Balloon-Powered Car

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

Materials Needed (per team):

• 1 piece of cardboard (about 6” x 8”, from cereal box or similar)
• 2-3 balloons (standard size)
• 4 bottle caps OR cardboard circles for wheels
• 2 straws (straight, not bendy)
• 2 wooden skewers or straight sticks for axles
• Tape (masking or duct tape works best)
• Scissors
• Optional: hot glue gun (teacher supervised)

The Challenge:

Design and build a car that uses ONLY the air from a balloon to propel itself forward. The car that travels the farthest in a straight line wins!

Step-by-Step Instructions:

Setup (5 minutes):

1. Mark a starting line with tape on the floor
2. Clear a long, straight pathway (hallway is ideal)
3. Distribute materials
4. Show students how balloon propulsion works: blow up a balloon, let it go - the air pushes it forward!

Building Phase (35-40 minutes):

Step 1: Build the Car Body (10 minutes)

1. Cut cardboard into a rectangle (about 4” x 6”)
2. This is your car’s base
3. Make sure it’s sturdy - fold edges if needed for strength

Step 2: Make the Wheels (10 minutes)

1. Option A - Bottle Caps:
   • Poke a small hole in the center of each cap using a skewer
   • The hole should be just big enough for the skewer to spin freely
2. Option B - Cardboard Wheels:
   • Cut 4 circles from cardboard (about 2-3 inches diameter)
   • Poke holes in the centers
   • Make them as round as possible for smooth rolling

Step 3: Attach the Axles (10 minutes)

1. Cut two straws to the width of your car base
2. Thread a skewer through each straw
3. Tape the straws to the UNDERSIDE of the car base (one near front, one near back)
4. The straws should be taped down, but the skewers should spin freely inside
5. Push wheels onto the ends of the skewers
6. Secure wheels with tape or clay so they don’t fall off
7. TEST: Does your car roll smoothly? If not, adjust!

Step 4: Add the Balloon Power (10 minutes)

1. Cut a straw in half
2. Insert the straw into the neck of the balloon
3. Tape around the balloon neck to seal it to the straw (must be airtight!)
4. Tape the straw/balloon to the TOP of the car, pointing backward
5. The balloon should sit on top of the car with the straw pointing toward the back

Final Setup:

• Blow up the balloon through the straw
• Pinch the straw to keep air in
• Place car at starting line
• Release and watch it go!

Teacher Tips:

• The seal between balloon and straw is CRITICAL - if air leaks, it won’t work
• Demonstrate how to blow up the balloon while it’s attached to the car
• Lighter cars go farther - don’t use too much tape!
• Wheels must spin freely - this is the #1 problem area

Testing Phase (10-15 minutes):

1. Each team gets 3 test runs
2. Mark where each car stops
3. Measure distance from starting line
4. Best distance counts
5. Allow quick adjustments between runs

Learning Objectives:

• Newton’s Third Law: For every action (air pushing backward), there’s an equal and opposite reaction (car moves forward)
• Engineering design: Wheels, axles, and propulsion systems
• Aerodynamics: Does car shape affect distance?
• Problem-solving: Troubleshooting mechanical issues

Differentiation:

• Easier: Provide pre-made wheels; allow use of hot glue for stronger connections
• Harder: Require cars to travel a specific path (through cones); add weight restrictions
• Extension: Test on different surfaces (carpet vs. tile); experiment with balloon sizes

Troubleshooting Guide:

Discussion Questions:

• What happened to the air inside the balloon when you let go?
• Why did the car move forward when air went backward?
• Which design traveled farthest? What made it successful?
• How could you make your car go even farther?

Real-World Connections:

• Rocket ships use the same principle (thrust pushing backward makes rocket go forward)
• Jet engines work similarly
• Balloons are like stored energy - potential energy becomes kinetic energy