Physics Dept. Demonstration Manual

DLD05A - Action and Reaction, Cannon Car

Objective:

To illustrate Newton's Third Law of Motion, using revised devices.

 
Apparatus:  
  • Modified 'Friction Cart,' with Launch tube Bolt, with captive spring, and groove
  • Small steel plate, notched
  • Piece of wood, 8" long (used as mallet)


Method:

Insert the bolt/spring in the launch tube, with threaded end toward the brass washer.

Install the steel plate over the protruding end of the bolt, while facing the smaller slot downwards.

Grasp the threaded bolt with the fingers and pull against the spring pressure until the groove in the bolt is visible.

Pull the steel plate upward to engage the smaller slot with the groove. (CAREFUL! The bolt is now 'armed.')

Set the cart on the floor or a long table.

Using the wood piece, carefully tap the top edge of the steel plate until the bolt is released.

Observe that the cart is accelerated backwards at the same time the bolt is ejected forwards, confirming Newton's Third Law.

Notes:

  1. Ensure that the bolt has a clear, safe path; it could be considered dangerous while armed.
  2. Retrieve the bolt assembly and the steel plate after each use.
  3. A certain amount of practice is recommended in arming the bolt.