Waves

Everyone is familiar with waves of one form or another, yet how many of us really understand how they are formed and how they behave?

On a safe beach, without any nasty hidden currents it is possible to swim out beyond the breakers and observe wave behaviour close-up. However, if you are a chicken like me, you can sit on the beach and watch the surfers instead.

When a surfer is waiting for a suitable wave, notice how he/she bobs up and down with the waves. The waves do not drag the surfer along with them - they go past, and the surfer just rises and falls with each passing wave.

This is counter-intuitive, like lots of things in physics. What you are observing is that the medium (in this case the water) moves vertically, whilst the wave moves horizontally. So, what is actually travelling in a horizontal direction if the water merely moves up and down? The answer, of course, is energy. Just look at the wear and tear on the cliffs and you can see how much energy is moving!

Even more counter-intuitive, however, are waves that don't seem to move at all. The picture on the left is of bilge water in a boat on the Amazon. What caused such a strange pattern?

Iquitos, Peru, 11/05/2008