5.1 An Introduction to Waves - Longitudinal and Transverse Waves

When you think of a wave, you may not necessarily think of sound waves, or light waves, but instead ocean waves, or even a hand waving. However, even these last two examples are useful in understanding waves. A wave is a periodic disturbance in a medium (or in space). Both the motion of the hand and of the ocean are periodic. The ocean wave is a disturbance of the water, and the hand is a disturbance in space (you could also say that it creates a disturbance in air!).

When considering wave propagation, there are two main kinds of waves, transverse waves, and longitudinal waves. Transverse waves are those in which the wave components (i.e. the individual parts of the medium that is transferring the wave) oscillate in a perpendicular direction to that of the wave motion. Consider a buoy sitting on the surface of the ocean, for example. As a wave goes by, the buoy rises with the crest of the wave, and falls with the trough. It bobs up and down regularly as the waves pass from one side of it to the other, but it doesn’t get carried with the water. The motion of the buoy is in a vertical line, while the water moves horizontally. The crest of a wave is the highest point that it reaches, while the trough of the wave is the lowest point. These are respectively the maximum and minimum amplitudes, or displacement of the wave.