Waves and Energy

Study the video of the mass on the spring again. To start the spring vibrating you must put some energy into the spring. Suppose we wanted to transfer some energy from the spring/mass system to a point one meter to the right of the mass. How would we do it?

One way would be to tie a light string to the mass and the other end to the point where we want the energy. The vibrating spring would cause the string to oscillate and energy would be transferred along the string to where we wanted it.

Let us examine a vibrating string more closely. In the following video clip a light string is attached to a modified audio speaker. A signal generator causes the speaker to vibrate at a known frequency that in turn vibrates the string.

Move the mouse cursor in the video window to play the video.

After studying the video please answer the following questions:

How does the frequency of vibration of the speaker compare to other points on the string?
Suppose we used a red marker to make at dot on the string. Describe the motion of the dot as the string is vibrating.
In what direction is the energy from the speaker being transferred?

We encourage you to setup a vibrating string yourself. If you don't have access to a mechanical string vibrator, simply tie one end of a piece of string so as to hold it stationary and use your hand to vibrate the string.

A vibrating spring is an example of a transverse wave. In this kind of wave the medium (in this case the string) moves perpendicular to the direction of energy transfer.

Study the following video clip of a slinky spring.

Answer the following questions:

In what direction does the medium move?
What is the direction of energy transfer?

A slinky is an example of a longitudinal or compression wave.

Please make a list of examples of phenomena that display wave motion, where possible note whether the wave is longitudinal or transverse.