A friend of mine is one of the people in charge of winding a clock tower. He was showing my physics class how the tower works, and we were looking at the pendulum.
Here is a photo of the pendulum in question, from this blog.
We asked the class:
Why are there weights on the top of the pendulum?
This may sound like a bit of a trick question; one can come up with many possible reasons. But I’ll tell you that the weights are put there by humans deliberately as they maintain the clock. Sometimes they add a few and sometimes they take a few off.
A student then asked why the weights don’t slip off.
For a given pendulum length and swing amplitude, what is the minimum coefficient of friction to keep the weights from sliding off?