Balloon-Powered Car (4th-5th)

Materials:
A balloon
Rubber bands
Cardboard
3 straws
2 wooden skewers
Scissors

Steps:
Build the Car Body: Cut a small rectangle of cardboard
Make the Wheels: Cut 4 small identical circles of cardboard and poke small holes in them
Create the Axles: Poke each skewer into a short piece of straw and slide them into the cardboard circles. The wheels should be able to spin now.
Attach Axles to the Car: Tape the straws to the bottom of the car body.
Attach the Balloon Nozzle: Slide the balloon over one end of a straw and secure it with a rubber band.
Mount the Balloon System: Tape the straw pointing backward on top of the car. The balloon should sit on top, with the open straw end hanging off the back.
Test It! Blow up the balloon through the straw. Pinch the straw closed, place the car on the floor, and release.

Key Concepts:
Action–reaction (Newton’s 3rd Law): Air pushes backward, car moves forward
Friction: Wheels rubbing slow the car down
Engineering design: Test → fix → try again