Day 117: Batman on Belay

Wednesday, 15 February 2017

If Batman goes rock climbing with a top rope setup, should he use a pulley or a loop at the top? Why?

I set up this demo in my classroom with a 220-g Batman toy. With the pulley at the top, Batman needed a belayer of at least 220 grams to keep things balanced. That’s pretty much what I expected — the pulley is near-frictionless so the weight of Batman and his belayer need to be approximately equal to achieve equilibrium.

But stuff got weird when I switched out the top attachment for a loop. The belayer could be as light as 100 grams. The friction going through that loop, am I right?!

This is in preparation for a Physics of the Challenge Course project we’re starting next week.