.
• Quantum entanglement 🔊 🎤 — when two particles become linked so that measuring one instantly affects the other, no matter how far apart they are. Einstein called this “spooky action at a distance.”

Example: In quantum mechanics, an electron doesn’t have a definite position like a marble on a table. Instead, it exists as a probability cloud — it could be here, or there, or anywhere in the cloud until you measure it.

Relativity

Einstein’s theory of relativity shows that space and time are not absolute — they’re relative to the observer.

Special Relativity (1905) deals with motion at high speeds:

• Time dilation 🔊 🎤 — time passes slower for objects moving at high speeds. If you travel at nearly the speed of light, you age slower than people on Earth.
• Length contraction 🔊 🎤 — objects shorten in the direction of motion at high speeds.
• E = mc² — mass and energy are equivalent; a small amount of mass can be converted into enormous amounts of energy (this is how nuclear power works).

General Relativity (1915) explains gravity as curved space:

• Massive objects like the Earth and Sun curve space and time around them.
• Objects follow the curves in space, which we perceive as gravity.
• Light bends around massive objects because it follows the curves in space.
• Black holes are regions where space is so curved that not even light can escape.

Example: GPS satellites must account for both special and general relativity. Time passes slightly faster for satellites in orbit than for people on Earth, so without relativistic corrections, GPS would be off by several kilometres per day.

Applied Physics Fields

These areas of physics deal with practical applications and specific domains.

Thermodynamics Revisited: Practical Applications

Thermodynamics explains:

• Why engines convert heat into motion
• Why refrigerators move heat from cold to hot (using energy)
• Why the universe is gradually becoming more disordered (entropy always increases)

Particle Physics

Elementary particles 🔊 🎤 are the smallest building blocks of matter:

• Quarks 🔊 🎤 — fundamental particles that make up protons and neutrons.
• Electrons 🔊 🎤 — negatively charged particles that orbit atoms.
• Photons 🔊 🎤 — particles of light and electromagnetic radiation.
• Higgs boson 🔊 🎤 — the particle that gives other particles mass (discovered in 2012).

Example: Everything you see is made of quarks (in protons and neutrons) and electrons. The table you’re sitting at is almost entirely empty space, with tiny nuclei surrounded by electron clouds.

Nuclear Physics

Nuclear physics studies atomic nuclei:

• Fission 🔊 🎤 — splitting a heavy atom (like uranium) releases enormous energy. This is how nuclear power plants and nuclear weapons work.
• Fusion 🔊 🎤 — joining light atoms (like hydrogen) to form heavier atoms also releases enormous energy. This is how the Sun produces energy and is the goal of future clean energy.
• Radioactivity 🔊 🎤 — unstable atoms emit radiation as they decay into more stable forms.

Example: A nuclear power plant uses the heat from nuclear fission to boil water into steam, which turns turbines to generate electricity — essentially a very hot kettle.

Common Mistakes with Physics Terms

✗ Incorrect: “The object has more velocity because it’s moving faster.”

✓ Correct: “The object has more speed because it’s moving faster. Its velocity is different if the direction changes.”

Why: Velocity includes direction; speed does not. They’re not interchangeable.

✗ Incorrect: “Heat rises because it’s lighter than air.”

✓ Correct: “Warm air rises because heat transfer causes air to expand, making it less dense, so it floats upward.”

Why: Heat doesn’t have weight — it’s energy transfer. Hot air rises because of density differences.

✗ Incorrect: “When you accelerate, you’re always speeding up.”

✓ Correct: “Acceleration is any change in velocity, including slowing down or changing direction.”

Why: In physics, acceleration has a specific technical meaning that includes any change in motion.

Sample Dialogue: Physics Concepts in Class

Physics Vocabulary Study Tips

From my experience teaching ESL students physics vocabulary, here are three strategies that work:

Tip 1: Understand the Concept Before the Term

Don’t try to memorise definitions. Instead, understand what the concept describes, then the word will make sense. “Momentum” is easier to learn if you first understand why a truck is harder to stop than a bicycle.

Tip 2: Use Analogies from Everyday Life

Connect physics terms to things you experience. Energy is like money — you can spend it, save it, or exchange it. Entropy is like a messy room — it naturally becomes more disordered unless you do work to organise it.

Tip 3: Create a Visual Physics Vocabulary Chart

Make a chart with three columns: Term, Simple Definition, Real-World Example. Reviewing this regularly helps the vocabulary stick.

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• ↑ Back to pillar: English Vocabulary (Topical)

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