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Energy changes form

Energy and power · level 2, lesson 4 of 6

A question to start

You eat breakfast, run up a hill, and slide down the other side on a sledge. Can you follow the energy all the way, from your plate to the bottom of the hill?

The idea

Energy comes in many forms:

Form Example
Kinetic (moving) A rolling ball, the wind
Gravitational (height) A book on a high shelf
Elastic (stretched) A pulled-back bow
Chemical (in substances) Food, batteries, fuel
Thermal (heat) A hot cup of cocoa
Light Sunshine, a lamp
Sound A drum, a voice
Electrical Electricity in a wire

Energy can change from one form into another. Almost everything that happens is energy changing form.

chemical(food)moving(running up)height(at the top)moving(sliding)

When energy changes form, some always turns into heat along the way. Your muscles get warm when you run. The sledge's runners warm the snow a little as they rub.

On Mars, the energy chain of a solar-powered rover goes: light from the Sun → electrical energy from the panels → chemical energy stored in the battery → electrical energy again → kinetic energy as the wheels turn, and some heat.

Worked examples

1. A torch. Chemical (battery) → electrical (wire) → light, and some heat (the bulb gets warm).

2. A wind turbine. Kinetic (wind) → kinetic (spinning blades) → electrical.

3. A firework. Chemical → light, sound, heat and kinetic.

Try it

  1. What form of energy is stored in food?
  2. What energy change happens in a solar panel?
  3. Follow the energy in a toy car with a battery.
  4. Why do your hands get warm when you clap?
Answers
  1. Chemical energy.
  2. Light → electrical.
  3. Chemical (battery) → electrical → kinetic (moving), and some heat and sound.
  4. Some of the moving energy of your hands turns into heat (and sound) when they hit.

Common mistake

"Energy gets used up and disappears." Energy never disappears. It only changes form, and in the end most of it becomes heat that spreads out into the surroundings.

Where it leads