Marshmallow Catapult

What You’ll Create

Engineer a real working catapult from everyday materials and use it to launch marshmallows across the room! 🏹 The build is simple enough for kids to tackle independently but satisfying enough to keep them tweaking and experimenting — adjusting the arm angle, changing the rubber band tension, and measuring distances. It is classic hands-on STEM with an irresistible reward built in.

How to Set It Up

Step 1: Build the Base

Take five straws and bundle four of them together side by side. Wrap several strips of tape tightly around both ends to hold the bundle firmly together — this is your catapult base. Stand it flat on a table. Then take a sixth straw and tape it upright at one end of the base bundle, perpendicular to the base, to act as the pivot support. Add a second upright straw right next to it for extra stability.

Step 2: Attach the Arm

Take a spoon and lay it along the length of a single straw so the bowl of the spoon extends beyond one end. Tape the handle of the spoon firmly to the straw with several overlapping strips of tape — the spoon and straw should feel solid and move as one piece. This straw is your throwing arm.

Step 3: Add the Rubber Band

Loop a rubber band around the two upright straws on the base, about halfway up. Slide the arm (spoon straw) under the rubber band so the rubber band crosses near the midpoint of the arm. Pull the arm down on the spoon side — the rubber band should stretch and create upward tension. If the tension is too loose, loop the rubber band an extra time or use two bands.

Step 4: Launch!

Place one marshmallow in the bowl of the spoon. Hold the base down firmly with one hand. Pull the spoon end down with the other hand — then let go! The rubber band launches the arm upward and sends the marshmallow flying. Measure the distance with a ruler and try to beat it by adjusting the angle, pull distance, or rubber band tension. 🎯

Have fun!

• 🎯 Set up targets (cups, hoops, zones) and score points for landing in each one.
• 📏 Keep a score sheet and record your best distance after each tweak.
• ⚙️ Try different arm lengths — does a longer arm throw farther?
• 🏆 Challenge another person to build their own and compete for distance.

Why It’s Amazing

• Physics: Children directly experience potential and kinetic energy — pull back creates stored energy, release converts it to motion. 🔋
• Engineering Design: Build, test, measure, adjust — this is the real engineering loop. Every tweak is an experiment with a result. ⚙️
• Measurement: Comparing distances with a ruler and recording results introduces systematic data collection in a fun context. 📏
• Resilience: When the catapult misfires or launches sideways, that is a data point — not a failure — and figuring out why builds persistence. 💪

Pro Tips

For ages 6–8: Simplify the build — just tape the spoon directly to a single straw and loop a rubber band at the midpoint. Focus on the fun of launching, not precision engineering.

For ages 8–11: Introduce the challenge of a specific target distance. Measure and record three launches, compute the average, and adjust the design to improve it.

For ages 11+: Add multiple rubber bands and measure how tension affects distance. Graph launch distance vs. pull angle for a genuine science experiment. 📊