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Pendulum Waves

based on 6 ratings
Author: Christopher Crockett

Sometimes, physics can be used to create beautiful art. Kinetic art is art that relies on motion to achieve a specific effect. Often that motion is just an application of simple laws of physics. Waves and harmonic motion (some examples include pendulums and springs) are often great sources of inspiration for creating mesmerizing displays.

In this project, you will use the laws of simple pendulum motion to create a “pendulum wave apparatus”: a device where many pendulums of different lengths (and therefore different periods) start swinging at the same time. As they move in and out of sync, the pendulums create a sequence of cycling visual wave patterns.

Problem: Build a pendulum wave apparatus.

Materials

  • 2 meter sticks (or a meter stick and a ruler or tape measure)
  • 3.5 meters of string (roughly)
  • Nine weights that can be easily attached to a piece of string (e.g. nuts, washers, masses with hooks)
  • Tape
  • Two stacks of books, each at least one meter high

Procedure

  1. Cut nine pieces of strings with the following lengths: 44 cm, 41 cm, 39 cm, 37 cm, 35 cm, 33 cm, 31 cm, 30 cm, 29 cm.
  2. Starting at about the 10 cm mark on the meter stick, tie a piece of string at each point located every 9 cm along the ruler (roughly). Use a small piece of tape to help secure each piece of string to the stick.
  3. Use the two book stacks to support both ends of the meter stick. The meter stick should make a “bridge” connecting the books.
  4. Attach one weight to the free end of each string. Thread the string through the hole or hook on each weight and, using your ruler or tape measure, adjust the lengths to exactly match the following table, starting with the longest string. Once you get the lengths right, tie the string to the weight.

Pendulum

1

2

3

4

5

6

7

8

9

Length (cm)

35.7

33.0

30.6

28.5

26.6

24.8

23.2

21.8

20.5

 

  1. Once you have all nine pendulums constructed, use the ruler (or a large book or even your arm) to scoop all the pendulums towards you by a few inches.
  2. Let all the pendulums go at once so that they swing perpendicular to the meter stick from which they are hanging.
  3. Enjoy the show! It’s best to watch the pendulums either from above (looking down) or from one end of the meter stick (viewed along its length). How many different patterns do you see? Does anything repeat? If any patterns do repeat, how long does it take for them to do so?

Results

The pendulum ensemble will cycle through a number of patterns over a 30 second interval. You’ll see everything in sync, pendulum waves of varying lengths rippling down the line, alternating swings (half the pendulums going one direction, half going the other), and even seemingly chaotic motion.

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