Physics Demo Number: 025

Approximate Run Time: 10 min

Newton's 3rd with a Claw-Hammer and Hinged-Board

Demo Description

Hang a hammer from a hinged board, then lift the board and twist the hammer to find a new equilibrium.

Scientific Principles

Newton's 3rd Law of Motion - action/reaction pairs using torques in equilibrium.

 

Equipment

  • Hammer

  • Hinged board

  • Set up stand

  • Mass

 

Equipment Location

  • The apparatus is located in Kit (025) on [F-1-5]

  • Set up stand next to door into 4327

1

2

3

4

Instructions

The photos show the demo mounted on a set-up stand and shadow projected with the overhead transparency projector to help students sitting high above the lecture desk to see the nature of the apparatus more easily.

Obviously the situation in the photo 1 is what one would predict seeing for these components. However by holding the hinged board horizontal and twisting the hammer around so that its handle is 180 degrees from its original configuration relative to the hinged board, one discovers the new equilibrium position shown in photo 4.

Note that hammer is prevented from freely rotating about the axis of the string( through the fourth hole ) by the contact force between the board and the handle butt. The third law says that the handle butt must exert an equal and opposite force on the board. This reaction force is precisely what is needed to give a clockwise torque on the board to hold the other two counter-clockwise torques on the board in equilibrium.

 
Writeup created by David A. Burba
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