Waves

A wave is a disturbance that travels through space and transports energy. In the ocean, waves
are created by energy moving through the water molecules. The water molecules themselves stay put - it is the energy that moves through them that creates the wave motion. The disturbance of one water molecule causes the adjacent water molecule to move as well. As each water molecule bumps into its neighbor, the energy from the disturbance is passed on. Where does this energy come from? When we are talking about ocean waves, the energy typically comes from the wind (however, underwater earthquakes and/or volcanic eruptions can also trigger large ocean waves known as tsunamis) . Explore the following interactive lesson to learn more about waves:

Here's how it works: when the wind blows across the surface of the ocean, friction is generated. Friction transfers energy from the air to the water molecules, the result of which is a wave. The stronger the wind, the larger the wave will become. If the wind is strong enough, waves can travel thousands of miles across the ocean before they reach land. Along this journey to the coast, the waves continue to generate energy and strength. When the wave approaches the shore, it begins to touch bottom. Water drags along the seafloor, which causes the movement of the wave to slow down. This causes water to pile up, building higher and higher waves. Eventually the wave reaches a point where the steep advancing edge collapses, and the waves disintegrate into sheets called swash which carry sand and gravel onto the beach.

The progression of a breaking wave. Courtesy of the National Park Service.

There are many different properties of a wave that can be measured, including the wave height, wave length, and period. The wave is the distance between its trough (the lowest point of a wave) and its crest (the highest point of a wave). The wavelength is the distance between two consecutive wave crests. The wave period is the amount of time that passes between one wave to the next.

The size of the wave that is created is dependent upon three factors: 1) Wind speed. The stronger the wind, the larger the waves formed; 2) The distance the wind travels over the ocean surface (this is called fetch). If wind can blow over long distances it will transfer more energy and therefore create more and bigger waves. 3) How long the wind blows over the water. Longer durations of wind will allow for the transfer of more energy and create more and bigger waves. The following video explains how big waves form off the coast of California.

Sources: Teachers' Domain, Making Big Waves, published August 30, 2007, retrieved on June 16, 2010, http://www.teachersdomain.org/resource/kqed07.sci.ess.bigwave/ and Teachers' Domain, What Is a Wave?, published August 9, 2007, retrieved on June 16, 2010, http://www.teachersdomain.org/resource/lsps07.sci.phys.energy.waves/
Last modified: Tuesday, 31 January 2012, 10:21 AM