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Scientists say that energy is the ability to do work. It comes in many forms, for example heat, light, motion, sound, electrical, chemical and gravitational energy.

Energy is grouped into potential (stored) energy and kinetic (working) energy. Chemical energy in food, batteries and fuels, a stretched spring and an object high up are all stored energy; light, heat, sound, electricity and motion are working energy.

Energy changes from one form to another. A cyclist rolling downhill turns gravitational energy into motion energy. In a hydroelectric dam, falling water turns a turbine that produces electricity.

Experiment: How high does a ball bounce back?

1. Hold the ball next to the metre stick with its bottom at 25 cm. Let it drop: do not throw it.
2. Your partner watches where the bottom of the ball reaches at the top of its first bounce. Write it down.
3. Repeat from 50 cm, 75 cm and 100 cm.
4. Do each height three times and work out the average bounce height.
5. Fair test: use the same ball, the same floor and always just let go.
6. Does the ball ever bounce back to the height you dropped it from? Where did the rest of the energy go?

Drop height (cm)	Bounce 1 (cm)	Bounce 2 (cm)	Bounce 3 (cm)	Average bounce (cm)
25
50
75
100

Questions

1. Draw an energy chain for a torch: battery → … → … Label each form of energy.

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2. Why does a ball never bounce back as high as it was dropped?

3. In your experiment, what did you change, what did you measure and what did you keep the same?

4. Give two reasons why an LED bulb is better than an old incandescent bulb.

Sources for every fact on this sheet: echoesof.science/school/energy/sources/

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