How the Hub Paradox Works

Leave most objects on top of a turntable and spin it, and they'll fly away in no time. Do the same with a ball, though, and it somehow manages to roll on top for a while without falling. [Steve Mould] set about unpacking this "turntable paradox" in a recent YouTube video.

In the base case, the fact that the marble is rolling is what keeps it on the turntable. When the turntable spins, the ball spins in the opposite direction, according to Newton's first law of motion. As long as the ball is allowed to roll at the same speed as the turntable, it will remain virtually in place in the absence of any other disturbing force. In the event the ball is pushed along the turntable, however, it soon finds itself in a more complicated circular motion, orbiting in a ratio to the speed of the turntable itself. [Steve] explains the mechanics involved and dives into the math behind what's going on.

Sometimes demonstrations like these can seem like simple curiosities. However, understanding physical effects like these has been key to the development of all sorts of complicated and fantastical machines. Video after the break.