Fast and Easy Science Fair Projects: Swinging Good Time

Pendulum motion

Purpose: The properties of pendulums will be investigated.

Overview: When a weight is hung by a wire or a string that is tied to a fixed point ( a point that doesn't move), it is called a pendulum. If the weight is pulled to one side and then released to fall freely, it will swing back and forth. Gravity pulls it down, the momentum keeps it moving past the "at rest" hanging point. Eventually, the weight will stop swinging back and forth because friction with the air will slow it down. (Pendulums have been used since 1657 in clocks, because of the regularity swinging motion.)

Hypothesis: Hypothesize that when the weight (mass) tied to a string is greater than one tied to another string of the same length, the heavier weight will swing longer.

You need:

• 2 chairs
• string or strong thread
• 5 identical large metal washers (for weights)
• hardbound book
• long stick or pole
• scissors

Procedure: The Constant in this project is the length of the string. The Variable is the mass (or weight) at the end of the pendulum string. Place two chairs back to back and a short distance apart. Lay a long measuring stick or pole across the tops of both chairs. Tie two pieces of string onto the stick some distance apart so the hanging strings almost touch the floor. Cut the strings to an equal length an inch or two (2-4 cm) from the floor. At the end of one string, tie four large metal washers. At the end of the other string, tie one large metal washer, making sure that the bottom of the washer is at the equal height from the ground as the group of four washers. In starting the pendulums swinging, you must make sure they are both released exactly at the same time. To do this, let the washers rest on a hardbound book and lift and pull them both, on the book, to one side of the chair, perhaps to seat level height. Keep the two hanging strings taut. Drop the book down and and both pendulums will begin swinging exactly at the same time. What happens then? Do they both swing at the same rate? Does the pendulum that has four washers swing four times longer than the pendulum that has only one?

Results and Conclusion: Write down the results of your experiment. Come to a conclusion whether or not your hypothesis was correct.

Something more: 1) How does the length of the string affect the pendulum's swing? If the weights are the same but one pendulum's string is twice the length of the other, will it swing twice as long? Use the same chair set-up above, but take the string that had four washers on it, cut it in half, and tie just one washer to it, Start them swinging at the same time, (you will have to hold one in each hand and let go at the same time as best as you can, since you can't get them started together by letting them slide off a book as we did before.)

2)Think of other questions about pendulums that you can investigate and use your chair set-up to find the answers. For example, if both the strings are the same length and both weight are the same but one pendulum is pulled back farther/higher when they are set to swinging, will the one pulled back farther swing longer?