You’ll need a pendulum for this experiment. A pendulum is really nothing more than a weight at the end of something that can swing back and forth. The easiest way to make one is to get a string and tape it to the edge of a table. (The string should be long enough so that it swings fairly close to the ground.) Tie a weight to the bottom of your string and you’ve got a pendulum.
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Now, for YOUR part of the experiment we are going to change one of three different things, and only one thing changes at a time. First, we’ll change the length of string and measure the period. Then we’ll change the mass of the object, and then the angle that you start the pendulum from. With each trial you will be changing only ONE of those three things. (The rest of the variables will be constant.)

1. Make an observation. Play with the pendulum a bit and see how it behaves.
2. Make a hypothesis. How will the length of string effect the number of swings in 10 seconds? Will there be more, less, or no change in the number of swings as the string gets shorter.
3. Set a timer for 10 seconds or get someone who has a watch with a second hand to tell you when 10 seconds are up.
4. Now for the test. Pull the pendulum back as far as you’d like (the pendulum swings smoother if you don’t lift the weight higher than the top of the string).
5. Start the timer and let go of the weight at the same time.
6. Count the swings the pendulum makes in 10 seconds. This is your frequency in #cycles per 10 seconds.
7. Write down what you found (collect the data as shown in the video).
8. Do two more trials with the string at that same length.
9. Now change the changing variable. In other words, shorten the string. I would recommend shortening it at least an inch.
10. Redo steps 3 through 9, recording each time.
11. Continue shortening the string and doing trials until you get at least five different lengths of string.
12. Convert frequency to period by taking the inverse. Do this for each trial.

Now report your results. Take a look at your data and see if you find a trend. Do you get more swings as the string shortens, less swings, or does the length of the string matter? Something interesting to notice is that at a certain length you will get 10 swings in 10 seconds or a swing a second. This is why pendulums are used in grandfather clocks. They keep good time!

Click here to go to next lesson on Hooke’s Law.

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