The last class I taught was about pendulums, those mundane things that swing back and forth. My favorite illustration of how a pendulum works is the old-fashioned metronome. I still own one like this, somewhere. The lower on the stick you position the weight, the faster the tempo it marks. The one in the picture would be ticking so fast it would be hard to keep up.
This phenomenon illustrates the fundamental principle behind pendulums: that the period of a pendulum (that is, the time it takes for it to swing back and forth) depends on its length, not on the weight or on the angle at which it is released (for small angles). When you move the weight up and down the stick of the metronome, you change the length of the pendulum, and thereby change its period and the tempo it is providing. Nowadays, with metronome apps changing the tempo at the push of a virtual button on your phone, this concept is going to be harder for young musicians to intuit.
Our students made their own pendulums and varied each of the three parameters (length, weight, and angle) to figure out which made a difference in the period of the pendulum. There were brightly-colored chains, with weights hanging on them, attached to protractors and hooks all around the classroom.
One type of pendulum that many students were already familiar with was a kind that you often see in science museums, called a Foucault’s Pendulum. This pendulum, hung on a fixed pivot that does not rotate, was first used to observe and measure the rotation of the earth. This video provides a good explanation of how that is done:
Only a week later, I found myself at Griffith Park Observatory in Los Angeles, and they have a Foucault’s Pendulum in the lobby there. This picture was taken looking down on the pendulum bob as it swings. The bob itself is lighted, as is the circle around it that enables observers to see the change in the pendulum’s position throughout the day as the Earth rotates.
For the Mundane Monday Challenge #131.