Updated: 2 days ago
Search for "STEM Projects for Kids" and this classic craft stick catapult design pops up everywhere, and for good reason! It's easy to build, easy to find bulk materials, and it works well with a wide age range. What could be made better?
I see three small but impactful things that can be improved:
Build with the right sized craft sticks (see materials).
Use smaller rubber bands that are easier for young kids to independently wrap around the craft sticks.
Show how to adjust the fulcrum position to get different launch trajectories.
I made a kit of supplies for 30 catapults that includes the best materials I could find: STEM Inventions Catapult Kit, or you can source the parts individually from the list below. I'll also note important qualities for each material.
6''x3/4 Craft sticks - These work best because they're flexible enough to store potential energy but not too flexible so that any goes to waste. 6x3/4'' are also easy to wrap into bundles. Smaller 4.5x3/8'' aren't flexible enough and they're harder to wrap. 8'' jumbo tongue depressors are more expensive without any additional benefits.
Colorful loom rubber bands - Smaller rubber bands only require 1-3 wraps around craft sticks for a sturdy connection. Normal office rubber bands require many more wraps, which can be challenging for young kids.
2oz plastic portion cup - Plastic spoons are often used for this project, but it's too easy for projectiles to fall off when the lever arm is positioned at a steep angle. Portion cups hold projectiles better at holding projectiles, which allows kids to experiment with a wider range of fulcrum positions. Additionally, make sure to get cups that have angled sides. Straight-walled cups won't release the projectile as well.
1'' adhesive squares - For attaching the cups. These are easier to distribute to kids than long pieces of masking tape and usually create a sturdier connection.
For the projectiles, 1'' foam cubes are great because they're dense enough to get launched a satisfying distance but harmless if someone gets struck. The cube shape also prevents it from rolling under furniture or getting lost as easily. Other good options are foam marshmallows.
Step 1: Make the Fulcrum and the Base
Stack 8 craft sticks together and wrap the ends tightly. This will be the fulcrum, or the point at which the lever pivots.
You can make the fulcrum larger or smaller but it's not necessary. As you'll see, the position of the fulcrum can easily adjust the catapult lever arm without adding or removing craft sticks.
8 sticks in height is large enough to change the catapult arm angle without needing to move it along the base too much.
Next attach the fulcrum to another craft stick, which will be the base. Instead of wrapping the rubber band, just loop the rubber band onto the base stick, pull it over the fulcrum, then loop it over the other end of the base. Use two rubber bands for a sturdy connection.
Step 2: Make the Lever Arm
The key to a fast fan-powered car is to make sure it's as lightweight as possible, so this design features only a single paint stirrer as the body of the car.
Use loom rubber bands to attach the wheels to the ends of the paint stirrer. This method is fast and easy, but more importantly it allows the wheels to turn to either side, which changes the direction the car is moving.
Young kids can do this step independently by first putting a rubber band on the paint stirrer, then setting the wheels on top. Pull the rubber bands over the straw and around the end of the paint stirrer again.
Repeat with the second set of wheels, then flip the car over.
Step 3: Basket and Projectile
Attach a 2oz portion cup to the end of the lever arm - you're done!
As mentioned, 1'' foam cubes are great projectiles, but you can also give kids a variety of safe things to test such as ping pong balls, foam marshmallows, and cotton balls. This catapult activity is great for exploring concepts like mass, density, and drag.
Step 4: Experiment, Reflect, and Redesign
To launch: Pinch the sides of the cup, pull down, and release!
One of the best things about this catapult design is how easy it is to adjust the trajectory. Just slide the fulcrum closer or father from the pivot point at the front of the catapult. You'll notice that the lever arm resting position raises and lowers, which changes the release angle of the projectile.
Challenge kids to try launching a projectile as far as possible by finding the best angle, then challenge them to get the catapult to launch as high as possible!