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Harmonograph

How can friction and motion combine to make a pattern? Watch the harmonograph draw an intricate pattern that can appear to pulsate in places due to Moiré interference. Best of all, you can take one home with you when it’s finished.

Explanation

The four pendulums on this harmonograph are attached to the platform’s corners so that the platform acts as a giant pendulum that is able to twist as well as swing back and forth.

These motions allow the harmonograph to create intricate patterns (known as harmonograms). As the pen rubs on the paper, some of the platform’s energy is lost as friction, slowing the platform down. The curves being drawn will get smaller and smaller (decaying), creating an intricate pattern.

These patterns are Lissajous curves. The ABC’s logo is a Lissajous curve. You can also find the intricate harmonogram-like patterns on bank notes as they are hard to forge.

Extras for Experts

Lissajous curves were named after the French physicist Jules Antoine Lissajous. He attached mirrors to tuning forks to make them vibrate at particular frequencies. He then shone a light onto the mirrors, which were set so they were perpendicular to each other.

The combination of vibration frequencies caused the light to trace out harmonic Lissajous patterns (seen through persistence of vision). The same principle is used to create laser light shows.

Lissajous curves are also known as Bowditch curves, as they were first investigated by Nathaniel Bowditch.

Questions to Ask

Has anyone played with a spirograph before? How do you think you could make a similar pattern using a pendulum?

Further Reading

Harmonograph
The motion of the four pendulums creates intricately complex patterns and shapes.


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