Table Tricks – The Coffee Cup Pendulum

A pendulum is anything that swings back and forth on a string, chain or rope. Due to their properties, they are good for timekeeping and are found in old clocks. Pendulums are also used for measuring gravity. Pendulums are in Seismometers and even used in religious purposes as a swinging incense burner called a censer. Even a playground swing is a pendulum.

For this experiment, we will start out with a string and 15 washers to make our pendulum. Tie 14 of the washers to one end of the string and the last washer to the other end. To test out the functionality of the pendulum, dangle the string over your friend’s finger. Common sense tells us that the end with 14 washers will crash to the table when the other side is released. Does the pendulum hit the table?

It doesn’t, thanks to the acceleration downward of the heavy end, and the pendulum swing of the single washer. The rotational energy and a little bit of friction will cause the single washer to swing and wrap around the finger. We have found that the sweet spot is using 14 washers to 1 washer in this experiment.

So if it works with washers, what about other objects? Watch the video and see what happens when we try a coffee cup and a spoon and a wedding ring and a wine glass.