Concepts

Thermal expansion/contraction, entropy

Overview

A wooden metre stick, with a pivot closer to one end of the stick, is held down by rubber bands on the shorter end such that the the other end barely touches the table. As the rubber bands are heated up by the heat gun, the polymers making up the rubber band experience an increase in entropy. This causes the rubber band to contract and shorten. As a result, the longer end of the metre stick is lifted off the table.

Details

Equipment

• [1] Wooden metre stick
• [1] Pivot
• [1] Lab stand
• [1] 90-degree clamp
• [1] Aluminum bar
• [1] Heat gun
• [2] #33 Rubber band
• [1] 50 g mass

Classroom Assembly

1. Place the pivot, with a metre stick attached to it, on the table and clamp the pivot at about the 81 cm mark.
2. Place the lab stand near the shorter end of the stick, clamping the bar directly under the metre stick.
3. Loop 2 rubber bands around both the stick and the bar.
4. Hang the mass on the end of the long side of the stick.
   
5. Adjust the height of the clamp such that the longer end of stick barely touches the table.
6. Plug in the heat gun.

Important Notes

• Be sure not to put the heat gun too close to the rubber band while heating it
• Give the rubber band some time to cool down before touching it
• Cool the heat gun with the "Cool" mode until the exhausted air is not scalding hot

Script

1. Set the heat gun mode to "Hot" and heat up the rubber bands evenly.
2. Observe the longer end of the stick is slowly lifted off the table.
3. Set the heat gun mode to "Cool" to cool down the rubber bands.
4. Observe the stick's height decreases gradually until it touches the table.
5. Turn off the heat gun.

Additional Resources