Water
on Earth
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The understanding of waves is the same whether the waves are moving through air, water, a piece of rope, or anything else.
We will start by considering a common experience. Everyone has probably had the experience of making a wave in a piece of rope or string. If the string is firmly attached at one end, you can make a wave by pulling up on the other end. You will produce a "bump" that will travel to the other end of the string.
| Start with a string fixed at one end to a wall. |  |
| Pull up, then down, on the free end of the string. |  |
| You will make a "bump." |  |
| But the bump is not stable. The string had to be stretched to make the bump, so it is under tension. This tension is pulling the crest of the bump down. Also, the point where the bump meets the straight part of the string is under tension, pulling up on the string adjacent to the bump. |  |
| Thus, the crest of the bump falls, and the rising string to its right creates a new crest. Thus, the bump moves away from its origin. |  |
This creates a wave, which moves away from its point of origin.
Waves in water are caused in just the same way. Although water is not solid, like a string, the individual molecules of water are stuck to each other just as the molecules of as string are. After all, if the water molecules were not stuck together the water would not be a liquid but a gas. Thus, any disturbance in a body of water creates a wave, moving away from the point of disturbance.
Notice this about the string: The string does not move from left to right; the individual parts of the string move up and down, but only the wave moves left to right. The same is true for water. A cork placed on water bobs up and down with the waves (perhaps making a slight circular motion) but does not move sideways along the surface.
Well, that depends on the nature of the wall. Suppose the wall were free to move up and down (say, on a track). When the wave gets to the wall it causes the wall to move up and down. Thus, we can say that the energy that you gave to the string has been transferred by the wave. A wave is, in fact, a very efficient way to transfer energy from one place to another: the motion energy of ocean waves, sound energy moving through air, or electromagnetic energy moving with a light wave.
Suppose the wall is rigidly fixed. The energy of the wave is still there. What happens to it? It gets reflected, and the wave starts moving back the other way. Just the same thing happens with ocean waves, sound waves, or light waves.
Waves always have the same shape, unless they are disturbed, That is
true whether the waves are in water, in air, or in space. This shape is
the one shown in the drawings above. Sometimes waves on a body of water
look different, more like this:
This happens because the tops of the waves are blown into this shape by the
wind.
Pictures sometimes show ocean waves this way, but it is better to have
students understand that the shape of an undisturbed wave is this: 
Sometimes the wind is strong enough to cause the tops of the waves to be
disturbed so that you get foam - this gives us whitecaps.
Consider the following picture (1). As the wave moves in to shore, the bottom gets shallower and shallower. Now, it turns out, for waves in water, if the bottom is shallower, the wave moves slower. As the wave approaches the shore, the leading edge of the wave is in shallower water than the trailing edge (2).
(1)
(2)
The top of the wave tumbles forward, eventually breaking over the leading edge.
(3)
In this one limited situation, it is true
that for a short time the water is actually moving forward with the wave;
the water in the crest of the wave is carried forward by its greater speed.