Physics Dept. Demonstration Manual

DHT05 - Jumping Disc

Objective:

To illustrate different thermal expansions of different metals.

 

Apparatus:  
  • Two aluminum heat reservoirs
  • Semi-circular rod
  • Two hotplates
  • Bimetallic disc


Method:

The two heat reservoirs are placed on Hotplates about 2 feet apart. Only one Hotplate is turned on, full. The bimetallic disc is thredded on the hooped rod such that the concave side contacts the hot reservoir. After about 20 minutes of heating, differential thermal expansion causes the disc to turn "inside-out" abruptly, propelling it along the rod to the cold side, where it cools and snaps back to the hot side et al.

Notes:

  1. Hotplate is very hot, caution.

  2. One side of disc: stainless steel. Other side: Invar alloy (Invar: 36% Nickel, 64% Iron)