Jumping Discs, 4A30.40

Topic and Concept:

• Thermal Properties of Matter, 4A30. Solid Expansion

Location:

• Cabinet: Thermodynamics Cabinet

• Bay: (A3)

• Shelf: #3

Abstract:

Also called hopping discs or bimetallic jumpers, this demo consists of various jumping discs.

Important Setup Notes:

• N/A

Setup and Procedure:

1. Hold the Jumping Disc in your palm.
2. Rub the silver side with your thumb until you feel warm. Then press down on the silver side until it clicks and make sure that it stays in the clicked-in position.
3. Put the Jumping Disc on a cool, hard smooth surface such as the lecture table with the silver face down.
4. Stand back! The Jumping Disc will jump into the air.

Cautions, Warnings, or Safety Concerns:

• Do not put the Jumping Disk on wooden furniture as it may scratch the surface. It is so powerful in its reaction.

Discussion:

The Jumping Disk is a bimetallic disc that consists of stainless steel on one side and invar(nickel-iron alloy)on the other. The coefficient of linear expansion of the invar is much lower than that of the stainless steel. When you rub the silver side (stainless steel), heat produced by friction causes the bimetallic disc to expand. When the disc is placed on the table, cooling makes it contract. The change from the warm and cool caused the bimetallic disc to change shape immediately and jump into the air because the two surfaces contract at highly different rates due to the change in difference in their respective coefficients of thermal expansion.

Videos:

• Lecture Demonstration's Youtube Channel

References:

• Wikipedia - Thermal Expansion

• Wikipedia - Coefficient of Thermal Expansion

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