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Cotton Ball Catapult

The transfer of energy from potential energy to kinetic energy is easy to understand (and fun to learn about!) with a catapult. A catapult is a machine that stores energy then quickly releases it to fire a projectile. This activity allows students to build their own catapult and experience how differences in their design relate to the forces on and acceleration of their projectile — a cotton ball!

Objectives

  • Understand the concept of action and reaction forces.

Materials

  • Per Group:
    metre stick
    cotton balls

  • Per Group or per Student:
    1 plastic spoon
    1 ruler
    1 length or roll of masking tape
    2 rubber bands

Key Questions

  • What kinds of forces are at work in your catapult?
  • How is energy converted and stored by your catapult?

What To Do

  1. Challenge students to work individually or in groups to see who can make a cotton ball catapult using only the materials provided.
  2. Once students have made their catapults, test them and use the metre stick to measure how far their cotton balls fly. Here’s one example of what your students might build.

Vocabulary

  • potential energy: Energy stored in an object either due to its position (i.e. in relation to the ground) or condition (i.e. stretched or compressed in a spring or elastic band).
  • kinetic energy: The energy of a moving object. Potential energy is converted into kinetic energy when an object is acted upon by a force.

Extensions

  • Try loading different projectiles into your catapult (such as pompoms and ping-pong balls). Do they go further than the cotton ball? Why or why not? Be careful not to hit anyone with hard objects.
  • How does changing the materials (i.e. thicker rubber bands or more flexible spoons) affect the outcome? Explain your results in terms of forces.