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What is Energy?

What is Energy? My Dad said “the ability to do work” but then told me that was a rubbish answer!
Matthew Cosgrove from Greater Manchester (age 5-14)

What is matter? Alternatively – what is energy? The answer “the ability to do work” is not sufficient
Andrew McDonald from Stirling (age 45-54)


2 Responses

  1. Your dad’s answer is actually quite good. First you’ve got to eat a tasty chocolate bar, which is then a bit annoyingly stored as fat in your body. Then when you one day want to walk up a hill your body uses the fat to move the muscles. So here food is transformed into fat and then into the ability to walk up a hill. But you can only do so and so much from certain amount of food you ate. Say, if you wanted to climb a really high hill, you need more than just one chocolate bar. To keep track of how much you can do, you assign a certain amount of energy to the chocolate bar; this tells you how much fat you get from it, so the fat has the same energy, and finally that energy tells you how high a hill you can climb up.

    So physicists use energy as a book keeping tool to avoid loosing anything when things are transformed from one state into another (like chocolate into you standing on a hill) and it also helps to tell how much of the other thing you can get (the height of the hill you can move up from a single chocolate bar).

    Imagine you had a big pile of lego blocks. From these you can build a few objects and you can take one object apart again to build another one, or take two objects and build one new one from it, and so on… lots of possibilities, but you can only use the amount of lego blocks in the objects, not more, but also not less (if you don’t use them they are left over on their own, but they are still there). So if you count the lego blocks and know how many lego blocks you need for the objects, you can tell exactly what you can build and what not. Counting lego blocks is a bit like energy, just that it’s not only about different objects, but also doing things, etc.

    Now the universe is not build from lego blocks, but from some really weird things. We can give each of these things a certain amount of energy, which tells us a bit what they are and what we can do with them (like building things from lego blocks of various sizes). Describing them with energy is really useful – but it’s more to have an idea of what is going on (to build a model of the real world). We don’t really know what these things are – they aren’t particles, nor waves, but a bit of both and we still try to understand this better.

  2. Thanks for your answer it has helped us understand physics a bit more.

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