Spool

Purpose

To illustrate a counterintuitive problem in rotational dynamics.

Equipment

Spool with cord, as photographed.

Images

d1-83

Description

The cord is wrapped around the smaller radius of a spool and placed on a horizontal surface such that the cord emerges over the top side of the spool. When the cord is pulled the spool will move toward the direction of the applied force, the forward direction. Q: When the cord emerges from the bottom side of the spool (as shown in the photograph) how will the spool move? A: Forward, just as in the previous example. This problem can be varied as follows. Imagine a line along the cord such that when the cord is held up at some large angle this line intersects the floor along the line of contact

References

(PIRA 1K10.30)