How far can you fling a marshmallow?
What you will need:
- 9 craft sticks
- 4-6 rubber bands
- 1 plastic spoon
- a few marshmallows or other small items to launch
Here’s what to do:
- Stack 7 of the craft sticks together and wrap one rubber band around each end of the stack to hold it securely.
- Stack the 2 remaining craft sticks together and wrap a rubber band around one end.
- Hold the pair of craft sticks open so they make a narrow V and slide the larger stack of craft sticks inside the V perpendicularly. Let the top stick from the V rest on the larger stack.
- Tie a rubber band around the top arm of the V and the stack of craft sticks in a crisscross fashion to hold the two pieces together. The closer the stack is tied to the rubber banded end of the V, the more leverage the catapult will have.
- Use the remaining rubber band(s) to secure the plastic spoon to the other end of the top arm of the V so the spoon end is just above the end of the craft stick.
- The catapult is ready to use! Try launching ping pong balls, aluminum foil balls, cotton balls, marshmallows, or cereal by placing the object in the spoon, pulling the top of the spoon back while holding the stack of sticks to the table, and letting the spoon go to launch.
Take it further:
- Secure the spoon handle to the craft stick so the launch arm is longer. What happens to the flight distance of your objects? Do they go further?
- Add extra craft sticks to the stack in the middle of the V. How does this affect flight distance? Ease of launching?
- Try launching two objects at the same time. What happens to the flight distance? Do they go the same distance? Do they go as far as one object alone?
- How can you design and adjust your catapult so it hits the same target each time?
- Try redesigning your catapult, or building a new one, in a different way. (See photos for some ideas.) Compare catapult performances.
What’s going on?
A catapult is a simple machine called a lever. The stack of craft sticks on one end of the catapult is called a fulcrum while the spoon and the craft stick it’s attached to are the lever arm. When the spoon is pulled back, it has potential (stored) energy. When you let go that potential energy becomes kinetic (motion) energy and the object and lever arm fling forward. Most of the energy is transferred to the object you are catapulting, which flies across the room.
Adding more sticks to the fulcrum and extending the length of the lever arm both give you more distance to pull the lever back and therefore it can store more energy. That means there’s more potential energy to turn into kinetic energy when you let go, so your objects fly further.