There re three main types of waves. These types of waves are grouped according to how they travel, or WAVE MOTION.

TYPES OF WAVES:

1. Mechanical wawves. Mechanical waves need a material medium to travel (ropes, water, or air are examples). These waves are divided into three different types:
   • Transvers waves - these waves cause the material to move perpedicular to the direction of wave travel.
   • Longitudinal waves - these waves cause the material to move parallel to the direction of wave travel.
   • Surface waves - these waves are both transverse and longitudinal waves mixed in one medium.
2. Electromagnetic waves. Electromagnetic waves do not require a medium to travel. Examples of this type of wae include light and radio waves.
3. Matter waves are produced by electrons. (This is relatively deep physics, and will not be given much attention in this unit. Sorry!)

Most of the information we collect through our senses travels in the form of a wave. Sound travels to our ears in a longitudinal wave. Light travels to our eyes in an electromagnetic wave. Signals that reach our televisions and radios travel in the form of electromagnetic waves, and are converted into picture or sound once reaching the device.

So how do waves move? Waves transfer energy from a vibrating source through whatever medium it is in. For example, if you drop a pebble into a pond, you’ll make a wave that moves out from the center in an expanding circle. The water DOES NOT move. It is the disturbance that moves. After the disturbance passes, the water is exactly where it was before the wave passed. When someone speaks to you from across the room, the sound wave travels through the air as a disturbance in wave form. The air molecules themselves do not move. If the air molecules themselves moved, we would call that wind.

Mechanical waves require a medium. What is a medium? Examples include air, water ropes, a string, etc. A medium is any substance that has molecules and can transfer energy in the form of a wave. Does the type of medium have any effect on wave travel? Of course! Sound travels differently through air than it does through water. In fact, sound travels through cold air differently than it travels through hot air. A wave is just a transfer of energy from molecule to molecule, and so on and so on, until there is no more medium to transmit the wave. That energy is then reflected backward. Think of an echo - once the sound wave reaches solid ground, it can be reflected back toward its source. How well energy is reflected depends upon the density of the medium that is transferring the energy.

How fast waves travel depend upon the medium that the wave has to travel in. Sound waves move at speeds between 330 m/s and 350 m/s in air, depending upon the temperature of the air. Sound moves four times faster in water. Whatever the medium, the speed, frequency, and wavelength of a wave are related to each other, and that relationship is described by the following equation:

Wave speed (γ) = frequency (ƒ) x wavelength (λ)

This relationship holds true for all types of waves.

All mechanical waves require a medium of some sort to transfer energy. Mechanical waves are divided into three types: transverse, longitudinal, and surface.

Transverse waves cause the material to move perpendicular to the direction of wave travel. Click on the diagram with the green dots. The wave will travel to the right, and so you need to make the green dots (or molecules) move up and down. (This should create right angles, for you geometry lovers out there!) Stringed instruments and waves upon the surface of liquids are transverse, as are the electromagnetic waves of light and radio.

Longitudinal waves cause the material to move parallel to the direction of wave travel. If the wave is moving to the right, you need to make the green molecules move left and right (the same direction as the wave travel).

Both of these types of waves transfer energy. Surface waves are a combination of transverse and longitudinal waves. This means that the wave needs to move left and right as well as up and down. Can you make the diagram create a surface wave?

There are two types of waves that you should know about. Let's look at how these work, and remember, it's all about DIRECTION of travel.

Suppose you wanted to create a wave using a jumping rope. Let's say the jumping rope is held stationary (so it doesn't move) by your friend. You shake the free end up and down. The rope moves at right angles to the direction the wave is moving. This is called a transverse wave. Whenever the motion of the medium (the rope) is at right angles to the direction in which a wave travels, the wave is transverse. (To me, the rope looks like a sidewinder snake!)

Waves in musical instruments when the strings are stretched are transverse waves. Which instruments do you know of that generate transverse waves? Waves that travel on the surface or liquids are also transverse. Light waves are transverse, as well as radio waves.

Not all waves are transverse, because sometimes the medium will move back and forth in the SAME direction that the wave travels. The particles or molecules more along the direction of the wave, instead of at right angles to it. Using the example above, you could create this type of wave by moving the rope left and right. The rope would move left and right. This type of wave is called a longitudinal wave.

Are you having trouble telling the difference between transverse and longitudinal waves? You can use a Slinky to create each type. Secure the Slinky on one end to a wall or something else that will not let it move. Then generate a transverse wave by shaking the end of the Slinky up and down. For a longitudinal wave, shake the end of the Slinky in and out. The medium vibrates parallel to the direction of energy transfer. Sound waves are longitudinal, and they are so cool they have their own activity section!