What is energy?
Energy is the ability to make something happen: to move, heat, light up or make a sound. You can’t hold energy in your hand, but you can see what it does. Everything you do uses energy, from running to thinking.
Forms of energy
| Form | What it is | Examples |
|---|---|---|
| Kinetic energy | Energy of motion | A rolling ball, wind, a running dog |
| Potential energy | Stored energy | A stretched rubber band, a book on a high shelf |
| Thermal energy | Heat from moving particles | A hot stove, warm soup |
| Light energy | Energy we can see | The Sun, a lamp |
| Sound energy | Energy from vibrations | Music, a drum |
| Electrical energy | Moving electric charges | Lightning, a plugged-in toaster |
| Chemical energy | Stored in food, fuel and batteries | A sandwich, gasoline |
Kinetic energy
Anything that moves has kinetic energy. The faster it moves and the heavier it is, the more kinetic energy it has. A truck rolling at 50 km/h has much more kinetic energy than a bicycle at the same speed.
Potential energy
Potential energy is energy waiting to be used.
- Gravitational potential energy: things that are high up can fall. A roller coaster at the top of a hill has lots of it.
- Elastic potential energy: stretched or squished things can spring back. A drawn bow or a compressed spring.
- Chemical potential energy: stored in food, fuels and batteries.
Energy transformations
Energy changes from one form to another. This is called an energy transformation.
| Device or event | Energy change |
|---|---|
| Flashlight | Chemical (battery) → electrical → light |
| Toaster | Electrical → thermal |
| Eating and running | Chemical (food) → kinetic |
| Solar panel | Light → electrical |
| Roller coaster | Gravitational potential → kinetic |
| Drum | Kinetic → sound |
| Campfire | Chemical → thermal + light |
The roller coaster
At the top of the first hill, a roller coaster has lots of potential energy and very little kinetic energy. As it zooms down, potential energy changes into kinetic energy, and it speeds up. As it climbs the next hill, kinetic energy turns back into potential energy, and it slows down. That’s why each hill is a bit shorter than the last: some energy changes into heat and sound from friction.
Energy is never lost
Conservation of energy means energy can’t be created or destroyed. It only changes form. When a bouncing ball stops, its energy hasn’t vanished. It has turned into heat and sound.
Where does our energy come from?
Almost all energy on Earth starts with the Sun.
- Plants use sunlight to make food (chemical energy).
- Animals eat plants.
- Fossil fuels like coal and oil formed from ancient plants and animals.
- The Sun heats air, creating wind.
Saving energy
Some energy sources, like coal and oil, will run out and cause pollution. Others, like solar and wind, are renewable. You can save energy by:
- turning off lights when you leave a room
- unplugging chargers
- walking or biking for short trips
- closing doors to keep heat in
Common mistakes
- Thinking energy gets "used up." It changes form, often into heat.
- Thinking only moving things have energy. Still objects can store potential energy.
Try it yourself
- Roll a marble down a ramp from three different heights. Measure how far it travels. What pattern do you see?
- List five devices in your home and the energy transformation each one makes.
- Rub your hands together quickly for 10 seconds. What energy transformation happened?
Quick recap
- Energy is the ability to cause change.
- Kinetic energy is motion; potential energy is stored.
- Other forms include thermal, light, sound, electrical and chemical energy.
- Energy transforms from one form to another.
- Energy is conserved; it changes form but is never destroyed.