Falling Coffee Cup is Arrested by Friction

A coffee cup is tied to the middle of a pencil by a strong string. The string is drawn up along a bar by pulling the pencil away at about a 45 degree angle relative to the horizontal. When the pencil is released conservation of angular momentum leads to the pencil rapidly wrapping around the bar which generates sufficent friction to arrest the coffee cup before it hits the ground.
UCB Index: 
A+30+55
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