Rubber Band Experiment: Stretch into Physics!

Stretch your science knowledge with this experiment that defies the laws of physics. Will heat make a rubber band expand and get longer or contract and get shorter?

Supplies
An empty, 2-liter soda bottle
Permanent marker
Scissors
Pencil
Small, thin rubber band
A handful of quarters (20-25)
Tape
Paper clip
Hot tap water
Ice cubes
Large shallow bowl or pan
Work area that won’t mind spills
Dish towel or paper towels

Directions
1. Use scissors to cut off the top of a two-liter soda bottle. You will want a cylinder shape that stands on its own.

2. Cover any sharp edges around the top rim of the bottle with tape.

3. Carefully use the scissors to poke 2 small holes (just large enough for a pencil to pass through) on opposite sides of the bottle. The holes should be about one inch below the top edge.

4. Poke the pencil through one of the holes from the outside of the bottle.

5. Place the small rubber band onto the pencil.

6. Once the rubber band is hanging from the pencil, push the pencil into and through the hole on the other side.

7. Tape together a stack of about 20 quarters. Partially unbend a paper clip to use as a "hook." Tape the paper clip to the stack and use it to hang the quarters from the rubber band.

The number of quarters you need will depend on the size and strength of your rubber band. You want the stack to visibly stretch the rubber band, but you do not want your quarters to hit the bottom of the bottle. A strong rubber band may require more quarters, a weaker rubber band may require fewer.

You can also spread out the quarters to make them easier to hang—try two stacks of 10 or four stacks of 5 instead of one big stack of 20 quarters. If you use more individual stacks, you may need to make another paper clip “hook.”

8. Place your two-liter bottle into a shallow bowl or pan in case of spills.

9. Fill the bottle up to the pencil with very hot tap water so the rubber band is completely submerged. Wait a minute or two for the rubber band to become the same temperature as the water.

Make a Hypothesis: What do you think will happen to the length of the rubber band?

10. Look at the bottle from the side. Adjust where you look in so your eyes are at the level of the bottom of the rubber band. Use a permanent marker to draw a line on the side of the bottle where you see the bottom of the rubber band. Label this length "Hot."

11. Now, add ice cubes to the water and stir gently. (This will make the water rise, so some water may spill out of the holes you poked for the pencil. No fear! You prepared for this.)

12. Continue to add ice cubes, stirring frequently, until the bottle and water feel very cold.

Make a Hypothesis: What do you think will happen to the length of the rubber band when it’s cold?

13. Look at the side of the bottle again just as you did before, eyes level with the bottom of the rubber band. Draw a new line where the bottom of the rubber band is and label it "Cold."

Which temperature made the rubber band longer? "Cold" or “Hot”? Does this match your hypothesis? Why do you think this happened?

Bonus: If you want to double up your results, try other methods of heating and cooling instead of using hot and cold water. For example, heat the rubber band with a hair dryer and measure. Then try leaving the bottle in your refrigerator for a half hour and measure.

Do your results match?

Analysis
Were you surprised by your results? You may have learned in science that matter expands when heated, but rubber bands actually expand when they get colder! This happens because of the molecular structure of rubber.

Rubber is made of polymers (long chains of molecules), so when the long chains get hotter, they vibrate. Imagine holding a rope by one end and wiggling it back and forth. This action of creating a wave in the rope causes the rope not to reach as far toward the ground. This is exactly what happens to the chain of polymers in rubber. The heat creates vibrations like waves in the chains. All of this causes the material to contract or get smaller. When the polymers or chains cool down, they relax and stretch out, causing the material to expand and get longer.

Source: Scientific American