Pendulums

A pendulum is simply an object, or 'bob,' swinging freely on the end of a piece of sting. 
The 'frequency' at which the object swings is simply the number of times the bob goes 
back and forth per second. 

Try swinging pairs of pendulums together. Do they have the same frequency? 

You will discover that each pendulum has its own 'natural' frequency that cannot be 
changed by pushing the pendulum harder or softer. What factors effect this frequency?

Try the following: Make all of the pendulums still. Now pull back one of the pendulums 
and let go. Hopefully, one of the other pendulum will start to swing. Why did this 
happen? Which pendulums are swinging? Try this again with other pendulums.

Explanation: When you let one of the pendulums swing (pendulum A), the motion of the 
pendulum causes vibrations in the metal strip supporting the pendulums. The vibrations 
in the metal strip and the swinging of pendulum A each have the same frequency. 
Another pendulum (pendulum B) hanging from the metal strip has the same 
characteristics (mass and string length) as pendulum A. Since both pendulums have the 
same characteristics, they must have the same natural frequency. All of the pendulums 
hanging from the metal strip feel the vibrations of pendulum A, but only pendulum B has 
a natural frequency that matches those vibrations. Thus, only pendulum B starts to swing.