Learning Library

# Perplexing Pendulum

### Research Questions

• What is a pendulum?
• What causes a pendulum to move?
• What affects the way a pendulum swings?

A pendulum is swinging lever. It is hung from a fixed point and moves back and forth by the force of gravity. Galileo Galilei discovered that pendulums have a regular motion.

### Materials:

• 2 chairs
• yardstick
• string
• 3 identical fishing weights (bank sinker about 6 to 10 ounces)
• ruler
• marker
• helper
• protractor
• stopwatch
• pencil
• paper

### Experimental Procedure:

1. Gather the necessary materials.
2. Place the two chairs back to back with the yardstick extending between the chairs.
3. Tie each of the fishing weights to a piece of string. Then tie the other end of the strings to the yardstick to make three pendulums. The weights should each be 3 inches above the ground.
4. Number the each of the pendulums 1 through 3 by placing a piece of masking tape on the floor under the corresponding pendulum.
5. At your signal with the help of an assistant, release each pendulum at the exact same time from the following positions while starting the stopwatch: Pendulum #1 at a 90 degree angle from its starting point Pendulum #2 at a 60 degree angle from its starting point Pendulum #3 at a 30 degree angle from its starting point.
6. Use a protractor to help you estimate the angles. Although the angles do not need to be exact, they should be obviously different from each other.
7. Watch the pendulums and take note of the times the pendulums come to a complete stop. Record the times.
8. Repeat step 5 four more times to get a good average and to confirm your findings. To find the average, add the 5 times together and divide by 5.
9. Analyze the date and draw a conclusion.

Terms/Concepts: pendulum: a suspended weight that swings back and forth from one point in a regular motion gravity: a force that pulls something back to the earth momentum: the force of movement inertia: the theory that bodies in motion will stay in motion and bodies at rest will stay at rest unless acted on by an outside force period of a pendulum: one swing of a pendulum over and back bob: the weight at the bottom of a pendulum; A pendulum moves in a regular motion. When its bob reaches the end of its swing, gravity pulls it down. As it comes down it gains momentum which causes it to continue to swing to the other side until gravity again brings it back down and momentum pushes it beyond its resting point.

References:

“What’s a pendulum anyway?” at http://www.calacademy.org/products/pendulum/page1.htm “How Pendulum Clocks Work” by Marshall at http://www.exploratorium.edu/ronh/bubbles/bubbles.html “The Pendulum” at http://muse.tau.ac.il/museum/galileo/pendulum.html “Pendulum” at http://science.howstuffworks.com/pendulum-info.htm

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