- Establish that sound needs a medium to travel through. Show pupils an electric bell ringing inside a bell jar. Ask them to predict what will happen if the air is pumped out of the jar, and test their predictions. If the pump is noisy, it would be better to listen as air is let back in.
- Ask pupils whether sound travels through solids,
eg Can you hear through closed doors? Can animals hear under water? Ask pupils to carry out some quick activities to demonstrate transmission of sound through solids and liquids,
eg battery-operated radio in sealed plastic bag under water using a hydrophone, sound passing through a wooden bench, a length of metal rod, a string telephone. Help pupils to make comparisons with sounds from the same source transmitted through air and establish that transmission is more effective through denser media. Ask pupils why this may be so, reminding them of the particle model of solids, liquids and gases. Help pupils to record what they found out,
eg using annotated diagrams.
- Remind pupils that sound travels much more slowly than light,
eg fireworks. Ask them if sound travels at different speeds in solids/liquids/gases. Draw on experiences,
eg singing railway lines before the train is heard through air, listening closely with an ear to a metal railing that is tapped some metres away. Ask how they might measure these differences. Quote the example of the two people who, some 100 years ago on Lake Geneva, measured the speed of sound in water. One made a visual signal while striking a bell under water. The other started his stopwatch and plunged his head in the lake until he heard the bell.
- Encourage pupils to explain the differences using the particle model.
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- state that sound cannot travel through a vacuum but can travel through solids, liquids and gases
- describe how sounds travel through solids, liquids and gases
- explain in terms of the particle model why sound needs a medium
- explain how sound travels at different speeds in different types of material
- explain everyday phenomena in terms of the different speeds at which sound travels in air and solids
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