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Energy Transfer Through Balls

In this activity, students learn about energy transfer by observing a demonstration involving balls of different size and elasticity

Elasticity is the tendency of something to return to its original shape if it gets deformed. If something is very elastic, it will do this quickly and with great force. If it's not so elastic, it will do it slowly and with not as much force.

The tendency of a material to return to its original shape makes it possible for an object to bounce. When a highly elastic object hits the ground, it changes shape. Instead of staying in its changed form, an elastic object pushes against the ground to revert to its original shape. This gives the elastic object its bouncy zing, which will vary depending on the material the object is made of.

In this demonstration, energy from one, heavier bouncing ball is transferred into a smaller, lighter bouncing ball, causing the smaller ball to rocket much higher into the air. 

Activity adapted from Science Kids

Objectives

  • Observe the transfer of kinetic energy from one ball to another.

Materials

  • Per Demo:
    large, heavy ball, such as a basket ball or soccer ball
    smaller, light ball, such as a tennis ball or inflatable rubber ball
    gym or outdoor space with a firm, flat ground

Key Questions

  • Did both balls fall at the same rate?
  • What happened when the larger ball hit the ground?
  • How did the height of the bounces differ between dropping the balls individually and then together?
  • Where did the upward kinetic energy of the smaller ball come from?
  • Can you think of any real-life instances where this phenomenon happens? (e.g. checking in hockey or double-bouncing on a trampoline)

What To Do

  1. Drop each ball from the same height, and notice how high each bounces back up.
  2. Now, place the smaller ball on top of the larger one, holding them together. Ask the class to make predictions about will happen when you drop the two as a unit.
  3. Let go of both the balls at exactly the same time and observe what happens.

Extensions

  • Try reversing the balls, placing the larger one on top of the smaller ball. What do you predict will happen? Try it! Do you get the same result?
  • Experiment with other combinations: a tennis ball and a superball, a yoga ball and a softball, two small balls, two big ones…

Other Resources

Science World | YouTube |Energy Transfer Through Momentum