Transverse waves

1. In a transverse wave, the oscillations are at right angles, or perpendicular, to the direction in which the wave travels and transfers energy.
2. If a transverse wave moves from left to right along a rope, each piece of rope moves up and down.
3. The points displaced furthest one way form the crests, and the points displaced furthest the other way form the troughs.
4. A transverse wave is drawn as a smooth up-and-down curve, with the wavelength measured from one crest to the next.
5. Examples of transverse waves include waves on a stretched string or rope, ripples on the surface of water and electromagnetic waves such as light.
6. A guitar string shows the idea clearly, because the string vibrates sideways while the wave travels along its length.

Longitudinal waves

1. In a longitudinal wave, the oscillations are parallel to the direction in which the wave travels and transfers energy.
2. The particles move backwards and forwards along the same line that the wave is moving along.
3. As the particles move, they bunch up in some places and spread out in others, forming a repeating pattern of compressions and rarefactions.
4. In a compression the particles are close together, so the pressure and density there are higher than normal.
5. In a rarefaction the particles are further apart, so the pressure and density there are lower than normal.
6. The compressions and rarefactions travel along, but each particle only moves a short distance back and forth about its rest position.
7. Sound waves are longitudinal, whether they travel through air, water or a solid.
8. The wavelength of a longitudinal wave is the distance from the centre of one compression to the centre of the next compression.
9. The amplitude of a longitudinal wave is the greatest distance a particle moves from its rest position along the direction of travel.
10. A graph of pressure against distance for a sound wave looks like a transverse wave, with peaks at the compressions, but this is only a way of plotting the data and not a picture of how the particles move.

Comparing the two types

1. The two types of wave are told apart by comparing the direction of oscillation with the direction of energy transfer.
2. In a transverse wave these two directions are perpendicular, while in a longitudinal wave they are parallel.
3. Transverse waves are described using crests and troughs, while longitudinal waves are described using compressions and rarefactions.
4. Both types transfer energy from place to place without carrying the material of the medium along with them.
5. Both types are described using the same quantities, amplitude, wavelength, frequency and period, and both obey $v=f\lambda$.