Just What is Physics?

Just What is Physics?

If you study IGCSE Physics, you will learn about a number of topics – mechanics, electricity, waves, magnetism, and so on. Traditionally, these topics were summed up in the phrase ‘heat, light and sound’. To many students, this may seem like a strange rag-bag of topics. What unites them? Why do they all belong under the heading of ‘Physics’?

It’s not difficult to see why these topics don’t belong in Biology – there are no living organisms involved (although a physicist might claim that you can understand a lot about plants and animals if you apply Physics principles to them). Nor is Physics concerned with chemical reactions, so it is different from Chemistry.

Once you move on to studying Physics at A Level, the unity of Physics becomes more obvious. Here is what a physicist sees when looking out of the window. A car is travelling along the road. It is a cuboid mass, acted on by four forces. A second mass approaches and they collide. New forces appear and disappear, transferring momentum between the two masses. Where once there was kinetic energy there now is thermal energy.

By picturing the forces we can explain how the cars interact. By calculating the energy changes, we can deduce how warm the environment will become. We could help the police as they try to determine who was responsible.

The point is that physicists have a very abstract view of the world. Look through any Physics textbook and you will see numerous diagrams in which objects are represented by circles and rectangles. Arrows represent forces and movement. Plus and minus signs indicate electric charge. Wavy lines represent radiation.

Biologists have to worry about millions of living species. Chemists have 100 elements and their billions of possible compounds. To a physicist, the Universe can be reduced to one simple idea: there is nothing but particles and the interactions (forces) between them. Ultimately, that is all there is. By understanding how particles interact, we can explain many, many different phenomena, including ‘heat, light and sound’.

This is why Physics is often described as ‘reductionist’. It seeks to explain complex phenomena using a very few fundamental ideas. The development of quantum theory in the twentieth century showed that these fundamental ideas are not exactly common sense. Particles at the atomic level behave very differently from cars moving along the road. However, quantum ideas are not so difficult that students can’t begin to make sense of them at A Level and, with a good teacher, that can give students a glimpse of the exciting ideas which are covered in an undergraduate Physics course.


David Sang is an experienced author, teacher and researcher. He is author of Cambridge IGCSE Physics and Cambridge International AS and A Level Physics.

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