Why are there waves on the sea?

Only very rarely are the seas completely still. These were the times that sailors on the old sailing ships feared the most – even more than they feared the worst storms. They became becalmed, which meant that no wind was blowing to fill the great sails to carry them to their next port of call. The sea would be motionless and mirror-like and no rain would fall. If the sailors were held fast for too long their food would begin to sun out, and perhaps more important fresh water would become scarce.

You may have guessed by now the connection between waves on the sea and the wind. In fact, waves are almost wholly the result of the wind blowing across the surface of the water. Perhaps you have played ‘blow’ water polo at home. You need a table tennis ball, two pieces of tube and a bowl full of water. Float the table tennis ball in the bowl and blow through the tubes. As you blow on to the water you will notice that the surface is stirred up into ripples – the harder you blow the bigger the ripples.

It is very similar on the sea. The wind drags the water to form waves which slowly move forward and get larger. Although the wave shape moves forward, each particle of water moves round in circles and does not change its average position. The height of a wave depends upon three factors. How hard the wind is blowing, how long the wind has been blowing, and the fetch. The word fetch means the length of the stretch of open water over which the wind is blowing.