What is physics? A visual introduction
Physics is the science of matter, energy, space, time and the forces between them. A short visual guide to what it studies, how it works and how to start.
What is physics?
Physics is the science that tries to explain how the universe works at its most basic level: what everything is made of, what moves it, and the rules it follows. It covers everything from a ball rolling down a ramp to the light of distant stars, and it uses mathematics to turn those rules into predictions you can test.
What does physics study?
Almost everything in physics is built from five ideas:
- Matter and mass — what things are made of and how much inertia they have.
- Energy — the capacity to change things. It can change form (motion, heat, light, stored in a spring) but is never created or destroyed.
- Forces — pushes and pulls. There are only four fundamental ones: gravity, electromagnetism, and the strong and weak nuclear forces.
- Space and time — the stage on which everything happens, which relativity shows are linked into a single space-time.
- Waves and fields — how light, sound and forces spread through space.
| Fundamental force | What it does | Acts on |
|---|---|---|
| Gravity | Pulls masses together; shapes planets and galaxies | Everything with mass or energy |
| Electromagnetism | Holds atoms and molecules together; gives light, electricity, magnets | Electric charges |
| Strong nuclear | Binds quarks into protons and neutrons, and nuclei together | Quarks and nuclei |
| Weak nuclear | Drives radioactive decay and fusion in stars | Most subatomic particles |
What are the branches of physics?
| Branch | What it studies | You meet it when… |
|---|---|---|
| Classical mechanics | Motion and forces | you throw a ball or ride a bike |
| Thermodynamics | Heat, temperature, entropy | a cup of tea cools |
| Electromagnetism | Electricity, magnetism, light | you switch on a lamp |
| Optics | How light travels and bends | you use glasses or a camera |
| Quantum mechanics | Atoms and particles | you use a computer chip or LED |
| Relativity | Space, time, gravity, high speeds | your phone finds you by GPS |
| Nuclear & particle physics | Nuclei and elementary particles | you have an X-ray or a PET scan |
| Astrophysics & cosmology | Stars, galaxies, the universe | you look up at night |
How is physics different from other sciences?
Three things: universality (the same laws apply on Earth and in distant galaxies), fundamentality (chemistry, biology and geology ultimately obey physical laws), and mathematical precision (physical theories make numerical predictions — quantum electrodynamics predicts the electron's magnetic moment to about eleven decimal places, and experiment agrees).
How does physics work?
Physics is not a list of facts to memorise; it is a method. Observe something, build a simple model that explains it, use the model to predict something new, then test the prediction. If the test fails, the model is revised or replaced — Newton's gravity held for two centuries until Einstein's relativity explained what it could not.
Theoretical physicists build and refine the models; experimental physicists design the measurements that test them. Both are needed — a theory nobody can test is not yet physics.
Why does physics use so much maths?
Because maths is the language that lets a law make a precise prediction. "Heavier things fall faster" is a guess; tells you exactly how far something falls in any time — and lets you find out you were wrong. You don't need calculus to begin: a lot of physics needs only ratios, graphs and simple algebra.
Where is physics in everyday life?
- Computers and phones exist because quantum physics explained semiconductors; the first transistor was built in 1947.
- GPS works only because engineers correct for relativity: satellite clocks run about 38 microseconds per day fast relative to the ground, and uncorrected the position error would grow by roughly 10 km a day.
- Medical scans use physics directly: MRI uses nuclear magnetic resonance, PET scans detect the light from matter meeting antimatter, X-rays are electromagnetic waves.
- Solar panels rely on the photoelectric effect, which Einstein explained in 1905 — a result that seemed like pure curiosity at the time.
What are common misconceptions about physics?
- "A force is needed to keep something moving." No — an object keeps its velocity unless a force changes it (Newton's first law). Friction is the force that stops things.
- "Heavier objects fall faster." In free fall they all accelerate at the same rate; air resistance is what makes a feather slower.
- "There is no gravity in space." Gravity is only slightly weaker on the space station; astronauts float because they are in free fall.
- "A theory is just a guess." In science, a theory is a well-tested explanation that has survived every attempt to disprove it.
- "Energy gets used up." It changes form (motion into heat, say) but the total is conserved.
How do I start learning physics?
- Play first. Change one number in a simulation and watch what happens — try the Bouncing Ball or the Simple Pendulum.
- Learn the ideas without heavy maths: speed, acceleration, force, energy.
- Add algebra: the equations of motion, projectile motion, Hooke's law.
- Then calculus and vectors, when you want exact answers to harder problems.
- Do one or two problems every day. Physics is learned by doing, not watching.
Frequently asked questions
What is physics in simple words?
What are the main branches of physics?
Do I need to be good at maths to learn physics?
What is the difference between physics and chemistry?
What can you do with physics?
Keep exploring
- Start with motion: How does a ball accelerate toward a target?.
- Then forces and gravity: How does free fall work?.
- Try every experiment: all PhysicsHub simulations.
- A big idea from physics: The three-body problem.