Kinds of Energy

You can't hold energy in your hand, or keep it in a jar. So how do we spot it? The trick is to watch for what it is doing. Whenever something is glowing, warming, banging, whizzing, or working, energy is busy nearby — and each way it shows itself has a name.

Play the game "spot the energy" and the world lights up. Here are the kinds you meet every single day:

Light energy — the kind you can see (the Sun, a lamp, a candle flame).
Heat energy — the kind you can feel warming things up (a radiator, a fire, a mug of cocoa).
Sound energy — the kind you can hear (a drum, a shout, a barking dog).
Movement energy — the kind that makes things go (a rolling ball, a running child, the wind).
Electrical energy — the kind that flows in wires to work our gadgets.

Grown-ups sometimes call heat energy thermal energy, and movement energy kinetic energy — long words for the very same everyday things.

Light and heat: two different things

Look at the Sun, a torch, a telly, a firefly — all pouring out light, the energy your eyes drink in so you can see. In a completely dark room there is no light energy at all, which is exactly why you bump into the furniture.

Now hold your hands near a radiator, a campfire, or a mug of hot chocolate. You feel heat energy spreading out and warming you — even with your eyes shut. Heat travels from the warm thing to the cooler thing (that's why the cocoa slowly goes cold and your hands go toasty). Light and heat feel like cousins, but they are not the same: a glow-stick makes light with almost no heat, and a radiator makes heat with almost no light.

Sound and movement: energy you can hear and chase

Bang a drum, pluck a string, clap your hands — the air wobbles and your ears catch it as sound energy. Sound always begins with something shaking to and fro, too fast to see. No shaking, no sound.

And anything that is moving carries movement energy — a football flying into the net, a swing swooping down, a river rushing, you sprinting across the playground. The faster and heavier a thing moves, the more movement energy it is carrying. A gentle rolling marble has a little; a galloping horse has a lot.

Electrical energy — and energy kept in a cupboard

Electrical energy zips along wires to bring the rest to life: it lights the lamp, warms the toaster, spins the fan and sings through the speaker. Almost every gadget in your home is waiting for electrical energy to arrive.

But some energy just sits quietly, stored up and ready, doing nothing yet. There is energy tucked away inside the food you eat, the fuel (like petrol or wood) we burn, and the batteries in a torch or a toy. This parcelled-up, waiting kind is called stored (or chemical) energy — a full battery is like a cupboard packed with energy, ready to be let out the moment you flick the switch.

Watch a firework and you can spot nearly the whole set in a single second. Before it goes up, all its energy is stored quietly inside the powder — a cupboard packed and waiting. Light the fuse and, bang, it all bursts out together: a brilliant flash of light, a loud crack of sound, a wave of heat, and the sparks flung flying in every direction as movement.

One little parcel of stored energy, one instant, and out spill light, sound, heat and movement all at once. Nothing was lost — the quiet stored energy simply changed its costume into four kinds you can see, hear and feel.

One thing, several kinds at once

Here's the surprise that catches most people out: one thing often gives out several kinds of energy at the same time. Switch on a lamp and it makes light — but touch it after a while and you'll feel heat too. Turn on the telly and out comes light from the picture and sound from the speaker together. One gadget, two or three kinds of energy pouring out.

Choose a thing below and watch which kinds light up. Notice how the electrical label glows for the mains-powered gadgets, and how most things give out more than one kind at the same time.

The big idea: energy changes its costume

Energy loves to swap from one kind into another — that is really its whole job. Follow the energy through a torch: it starts as stored energy in the battery, turns into electrical energy flowing up the wire, and comes out of the bulb as light (with a little heat — feel the bulb!). Stored, then electrical, then light — the very same energy, wearing three costumes one after another.

You do it too. Bang a drum and your arm's movement energy becomes sound energy. Eat your breakfast and the stored energy in the food becomes the movement energy of you racing round the garden. Once you start looking, you'll catch energy changing costume everywhere.

If energy can turn into electrical energy, could we make our own? Yes! On a windy hill stand giant white wind turbines. The wind's movement energy pushes their huge blades round, spins a machine inside, and out comes electrical energy that flows down the wires to homes and schools.

You can do the same on a bike. Some bicycles have a little dynamo pressed against the wheel. As you pedal, the wheel's movement spins the dynamo and makes just enough electrical energy to light your lamp. Stop pedalling and the lamp fades — no movement, no electricity. Your legs are the power station.

Energy is never made out of nothing, and never destroyed. It only changes from one kind into another. When a torch battery "runs out", the energy didn't vanish — it all left as light and heat.
Heat and light are different kinds of energy. Something can glow without being hot (a glow-stick) or be hot without glowing (a radiator). Don't muddle them up.
"Electrical energy" is not the tiny bits flowing in the wire. The wire carries a flow (grown-ups call it electric charge), but the useful energy it delivers is what turns into light, heat, sound and movement at the other end.