To demonstrate how heat causes the expansion and contraction of materials by creating a heat sensor.
Thermal Expansion results when matter changes volume in response to a rise or drop in temperature. As materials are exposed to heat, constituent particles begin to move around rapidly resulting in a greater average separation. The level of expansion varies with temperature, but can be determined by the materials coefficient of thermal expansion (the degree of expansion divided by the change in temperature).
- Rubber band
- Wooden block of wood. The wood block should be large enough for the rubber band to fit tightly around, but small enough not to snap the band.
- Large pin or thin nail
- Poster board or cardboard
- Matches or other direct heat source (such as a candle or lighter)
Estimated Experiment Time
About 15 minutes
- 1. Cut the shape of an arrow from your poster board or cardboard. The arrow should be about the length of your wood block.
- 2. Take your rubber band and stretch it around the outer edge of your wooden block so it's snug.
- 3. Push your pin through your arrow at the center of the arrow base (the side opposite the arrow triangle).
- 4. Carefully place the pin under the rubber band, centered along one of the edges of the block. Your final heat sensing unit should look similiar to the reference figure.
- 5. Light a match and carefully bring it close to the rubber band, closest to the pin.
- 6. The cardboard arrow will begin to rotate slowly anti-clockwise.
- 7. Place the match on the opposite side of the pin.
- 8. The cardboard arrow will begin to rotate clockwise.
Be very careful when playing with fire! This experiment requires adult supervision and assistance at all times and should be conducted in a safe location, free of any flammables. Also be careful not to touch the rubber band with your heat source, otherwise it may snap.
Why is it the arrow rotates then the heat source is pushed close to the rubber band? Can you think of a suitable replacement for the band that would prevent the experiment from functioning? How do you think you could change this experiment around to create a Cold Sensor? Can you think of any real-world object you observe every day that reacts to the expansion and contraction from hot and cold?
The heat from the heat source causes the rubber band to contract which rotates the pin and subsequently the arrow. When the heat is moved to the opposite end, the heated spot is changed and the air around the pin becomes cooler while the heat around the new spot becomes stronger. What's happening is the rubber band is contracting around the heat source while it's expanding around the areas that are cooled.
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