Materials

• Yardstick, meter stick or measuring tape
• Egg
• Rubber bands
• Plastic bag
• Tape
• Chart (PDF)
• Pen

Directions

1. Put the egg inside the plastic bag and seal the top closed with tape.
2. Tie one rubber band to the end of the plastic bag.
3. Hold a measuring stick to the wall to find a point about one meter (or three feet) from the floor. Make sure the “0” end of the measuring stick is up on the wall, not at floor level.
4. Hold the rubber band and the egg at the “0” point of your measuring stick. Keep holding the rubber band at this point while you drop the egg. Note how far down the measuring stick the egg fell. Write your findings in the chart.
5. Drop the egg two more times and record how far it falls each time. Calculate the average distance as noted in the chart.
6. Tie another rubber band to the bungee cord. Drop the egg again, and measure and record your findings three times.
7. Repeat these steps with three and then four rubber bands tied to the bungee cord. Record all your findings in the chart, and calculate the average distances.
8. Based on the data collected, estimate how many rubber bands you’ll need to drop the egg from two meters (or six feet). The egg needs to get as close to the ground as possible without touching the floor. Think carefully – you’ll only get one chance to test your prediction!
9. Use your measuring stick to mark a point two meters (or six feet) on the wall. You can mark this point with tape. Tie the number of rubber bands you think you’ll need based on your prediction.
10. Stand on a chair. Hold the rubber band to the wall at the marked point and let the egg drop. How did you do? Was your prediction right?

What's happening?

Before the egg fell, it possessed gravitational potential energy and no kinetic energy. At the end of the drop, the egg and rubber band system now possess less gravitational potential energy, no kinetic energy (it is not moving) and a lot of elastic potential energy due to the stretched rubber bands. This illustrates the Law of Conservation of Energy. Most of the initial gravitational potential energy transferred to elastic potential energy at the bottom of its fall. Some energy also went to heat energy.

Extension

Discuss these guiding questions:

• What type of rubber band are you using? Does it make a difference? Explain.
• Do you have to use the same rubber band throughout? Why or why not?
• Does it make a difference if you throw the egg down or just let it drop? Explain.
• What are the different forms of energy illustrated in this activity
• What happens if you add too many rubber bands? Too few?
• How would you summarize the transfer of energy?
• How do you think bungee jump creators test the length of a bungee cord for a human bungee jump?

Vocabulary

Elastic potential energy
Energy stored in elastic materials

Gravitational potential energy
Energy an object possesses because of its position in a gravitational field

Kinetic energy
Energy from motion