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Phone Book vs. Paper

Students are introduced to the force of gravity, and see that objects fall at the same rate, even if their masses are different.

Although gravity pulls harder on big, heavy objects, they're harder to get moving than light ones. Therefore, objects that are the same shape will fall at the same rate, even if one weighs more than another. Shape can make things tricky because big, flat, light objects (like a flat sheet of paper) are slowed down more by air resistance than are smaller, smoother objects.

Vocabulary:

  • Gravity: The forces of attraction which the Earth has for objects on its surface; also the force of attraction between any two objects.
     
  • Friction: The resistance a body meets when moving over a surface or through a gas or liquid; the force that resists the motion of two surfaces that are touching each other.
     
  • Air Resistance: The friction caused by an object moving through air.
     
  • Drafting: A technique used in sports, where an athlete or car races behind someone else to take advantage of the reduction of air pressure/resistance.

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

Other Resources

Science World Resources | Full Lesson & other activities | Forces
Science World at TELUS World of Science | School Programs | Roller Coaster