Mud Flies Off
Classical Mechanics
Level
2
A wheel covered with mud is held mid air. It starts rotating clockwise with its speed gradually increasing. After some time, mud starts flying off the wheel.
In which direction is the mud more likely to fall?
Left
Right
Equally to the left and the right
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1 solution
The piece of mud is forced to a circular orbit. The centripetal force that keeps it on the orbit points towards the axis of the wheel. This force is due to adhesion between the mud and the wheel. When the mud is on the top, gravity points in the same direction, and helps it to remain on the circle. When the mud is at the bottom gravity works against the adhesion, and that is where the separation is most likely. Right before the separation happens the piece of mud moves to the left. Since the velocity cannot change abruptly, after the separation it keeps moving with to the left.