This Thursday at Catalina we'll be experimenting with pendulums! There are some interesting forces at work that make a pendulum work properly, including Newton's Law of Gravity and his 1st and 2nd Laws of Motion. What happens if you change the mass of the pendulum bob? Will it change the period (one full swing back and forth) of the pendulum? Here is an easy "recipe" for making a pendulum at home:
Materials:
1.5 - 2 feet of yarn or string
pencil
large paperclip
several small washers
tape
Assembly:
1. Tie a small loop at one end of the yarn.
2. Attach the paperclip through the loop, so that it hangs freely from one end of the loop.
3. Make a slip knot at the other end of the yarn. If you don't know how to do this, here are some simple instructions (click here).
4. Loop 1 washer through the paperclip so it hangs freely below the paperclip.
5. Tape a pencil to a table top so that 1 - 2 inches of the pencil hang over the edge.
6. Hang the slip-knot end of the pendulum on the pencil.
Experiment:
1. Try timing how many periods (full swings) the pendulum makes with only 1 washer for 20 seconds.
2. Now try adding washers to the pendulum bob (the paperclip), one at a time, to see if that changes the number of periods during a 20-second interval. Make sure to swing the pendulum bob from the same height as before. Be consistent!
3. Now use the slip knot to change the length of pendulum by shortening it or lengthening it. Swing the pendulum again from the same height. How many periods occur during a 20-second interval this time?
Does the mass of the bob or the length of the pendulum (or both?) change the number of periods?
