# Waves

#### Box # 1: What are Waves?

What is the first thing that comes to mind when you think of a wave? Maybe an ocean wave from the hot days of summer you have spent over in Fire Island? Perhaps you might be thinking of “the wave” from a baseball game? They are both examples of waves. A wave is a form of energy. Light, heat and sound travel as waves. Most waves travel through some type of matter. This matter the wave travels through is called the medium. The medium of an ocean wave is the water. The medium of “the stadium wave” would be the people. When a wave travels through matter, its size or shape do not change, only the arrangement. Think about this: When you are doing “the stadium wave” you arms/body go up and down. You never lose or gain weight as the wave passes through you.

The wave you might be most familiar with is transverse wave, such as an ocean wave. A transverse wave moves the medium at right angles to the direction of the waves energy. This simply means the matter moves up and down while the energy moves side to side.

The other type of wave is a longitudinal wave. Have you ever made a long chain of dominoes? You might have knocked one over and the rest fell down, one right after the other. This is an example of a longitudinal wave. A longitudinal wave moves the medium in the same direction as the energy of the wave. In other words, the energy and the matter move side to side.

#### Box #2: “Bill Nye” Movie

The following facts are taken from the Bill Nye movie:
Energy moves as waves.
Waves have two basic shapes. The sizes of these waves are different.
Quiet sounds have less energy than loud sounds.
Sound waves move through water at 1,500 (5,000 feet) meters per second.
Light waves are the fastest waves we know of in the universe. They move 300,000 kilometers per second.
Waves with high amplitudes carry large amounts of energy.

#### Box #3: Parts of a Wave.

Parts of the transverse wave:
Crest = The highest point of the wave
Trough = The lowest point of the wave
Wavelength = The distance between two identical points of the same wave. Measured from crest to crest or trough to trough.
Rest = Baseline. No energy.
Amplitude = The height of the wave. Measured from rest to crest.

Parts of the longitudinal wave:
Compression = Area where the particles are pressed together.
Rarefaction = Area where the particles are spread apart.

#### Box #4:Wave Properties

When watching an ocean wave come into shore you may notice that the wave changes as it approaches. Waves will change size, speed, height and length. Wave amplitude is a good measure of how much energy that wave contains. Think about this… When you are at the ocean which wave is going to knock you over with the greatest force: a 3-foot wave or a 12-foot wave. Of course the 12-foot wave is going to knock you over. The higher the wave the more energy it is going to carry.
When you decide how to enter the ocean you look at the waves and try to figure out how often the waves are breaking onto shore. With out even knowing it you are calculating wave frequency. The frequency of a wave is calculated by how many waves pass a point in one second. The unit used to measure frequency is called hertz.
How fast a wave is move is called the wave speed. the formula for wave speed is:

speed = frequency x wavelength

#### Box #5: Reflection

Have you ever heard an echo? Most likely you see yourself in the mirror in the morning. These are both examples of wave reflection. Reflection is the bouncing back of a wave. When wave hit a barrier directly they will bounce back in a certain direction. We can predict this direction by using the Law of Reflection. The Law of Reflection states that the angle of incidence equals the angle of reflection. If you play pool you might have used this law to take a shot off of the bumper.

#### Box #6

Box #6 Diffraction
Try to think back to when you were a little kid playing outside on a summer day. It’s now time to come in for dinner and you can hear your mom calling you, but you cannot see her. The waves are traveling around a barrier. The bending of waves around a barrier is called diffraction.

#### Box #7: Refraction

The sound waves are traveling to you by the way of refraction. Waves changing speed and direction as they travel through different mediums is called refraction.

#### Try This…

Materials:
1 clear drinking glass
1 pencil
Fill the glass half way with water. Place the glass on the table or counter top. Next, place the pencil in the glass. Take a few steps away from the table. Look at the glass from the side. Does the pencil look broken?
This is happening because of refraction. The light waves are going through two different mediums (i.e. water and air). The light waves change direction and speed as they go from the air into the water. Therefore the pencil appears to be broken.
Materials:
1 glass filled half way with water
1 coffee mug
1 penny
Place the penny in the bottom of the coffee mug. Stand over the mug so that you can see the penny. Slowly move back until you can just see the very edge of the penny. Now have someone else carefully fill the coffee mug with water. What do you see?
You should have a better view of the penny. It appeared as if the penny moved. What really happened was the light waves were bent when they entered the water. Thus allowing you to see the penny.

#### Box #8: Wave Interference

Think to a time when you have been on a boat. A boat leaves a trail of waves behind as it travels through the water. When two boat pass each other there waves interfere with one another. Two or more waves coming in contact with one another is called interference. There are two type of interference: constructive and destructive. Constructive interference produces a wave with a larger amplitude. Destructive interference produces a wave with a smaller amplitude.

Below is a link that will show you what happens when two waves come in contact with one another.

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