1N20.10 - See-Saw Center of Mass

Code Number:
Demo Title:
See-Saw Center of Mass
Conservation of Momentum/Center of Mass
Area of Study:
2" X 4" Fulcrum, Pasco Dynamics Track, and Pasco Dynamics Carts with Compressible Springs.

Balance the Dynamics track on the 2 X 4 fulcrum. Place two carts on the track in a position such that the whole system is balanced on the fulcrum. One of these carts has a compressed spring. When the spring is released the carts will spring apart and travel to the ends of the track. As they are traveling, the whole system is still in balance. This will remain true even if more mass is added to one cart.

  • Fritjof E. Christensen, "Toward Improved Apparatus and Better Experiments", TPT, Vol. 12, # 9, Dec. 1974, p. 564.
  • Herbert H. Gottlieb, "Balanced Dynamic Carts", TPT, April 1967, p. 173.
  • Robert Ehrlich, "F.17, Ball Rolling on a Balanced Beam", Turn the World Inside Out, p. 84.
  • David Kutliroff, "57, Motion of Center of Mass Is Not Affected by Internal Forces", 101 Classroom Demonstrations and Experiments For Physics Teachers, p. 127.
  • Borislaw Bilash II, David Maiullo, "Seesaw Carts", A Demo a Day: A Year of Physics Demonstrations, p. 156.
  • George Freier, "A New Reaction - Cart Demonstration", AJP, 33 # 1, XXV, Jan. 1965

Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.