Have you ever thrown a stone into a pool of water and watched the circular ripples move toward the edges? Maybe you've seen how the wind makes the ears of wheat or the waves of the sea ripple on a stormy day. All of these examples are wave patterns. You may not know that light and sound are also wave patterns.
Think of ocean waves. The ocean waves continuously ripple toward the shore, one after the other, day and night. How is it possible for this to happen without flooding the beaches? The reason is that waves do not actually carry water. When a wave travels toward the shore, the water moves up and down, but it does not move forward. Even though it looks like the water is moving forward, only the wave is moving toward the shore.
To better understand, think about this example of waves: What happens to a canoe or a layer of leaves on top of a lake when a motorboat passes nearby? The motorboat produces waves that make the object go up and down. As the waves continue to move forward, the object remains in the same place. Why? The motorboat disturbs the stillness of the water surface. This turbulence moves over the surface of the water in the form of repeated curves or ripples.
You know the meaning of the word disturb. Imagine you are taking a nap in a hammock; suddenly a friend comes along and knocks you to the ground. You could say that your friend disturbed your rest or that your friend is a disturbance. When your friend leaves, you continue your nap. In the same way, particles in the water in a resting position are disturbed by waves. When the turbulence ends, the water particles are at rest, not carried away by the waves.
You have already learned that it cannot be matter. Waves carry no matter, no canoes, no leaves, not even water. The same is true of any kind of wave. What does a wave carry with it? Waves carry energy with them. A wave is a turbulence that carries energy from one place to another.
To understand how waves form, try forming a wave. Tie one end of a rope to a pole. Give the other end a tug until you can observe the "bend" or movement of the wave reaching the other end. Do this motion several times to create a series of waves.
The movement of your hand produced the wave. Any movement that repeatedly follows the same path is called a vibration.
You may already know about vibrations. The surface of a drum vibrates when you hit it with a stick. It moves up and down, creating a special sound. By picking up the sound, the vibrating eardrum allows you to hear. If you touch a taut elastic, it will vibrate for a few seconds. In the same way a guitar string vibrates. Even the Earth can vibrate during a powerful earthquake.
An object that vibrates is moving. An object that is moving has energy. An object transmits some of its energy to the particles around it and makes them vibrate. These, in turn, pass the energy to the nearest particles, and so on. Waves, whether waves, waves on a string, sound waves or microwaves, are produced by vibration.
The motorboat gave energy to the water particles in the lake. You gave energy to the rope by moving it by hand. The wind blowing on the lake produces the waves. Electric charges, like the ones you see and feel when you receive an electric shock, can create light and microwaves. A sound wave is produced when air is energized by the vibration of a guitar string.
