Thermodynamics ** 4F30.70 ** Entropy and the second law

Heat cycles

Rubber band motor

Equipment:

• bicycle wheel with spokes replaced by rubber bands - hallway
• 250 W heat lamp - mounted on shelf 12
• support and clamp - hallway

Theory: When a rubber band is heated, it contracts.

Description: The wheel must be well balanced to work properly. When the wheel is out of balance, the "spokes" on the bottom must be tightened (or the ones at the top loosened).

Heat one side of the wheel by placing the heat lamp as close to the wheel as possible. This causes the rubber bands to contract, moving the rim there towards the center, and shifting the center of gravity of the wheel toward the opposite side of the wheel. If the wheel is properly balanced it will rotate slowly.

Setup time: 24 hours, to ensure that the wheel is balanced.

References: (available in the demo room)

• Feynman, "The Feynman Lectures on Physics", vol. I, page 44.2.
• Freier and Anderson, "A Demonstration Handbook for Physics", page H-32.
• Meiners, "Physics Demonstration Experiments", 26-4.1.