Pendulum Waves

A wave is a transference of energy from one point to another. Sometimes it can be seen as a pendulum swinging back and forth, other times it is like a flowing up and down motion, and in still other cases it is simply a vibration passed from one particle to another. In this experiment we’ll show you how to measure and discover the properties of pendulum waves.

When Garrett and Harrison move back and forth on a swing they are riding a pendulum. A pendulum is one kind of wave.

There are two major types of waves: mechanical and electromagnetic. Mechanical waves travel through a physical medium like air, water or earth. Electromagnetic waves can travel without physical substance to travel through, like light waves traveling through space.

The speed the wave oscillates at is called its frequency. Everything has a natural frequency, it will vibrate if set in motion. The top of a wave is called the crest and the bottom of the wave is called the trough. The amplitude of the wave is the height of the wave from the bottom of the trough to the top of the crest.

Experiment

Show pendulum waves with a back yard or playground swing. Have one child sit on the swing and slowly swing back and forth without pumping. Time how long each oscillation is from when the swing is in its furthest forward position until it returns to that same position. Now try timing the swinger when he or she is swinging higher. What is the oscillation speed now? How does it compare to the slower swinger?

It is difficult to accurately time one oscillation.  Try timing ten oscillations and then divide by ten to get the time of one oscillation.

You may also want to time another pendulum this way to see how it compares to the swing in frequency.  You could use a yo-yo or a washer tied to a string.

Does the weight on the pendulum make any difference?  Does the length of the string make any difference?

• Where else do you find pendulum motion in everyday life?  Brainstorm together.