Waves may be either transverse or longitudinal. • The ripples on a water surface are an example of a transverse wave. • Longitudinal waves show areas of compression and rarefaction. • Sound waves travelling through air are longitudinal. • Students should be able to describe the difference between longitudinal and transverse waves. • Students should be able to describe evidence that, for both ripples on a water surface and sound waves in air, it is the wave and not the water or air itself that travels.