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molecules and splattered against the wall, however, because the molecules pass on their energy in
a domino effect. It’s the same as using a ‘slinky coil’. The energy goes in one end, moves all of the coils back and forth, and comes out at the other end. In air the sound source compresses the molecules next to it, which then compress the ones next to them and so on until it reaches the listener.
A wave doesn’t compress the molecules very much as it travels, but it does cause a change in the pressure on the ear. The loudest sound you can tolerate adds about
0.05kg per sq m of pressure. But since the pressure on your inner ear is balanced for still air, the extra pressure of the wave causes the eardrum to be pushed very slightly each time the wave arrives. Once the wave has passed, the eardrum springs back and is then pushed in by the next wave. In this way the waves make the eardrum vibrate and pass a message to the inner ear.
Sound waves behave like light waves in many ways. Sound waves can, for example, be reflected, or bounced, from objects, just like light waves. (See also: Decay and Frequency.)
Speed of light
Beam of white light
Red Orange Yellow Green Blue Indigo Violet
 Spectrum – When light is refracted through a prism, the colours of the spectrum are produced.
longer lengths, then orange, yellow, green, cyan and blue. Violet colours are produced by the shortest waves.
Sound: The range of sound waves that we can hear, normally from 20Hz to 20kHz.
Speed of light
Light does not travel instantly from one place to another. It takes time for the light waves to get from
their source to their destination. However, light travels so fast (about 300,000 kilometres per second) that we do not notice this delay when we turn on a light. It is only noticeable over long distances.
Astronomers know that it takes light a long time to reach us from other parts of the universe. They use this knowledge to measure distances in light-years. The furthest objects we can detect are billions of light- years away from us. The light we see from them now was generated billions of years ago. In this way
we are seeing what the universe was like billions of years ago.
We have no idea what it is like today because light produced from these vast distances away will not reach us until billions of years
in the future. (See also: Index of refraction.)
 Spectrum – The spectrum can be seen in a rainbow.
Speaker
(See: Loudspeaker.)
Spectacles
(See: Eyeglasses.)
Spectrum
A range of frequencies.
Light: The range of light waves
that our eyes can see – separated out. This happens in the sky to produce a rainbow and also in a glass block called a prism. Red colours are made by the waves with
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