From a falling apple to a galaxy spinning through space, physics is the science that explains why the universe behaves the way it does.
On 25 November 1915, Albert Einstein presented a set of four short papers to the Prussian Academy of Sciences in Berlin. In them, he described gravity not as a force pulling objects together, but as the bending of space and time itself. It sounds abstract — yet that single idea now underpins GPS satellites, black hole imaging, and our entire understanding of the universe. That is physics: the discipline that takes questions as simple as "why does an apple fall?" and follows them all the way to the edge of what we know.
Physics is the branch of science that studies matter, energy, motion, and the fundamental forces that govern how they interact. The word comes from the Greek physika, meaning "natural things" — and that's a fair description of its scope. Physics asks the most basic questions about the universe: What is matter made of? Why do things fall? What is light? How does energy move from one place to another? Every other physical science — chemistry, astronomy, geology, engineering — ultimately rests on principles physics first worked out.
What makes physics distinct is its method: it doesn't just describe what happens, it tries to explain why in terms of precise, testable, mathematical laws. A biologist might describe how a bird's wing is shaped; a physicist explains the forces of lift and drag that make flight possible at all, in laws that apply just as well to aircraft, insects, or spacecraft.
Physics is usually divided into major branches, each focused on a different scale or type of phenomenon. Together, they cover everything from the smallest particles to the entire universe.
| Branch | What It Studies | Everyday Example |
|---|---|---|
| Mechanics | Motion, forces, and energy of objects | A ball rolling down a ramp |
| Thermodynamics | Heat, temperature, and energy transfer | Why ice melts in warm water |
| Electromagnetism | Electricity, magnetism, and light | How a phone charger works |
| Optics | The behaviour of light | Why a straw looks bent in water |
| Nuclear & Particle Physics | The structure of atoms and their nuclei | How nuclear power plants generate energy |
| Modern Physics | Relativity and quantum mechanics — extremely fast or extremely small systems | How GPS satellites correct for time differences |
Most of the physics taught at school level — motion, force, energy, heat, light, sound, electricity — falls under classical physics, developed mainly between the 1600s and late 1800s. Modern physics, covering relativity and quantum mechanics, emerged in the early 1900s once scientists began studying things classical physics couldn't fully explain, like the behaviour of light or the structure of atoms.
Biology, chemistry, and physics are often taught side by side, but each asks a different kind of question about the same natural world.
| Science | Core Question | Typical Focus |
|---|---|---|
| Physics | How does matter and energy behave, and why? | Forces, motion, energy, matter at its most fundamental level |
| Chemistry | How do substances combine and react? | Elements, compounds, and chemical reactions |
| Biology | How do living things function and survive? | Cells, organisms, and life processes |
These aren't separate worlds — chemistry is really physics applied to atoms and molecules, and biology relies on both. When a chemist studies why two elements bond, they are ultimately describing electromagnetic forces between atoms, a subject physics defined first. This is part of why physics is often called the most fundamental of the sciences.
Few subjects span a range as enormous as physics. The same discipline that explains the behaviour of a particle smaller than an atom also explains the motion of galaxies billions of light-years away.
Physics operates across every scale of the universe — the same fundamental laws that govern subatomic particles also govern the motion of entire galaxies.
Different branches of physics specialise in different parts of this scale. Quantum mechanics handles the strange, probability-based behaviour of particles at the atomic and subatomic level, where the ordinary rules of motion start to break down. Classical mechanics works extremely well at the "human" scale — everyday objects like cars, balls, and buildings. General relativity takes over at the largest scales, describing how gravity shapes planets, stars, and the structure of the universe itself.
Physics isn't confined to laboratories — it's working quietly behind almost every piece of technology in daily life, even when it isn't obvious.
| Everyday Technology | Physics Principle at Work |
|---|---|
| Microwave oven | Electromagnetic waves exciting water molecules |
| Bicycle brakes | Friction converting motion into heat |
| Smartphone touchscreen | Electrical charge and capacitance |
| Aeroplane flight | Lift, drag, and Newton's laws of motion |
| Eyeglasses | Refraction of light through curved lenses |
| GPS navigation | Relativity — correcting for time differences between satellites and Earth |
GPS satellites orbit Earth at roughly 14,000 km/h and experience slightly weaker gravity than we do at ground level. Both effects change how fast time passes for them, according to Einstein's relativity. If engineers didn't correct for this every day, GPS location errors would build up by several kilometres within about a day — physics isn't optional here, it's the reason your map app actually works.
Physics as we know it today was built up gradually, through centuries of observation, experiment, and revision — each major figure building on, and sometimes overturning, the work before them.
A brief timeline of physics: from Galileo's first telescopic observations to Einstein's theories of relativity and the birth of quantum mechanics.
Galileo Galilei, from around 1609–1610, was among the first to use a telescope to systematically study the sky, providing evidence that the Earth was not the fixed centre of the universe. Isaac Newton published his Principia Mathematica in 1687, laying out his three laws of motion and the law of universal gravitation — for over two centuries, this remained the foundation of physics. James Clerk Maxwell, in the 1860s, unified electricity, magnetism, and light into a single set of equations, showing that light itself is an electromagnetic wave. Then in the early 20th century, Albert Einstein published his theory of special relativity in 1905 and general relativity in 1915, redefining space, time, and gravity — while, around the same period, physicists including Max Planck, Niels Bohr, and Erwin Schrödinger developed quantum mechanics to explain the strange behaviour of particles at the atomic scale.
Every time a smartphone locates you on a map, it relies on both Newton's and Einstein's physics working together: Newtonian mechanics predicts the satellite's orbit, while Einstein's relativity corrects for the tiny but crucial time differences caused by the satellite's speed and weaker gravity. Two physics theories, built centuries apart, cooperating quietly in your pocket.
Physics begins with the simplest possible questions — why does this fall, why does that glow, why does the other thing move the way it does — and follows them, patiently and mathematically, as far as they lead. Sometimes that's to a bicycle brake pad. Sometimes it's to the edge of a black hole. Every other branch of physics explored on this site — motion, force, energy, light, sound, electricity, and beyond — builds directly on the foundations laid out here.
12 questions. Select an answer for each, then submit to see your score instantly.