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# Stretchy: How Does Heat Affect the Movement of Molecules in a Rubber Band?

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Source:
Author: Janice VanCleave

### Problem

How does heat affect the movement of molecules in a rubber band?

### Materials

• pencil
• 5-ounce (150-ml) paper cup
• scissors
• ruler
• string
• rubber band about 3 inches (7.5 cm) long
• salt
• blow-dryer (to be used only by an adult)

### Procedure

1. Use the pencil to punch two opposite holes under the rim of the paper cup.
2. Cut an 8-inch (20-cm) piece of string.
3. Tie the ends of the string through each hole in the cup to form a handle.
4. Cut the rubber band to make a 6-inch (15-cm) strip.
5. Tie one end of the rubber band to the handle of the cup.
6. Cut an 18-inch (45-cm) piece of string, and attach it to the free end of the rubber band.
7. Fill the cup about half full with salt.
8. Set the cup on the floor under the edge of a table.
9. Holding the free end of the string on the edge of the table, slowly pull the string toward the center of the table. When the cup is just resting on the floor, tape the string to the top of the table.
10. Ask an adult to hold the blow-dryer, set to high heat, about 2 inches (5 cm) from the rubber band and move it up and down the band.
11. Observe the position of the cup as the rubber band is heated for about 10 seconds.
12. Remove the heat, and observe the cup for about 20 seconds.

### Results

The cup rises slightly off the floor when the rubber band is heated and returns to its original position as the rubber cools.

### Why?

Heating the rubber band causes the rubber molecules to vibrate. The moving molecules separate slightly and slip past each other, causing the band to thicken and become shorter.

### Let's Explore

1. Does the size of the rubber band change the movement of the cup? Repeat the experiment, using bands of various thicknesses. Place a yardstick (meterstick) beside the hanging cup to measure any difference in the movement of the cup. Science Fair Hint: Make diagrams to show the results and display them with the rubber bands.
2. Does the weight of the cup affect the movement of the heated rubber band? Repeat the original experiment, using measured amounts of salt in the cup. Record the amounts of salt and the distances the cup moved when the rubber band was heated.

### Show Time!

Do all solid materials contract (draw together) when heated? Replace the rubber band with a 22-gauge metal wire of comparable length. (Ask an adult to remove any insulation from the wire, Try using other solid materials. The results from this experiment will indicate that the contraction of the rubber band when heated is contrary to the reaction of most heated materials. Heating generally causes molecules to spread apart, and thus the object expands. Include this information in your report, and use photographs of each of the experiments as part of the project display.

### Check it Out!

1. Why are bridges, roads, and sidewalks made in sections separated by cracks?
2. Why does heating the metal lid on a jar with warm water make the lid easier to remove?