A simple catapult is a fun school project that shows how stored energy can make an object move. In this 30 minute build, popsicle sticks, rubber bands, a plastic spoon, and a bottle cap become a mini launcher for soft pom-poms or marshmallows. The project feels like a castle workshop, but it teaches real physics used in levers and machines.
It is safest when only soft items are launched and everyone stands away from the launch path.
The catapult works like a lever, with the stacked sticks acting as the base and fulcrum and the spoon acting as the lever arm. When you pull the spoon down, the rubber bands stretch and store elastic potential energy. When you let go, that energy changes into motion and sends the pom-pom in a curved path called a trajectory.
Changing the lever arm length, rubber band tension, or launch angle can change how far the pom-pom travels.
Key Facts
- A catapult is a simple machine that uses a lever to launch an object.
- A lever has a fulcrum, an effort force, and a load.
- Elastic potential energy is stored when a rubber band is stretched.
- More stretch usually means more stored energy, but too much stretch can break the catapult.
- Distance = final position - starting position.
- Average speed = distance / time.
Vocabulary
- Catapult
- A catapult is a machine that launches an object by using stored energy.
- Lever
- A lever is a stiff bar that turns around a fixed point to move a load.
- Fulcrum
- A fulcrum is the fixed point where a lever pivots or turns.
- Elastic potential energy
- Elastic potential energy is energy stored in a stretched or squeezed object, such as a rubber band.
- Trajectory
- A trajectory is the curved path an object follows after it is launched.
Common Mistakes to Avoid
- Launching hard objects is unsafe because they can hurt people or damage things. Use only soft pom-poms, cotton balls, or marshmallows.
- Pulling the spoon back too far is a mistake because it can snap rubber bands or break the popsicle-stick frame. Test small pulls first and increase slowly.
- Forgetting to measure from the same starting line gives unfair results. Always place the catapult in the same spot before each launch.
- Changing many parts at once makes the test confusing because you cannot tell what caused the new launch distance. Change only one variable, such as rubber band tightness or spoon angle, at a time.
Practice Questions
- 1 A pom-pom lands 45 cm from the catapult on the first launch and 60 cm on the second launch. How much farther did the second pom-pom travel?
- 2 A catapult launches a marshmallow 80 cm in 2 seconds. What is its average speed?
- 3 If two catapults are the same except one rubber band is tighter, explain which one will probably launch the pom-pom farther and why.