Phone Book vs. Paper

Objectives

• Describe gravitational force, and how this force pulls objects towards the Earth at the same rate, regardless of mass.

Materials

• Two balls of different masses (e.g. tennis ball and basketball)

• Telephone Book

Key Questions

• How does gravity act on the two balls?
• How do you predict gravity will act on both the phone book and paper?
• What are the differences between the phone book and the paper?
• What forces are acting on the phone book and paper when they are dropped?
• How might the results of your activities differ if you did them in space, where there is negligible air resistance?
• What is drafting, and how is it used in sports?
• What is inertia?

What To Do

1. Hold two balls of different masses from the same height, and have the class make a prediction of which will hit the ground first. Try it. Are they surprised to see them hit the ground at the same time?
2. Rip out a page from the telephone book and ask the class which is heavier: the telephone book or the piece of paper. If you were to drop both at the same time, which one would the class expect to hit the ground first? Make a prediction and test out each of the following:

• Place the paper underneath the telephone book and drop them simultaneously.
• Place the paper on top of the telephone book and drop them.
• Crumple up the piece of paper into a ball. Hold the ball and phone book side-by-side and drop them simultaneously. Were students surprised which one hit the ground first?

Extensions

• Want to see what happens in space? Check out this video
• See a feather and bowling ball drop in a vacuum chamber.