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Rubber Band Heat Engine

based on 13 ratings
Author: Erin Bjornsson

An engine is a machine used to transform one kind of energy into another to produce work. In this project, we'll learn how to make a rubber band heat engine, a type of engine that converts thermal energy, or heat, into mechanical energy, or movement.

Typically, things expand (get bigger) when heated, and contract (get smaller) when cooled. Have you ever heard creaking sounds in your room at night? These come from the floorboards contracting due to the drop in temperature that usually accompanies the sun going down.

However, this rule doesn’t apply to rubber! The molecular structure of rubber is very complex: Imagine a bunch of molecules linked together in a “chain” that resist being stretched when pulled on. This “stretchiness” enables rubber to be used in erasers, bicycle tires, and bungee cords. However, this chain-like structure also causes rubber to behave rather unusually during temperature changes.

Problem

What kind of work will a rubber band perform when its heated and cooled?

Materials

  • Rubber bands of different thicknesses
  • Scissors
  • Heat lamp
  • Ice cube
  • Coin
  • Hammer and nail
  • Push pin
  • Duct tape
  • Ruler
  • Plastic spool from a roll of tape (a roll with a gutter works really well; these can be acquired from certain rolls of electrical tape or PTFE tape)

Procedure

  1. Hammer a nail about a foot above a desk or countertop that is close to an electrical outlet (so that you’ll be able to plug in your heat lamp later). Ask an adult before making holes in the wall! Leave an inch or two of the nail sticking out of the wall.
  2. Take the tape roll and hang it over the center on the nail so it can rotate freely.
  3. Use the scissors to cut a rubber band open so you have one long strip.
  4. Use a thin strip of duct tape to tape the coin to one end of cut rubber band.
  5. Use the push pin to secure the end of the rubber band without the weight to the wall on one side of the tape roll.
  6. Drape the other side of the rubber band with the weight over the tape roll and let it hang freely.
  7. Set up the heat lamp to point at the rubber band. Don’t turn it on yet!
  8. Using tape, mark the starting height of the weight (coin) on the wall.
  9. Rub an ice cube along the part of the rubber band between the tape roll and the push pin. Wait about a minute and record your observations.
  10. Mark the distance (also called displacement) of the coin from its original position on the wall with tape. Use your ruler to measure and record the distance.
  11. Set up your heat lamp so that the bulb is about 3 inches away from your rubber band. Turn your heat lamp on. Wait about two minutes and record your observations.
  12. Mark the displacement of the coin from its original position on the wall with tape. Use your ruler to measure and record the distance.
  13. Repeat the experiment with rubber bands of different thicknesses. Does rubber band thickness affect how much the band will expand or contact?

Results

The rubber band will expand (lengthen) when rubbed with ice, and will contract (shorten) when heated by the lamp.

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