Page 191 - Physics Coursebook 2015 (A level)

Chapter 13: Waves
Vibrations making waves
The wind blowing across the surface of the sea produces waves. The surface of the water starts to move up and down, and these vibrations spread outwards – big waves may travel thousands of kilometres across the ocean before they break on a beach (Figure 13.1).
Figure 13.1 This photograph shows a wave breaking on the shore and dissipating the energy it has drawn from the wind in its journey across the ocean. The two scientists are ‘storm chasers’ who are recording the waves produced by a hurricane in the Gulf of Mexico.
Describing waves
When you pluck the string of a guitar, it vibrates. The vibrations create a wave in the air which we call sound. In fact, all vibrations produce waves of one type or another (Figure 13.2). Waves that move through a material (or a vacuum) are called progressive waves. A progressive wave transfers energy from one position to another.
At the seaside, a wave is what we see on the surface of the sea. The water moves around and a wave travels across the surface. In physics, we extend the idea of a wave to describe many other phenomena, including light, sound, etc. We do this by imagining an idealised wave, as shown in Figure 13.3 – you will never see such a perfect wave on the sea!
wavelength, λ
0
displacement, x
Figure 13.2 Radio telescopes detect radio waves from distant stars and galaxies; a rainbow is an effect caused by the reflection and refraction of light waves by water droplets in the atmosphere.
wave
amplitude, A
line of undisturbed positions
Distance
Figure 13.3 A displacement– distance graph illustrating the terms displacement, amplitude and wavelength.
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Displacement