By Sam Baron

What is energy made of? – Ela, 8, Melbourne

Hi Ela! What a great question!

For scientists, energy is not really one thing and therefore it is not made of anything else, like a house is made of bricks.

Energy is more like a capacity. An ability is an ability to do something.

Energy and work
Think of a musician: he has the ability to play an instrument. A painter has the ability to paint.

Energy is the capacity for something to do work.

Something works when it exerts a force on another object, causing the object to move in a particular direction.

What does it mean? Well imagine someone throwing a ball at you and you hit it with a bat. When the bat hits the ball, it changes the speed and direction of the ball.

Energy is the bat’s ability to change the direction of the ball. When the bat swings, it can change the direction of any ball it hits.

When you swing the bat, you put energy stored in your muscles into it. The harder you hit, the more work the bat can do, so the more energy it carries.

Energy types
There are many ways for something to work, so there are different types of energy.

We have already encountered one: the swing of the bat. This is called kinetic energy. It is the energy that something has because it moves.

Another type of energy is potential energy. Potential energy is the ability of something to function because of its position in relation to other objects.

This means that putting things in certain places gives them energy.

Here’s a fun example: imagine putting a bucket of water on a half-open door. When someone walks through the door, the bucket falls on their head.

Because the bucket is over the door, it can fall. And when he falls he can do some work. Not only will it soak anyone who walks through the door, but it will also hit them on the head.

Thus, the bucket has the ability to work just because it is placed over the door, and not because it is in motion. This capacity is the potential energy of the bucket.

Einstein’s famous equation The famous physicist Albert Einstein made an energy equation, which you may have already seen: E = mcÂ².

In this equation, the E is for energy, the m is for mass (which is roughly the amount of matter, or physical substance, in something), and c means the speed of light.

What the equation seems to say is that energy is equal to mass times a number. So isn’t energy made of something after all?

Not quite, because some massless things can still have energy. For example, light. We know it has energy because we capture the energy from light in solar panels and turn it into electricity.

But light is made up of tiny particles called photons, and photons don’t have mass.

So if energy was made up of mass, then light would have no energy at all! It would make solar energy a mystery.

It turns out that even though light has no mass, it has what’s called momentum, which gives it the ability to do work.

Mass, energy and momentum
There is a more complicated version of Einstein’s equation that shows how energy relates to mass and momentum.

An important thing to know is that light travels very quickly. Because the amount of energy in something depends on the mass it has multiplied by the square of the speed of light, that means a little bit of matter carries a lot of energy!

Light travels nearly 300 million meters in a single second, which means that one kilogram of mass equals nearly nine quintillion joules of energy! It’s a 9 with 18 zeros after: 9,000,000,000,000,000,000.

The trick is to unleash this ability. This is actually how nuclear bombs (and nuclear power) work: they release the energy captured in matter to produce a huge effect. 