The higher you pitch a ball upwards, the more energy you store in it. Instead of breaking our arms trying to toss balls into the air, let's make a simple machine that will do it for us. This catapult uses elastic kinetic energy stored in the rubber band to launch the ball skyward.
Catapults store energy until you hit the trigger. You store energy in a rubber band every time you stretch it out - the pull you feel from the rubber band is called potential energy. Catapults store potential energy by stretching ropes and rubber bands, and even by bending and flexing the wooden lever. The more energy you pack in, the higher your ball will go.
These simple catapults are quick and easy versions of the real thing, using a fulcrum instead of a spring so kids don't knock their teeth out. After making the first model, encourage kids to make their own "improvements" by handing them additional popsicle sticks, spoons, and glue sticks (for the hot glue guns).
Experiment & Video
Did you know that you can make a catapult out of simple materials like popsicle sticks and rubber bands? After you learn how to put this one together, perhaps you can make a larger model!
- 9 tongue-depressor size popsicle sticks
- 4 rubber bands
- plastic spoon
- something to toss around, like a ping pong ball or wad of aluminum foil
- hot glue gun
Here's what you need to do:
What's Going On?
We're utilizing the "springy-ness" in the popsicle stick to fling the ball around the room. By moving the fulcrum as far from the ball launch pad as possible (on the catapult), you get a greater distance to press down and release the projectile. (The fulcrum is the spot where a lever moves one way or the other - for example, the horizontal bar on which a seesaw "sees" and "saws".)
If they get stuck for ideas, you can show them how to vary their models: glue a second (or third, fourth, or fifth) spoon onto the first spoon for multi-ammunition throws, increase the number of popsicle sticks in the fulcrum from 7 to 13 (or more?), and/or use additional sticks to lengthen the lever arm. Use ping pong balls as ammo and build a fort from sheets, pillows, and the backside of the couch.
Advanced Teaching Tips: For high school and college-level physics classes, you can easily incorporate these launchers into your calculations for projectile motion. Offer students different ball weights (ping pong, foil crumpled into a ball, and whiffle balls work well) and chart out the results.
This project lends itself well to taking data and graphing your results: you and your child can jot down the distance traveled along with time aloft with further calculations for high school students for velocity and acceleration.
Questions to Ask
Does a golf ball go the same distance as a ping pong ball? How about a marshmallow?
How many popsicle sticks can you add to the stack to increase your flight distance?
What if you add a second plastic spoon to make a double-launcher?
What would you change (lengthen, shorten...?) to make the ball fly further?