Popsicle Stick Catapult

Grade Level: 3-6
Time: 45-60 minutes
Group Size: 2-3 students per team

Materials Needed (per team):

• 15-20 popsicle sticks
• 5-7 rubber bands (various sizes)
• 1 plastic spoon (for the launch arm)
• Mini marshmallows (as projectiles, 1 bag shared across class)
• Tape (masking or duct)
• Scissors
• Ruler or measuring tape
• Target rings taped on the floor (optional, for accuracy round)

The Challenge:

Build a catapult that launches a mini marshmallow as far as possible. Once distance is measured, a second round tests accuracy: can you hit a target from 3 feet away?

How Catapults Work:

A catapult is a lever: a rigid arm that pivots around a fulcrum. When you push one end down and release it, the other end swings up fast, launching whatever is sitting in the cup. The tension in the rubber bands stores energy; release is the trigger.

Key lever parts:

• Arm: The popsicle stick or spoon that swings
• Fulcrum: The pivot point (the stack of sticks the arm rests on)
• Cup: The spoon bowl that holds the projectile
• Spring: Rubber bands that pull the arm forward when released

Step-by-Step Instructions:

Setup (5 minutes):

1. Mark a launch line on the floor
2. Clear a 15-foot path ahead for distance testing
3. For accuracy round: tape three concentric rings on the floor (at 2, 3, and 4 feet from the launch line)

Building Phase (30-35 minutes):

Basic catapult design (recommended starting point):

Step 1: Build the base

1. Stack 8-10 popsicle sticks flat and wrap rubber bands around both ends tightly to hold them together
2. This is the base and gives the catapult stability and weight

Step 2: Build the fulcrum

1. Stack 4-6 popsicle sticks and wrap them together with a rubber band
2. This smaller stack will sit on top of the base and act as the pivot point

Step 3: Create the arm

1. Lay 1-2 popsicle sticks end-to-end to make the launch arm
2. Tape the plastic spoon to the long end of the arm (the launch end)
3. The spoon bowl should face up and point away from the base

Step 4: Assemble

1. Place the fulcrum stack on top of the base, near one end (not the center)
2. Lay the arm across the fulcrum so the spoon end is the long side
3. Wrap a rubber band around the arm and base to hold them together at the fulcrum point — tight enough to hold shape but loose enough to allow the arm to swing
4. Add a rubber band from the short end of the arm down to the base as the spring — this is what launches the projectile

Step 5: Test launch

1. Push the spoon arm down toward the base
2. Place a marshmallow in the spoon
3. Release and observe trajectory

Adjustments to teach:

• Too weak: Add a second rubber band to the spring
• Arm won’t stay in place: Tighten the fulcrum rubber band
• Marshmallow goes straight up: Move the fulcrum point toward the center — the arm is too short on the launch side
• Marshmallow rolls out of the spoon: Launch faster or tilt the spoon slightly inward

Teacher Tips:

• Demonstrate the basic design before building time — catapult mechanics are not intuitive to all students
• The most common failure is a base that is too light and tips over on launch — extra sticks in the base fix this
• Encourage students to test early and often, not just at the end
• Mini marshmallows are safe projectiles and soften the mess concern; have a clear no-eating rule before the challenge begins

Testing Phase (10-15 minutes):

Round 1: Distance

1. Each team gets 3 launches from behind the line
2. Mark where the marshmallow first lands
3. Record best distance

Round 2: Accuracy

1. Set a target ring 3 feet away
2. Each team gets 3 attempts
3. Score: 3 points for center ring, 2 for middle, 1 for outer ring

Learning Objectives:

• Levers: Arm, fulcrum, load — how position of fulcrum changes force and distance
• Stored energy: Stretched rubber bands as springs
• Projectile motion: Launch angle affects both height and distance
• Iteration: Adjusting fulcrum position and spring tension changes results

Differentiation:

• Easier (Grade 3): Provide a pre-assembled base; students only build and attach the arm
• Harder (Grades 5-6): Challenge teams to hit a specific distance target (not just as far as possible); they must calculate and adjust rather than just maximize power
• Extension: Move the fulcrum position and record how it changes launch distance; graph results to see the relationship

Discussion Questions:

• Where is the fulcrum in your catapult? What happened when you changed its position?
• Why does the shorter side of the arm need the spring?
• A heavier base helps the catapult not tip — why does that matter for launch distance?
• Where do levers show up in everyday tools? (seesaws, bottle openers, scissors, wheelbarrows)

Common Problems and Solutions:

Real-World Connections:

• Medieval siege catapults used the same lever principle — long arm, short arm, heavy counterweight
• Trebuchets replaced catapults because a swinging counterweight on the short end released energy more efficiently
• A seesaw is a lever with the fulcrum in the center; moving it changes who goes up or down more easily
• Spoons, nail clippers, and broom handles all use lever mechanics