A Question about Flying Clothes Pegs

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SUMMARY

The discussion focuses on the mechanics behind the forward motion of a clothes peg when released after being pressed down. The primary forces at play are the pressing force and its reaction force, as described by Newton's third law. Due to the shape and slipperiness of the peg, the pressing force is not perfectly perpendicular to the peg's axis, resulting in a forward component. The vector sum of these forces contributes to the peg's rapid forward motion upon release.

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  • Understanding of Newton's laws of motion
  • Basic knowledge of vector components
  • Familiarity with force interactions
  • Concept of reaction forces
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  • Investigate historical demonstrations of similar mechanics, such as cherry pits
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When we press down a clothes peg (those big, plastic ones), and then let our fingers slip off it, the clothes peg will snap close and fly forward. Which force and its components are responsible for this forward motion?
 
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Because of the shape and slipperiness of the pegs, it is practically impossible to press down with a force truly at right angles to the peg's axis. So the pressing force, and its reaction force (Newton's third) upward from the surface the peg is lying on have both got components in the forward direction. And the vector sum of those two forces has a double component in that direction. It is this forward force that shoots the peg out.

This same demo used to be done with cherry pits in the old days.
 

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