4A30.40 - Spencer Disks

Code Number:
4A30.40
Demo Title:
Spencer Disks
Condition:
Good
Principle:
Expansion & Contraction with Temperature Variation
Area of Study:
Heat & Fluids
Equipment:
Spencer Disks - Jumping Disks (Bimetal Disks) and Aluminum Block.
Procedure:

Warm the jumping disks with your hand and press it to the click position.  Set the disk on a cool level surface.  In a few seconds the transfer of heat from the disk to the level surface will cause the bimetal disk to snap back to its original position causing the disk to jump into the air as it does so.

This demo may be enhanced by using an aluminum block heat sink that has been placed in the freezer for several hours.

References:
  • Ed McNell and Earl Zwicker, "Newton's Laws with Jumping Disks", TPT, Vol. 26, #5, May 1988, p. 308.
  • "H-122. Jumping Disks", DICK and RAE Physics Demo Notebook, 1993.
  • G. D. Freier and F. J. Anderson, "Ha-11", A Demonstration Handbook for Physics.
  • Robert Ehrlich, "I.3. Bimetallic Jumping Disks", Turning the World Inside Out and 174 Other Simple Physics Demonstrations, p. 114 - 116.


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.