100 Physics Ideas in 100 Words

g CONTENTS

Energy

We can think of a lump of coal as a store of energy: burn it with oxygen and it can keep us warm; burn it in a steam engine and it can move a train on rails. And yet when we look at a piece of coal it seems to be an inert, black mass. It may have been buried underground for 360 million years. Where is the energy that is released by burning?

The word “energy” comes from the Greek word energeia, meaning “activity”, and yet there is no evident activity in a lump of coal. Rather, coal stores energy that is the result of activity in the past – photosynthesis by trees millions of years ago.

Isaac Newton didn’t think in terms of energy – the scientific idea had not been developed in his day. Today, rather than thinking of energy ...