A pendulum is any mass which swings back and forth on a rope, string, or chain. Pendulums can be found in old clocks and other machinery. A playground swing is a pendulum. We're going to do some experiments to find out more about pendulums.
If you pull the mass away from its rest position, so that the string is at an angle, and then let go, the mass will begin to swing back and forth. The length of time it takes the mass to swing all the way over and back, once, is called the period of the pendulum.
All three experiments will examine things we can do to the pendulum that will change the period. Here are the three questions we are asking:
1. Does the amount of mass on the end of the string affect the period?
2. Does the angle you pull pack the string to affect the period?
3. Does the length of the string affect the period?
In these experiments, the dependent variable will always be the time for one full swing, or the period.
The three tested independent variables will be the mass, the angle, and the length of string.
The controlled variables will be the attachment point of the string, the string itself, the method used to time the pendulum, and the variales we are not currently testing. These will remain the same for each test, so that we know they won't affect the results. Visit our variables page for more information.
The experiments are easy to do, and don't require any special equipment. We did them ourselves using some string, a few large nuts, a pen, and a watch, and got good results for all three tests in about 20 minutes.
Here's a list of what you'll need for each group doing the experiment:
- a piece of string at least 1 metre long
- 3 or 4 weights, all the same
- a pen and tape, to attach the pendulum to a shelf
- a watch that counts seconds
- pencil and paper to record the results
It's also easier if you have several people doing the experiments, so that one person is free to time the swings.
When you're ready, here are the three experiments. They are set up such that the answers are not apparent, but there are links to descriptions of what should happen. There is also a page explaining the pendulum equation, for Science 10 students.