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!

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.

### 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.

For younger students, a pictorial “How To” might look like:

Step One: Collect Materials

Step 2: Design and Assemble

Step 3: Test

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.

Survivors

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

Egg BB

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

Comet Crisp

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

T-Rex and Baby

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Buddy the T-Rex

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Geodessy

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Science Buddies

Artist: Ty Dale

From Canada, Ty was born in Vancouver, British Columbia in 1993. From his chaotic workspace he draws in several different illustrative styles with thick outlines, bold colours and quirky-child like drawings. Ty distils the world around him into its basic geometry, prompting us to look at the mundane in a different way.

Western Dinosaur

Artist: Ty Dale

From Canada, Ty was born in Vancouver, British Columbia in 1993. From his chaotic workspace he draws in several different illustrative styles with thick outlines, bold colours and quirky-child like drawings. Ty distils the world around him into its basic geometry, prompting us to look at the mundane in a different way.