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!
Understand the concept of action and reaction forces.
Per Group or per Student:
1 plastic spoon
1 length or roll of masking tape
2 rubber bands
- What kinds of forces are at work in your catapult?
- How is energy converted and stored by your catapult?
What To Do
- Challenge students to work individually or in groups to see who can make a cotton ball catapult using only the materials provided.
- 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.
- 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.
- 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.