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In this activity, a marking pen remains stationary while a platform swings beneath the pen, acting as a pendulum. As the platform swings, the pen marks a sheet of paper that is fastened to the platform, generating beautiful, repetitive patterns, which grow smaller with each repetition. These colorful designs contain hidden lessons in physics.
Note: Rather than providing detailed instructions for assembling this device, we have chosen instead to supply some close-up photos and the following helpful hints. The rest is left to the dedicated experimenter.
Once your Drawing Board is adjusted, you can create wonderfully intricate designs. Push the board to start rotational as well as translational motion; lower the pen to start drawing and raise it to stop. Try drawing one to four patterns on the same paper using pens of different colors, changing the direction and force of the push with each new color.
When you push on the platform, displacing it from its resting position, the four suspending strings exert forces on it to bring it back. You can think of these forces as acting in two directions perpendicular to each other: north-south and east-west, for example. The combination of these two simultaneous motions can produce a variety of curved forms, in the same way that careful use of the two knobs on an Etch-a-Sketch toy allows you to draw curves.
The diminishing size of each successive repetition of the pattern is a graphic demonstration of how friction steadily dissipates the energy of a moving object.
Some of the shapes you will produce with the Drawing Board are known as harmonograms, or Lissajous figures. An oscilloscope can easily produce these figures because the pattern on the scope face is generated by a single electron beam simultaneously moving vertically and horizontally on the screen. An oscilloscope can be thought of as an electronic Etch-a-Sketch.
One of our teachers had this Snack set up and running during an aftershock of California’s 1989 Loma Prieta earthquake. The pen traced the pattern of motion generated by the aftershock. The operating principle behind the Drawing Board—a pen directly attached to the earth with a paper only loosely attached to the earth—is the operating principle behind the seismograph.
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Attribution: Exploratorium Teacher Institute