Rubber Band Racer

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

Materials Needed (per team):

• 1 piece of corrugated cardboard (about 6” x 10”, cereal box or similar)
• 2 rubber bands (same size, standard medium bands work well)
• 4 bottle caps, cardboard circles, or wooden wheels
• 2 wooden skewers or bamboo sticks (for axles)
• 2 short straws (to hold axles in place)
• Tape (masking tape preferred)
• Scissors
• 1 small binder clip or wooden spool (for the wind mechanism)
• Ruler or measuring tape
• Tape for marking the start line

The Challenge:

Build a car powered only by a wound rubber band. The car that travels the farthest in a straight line wins.

How Rubber Band Racers Work:

A rubber band stores energy when you wind it up (elastic potential energy). When you release it, that stored energy turns into motion (kinetic energy). The axle unwinds the rubber band, spinning the wheels and pushing the car forward.

The simplest version: Wrap a rubber band around the rear axle several times. When released, the axle unwinds, spinning the wheels.

Step-by-Step Instructions:

Setup (5 minutes):

1. Mark a start line on the floor with tape
2. Clear a straight path at least 10 feet long (a hallway works best)
3. Demonstrate winding and releasing a rubber band around a pencil so students understand the basic energy transfer

Planning Phase (10 minutes):

Before building, teams sketch their design:

• Where will the axles go?
• How will the rubber band connect to the axle?
• How many winds do they think will give the most power without snapping?

Key teaching point: “This is the same energy your arm puts in when you wind something up. The tighter you wind it, the more energy is stored, but there’s a limit before it breaks or spins out.”

Building Phase (30-35 minutes):

Step 1: Build the car body

1. Cut cardboard into a rectangle roughly 4” x 8”
2. Fold or double the cardboard for extra rigidity if needed

Step 2: Make the axle holders

1. Cut two straws to the width of the car body
2. Tape one straw near the front of the car (underside) and one near the back
3. The straws should be parallel and level with the floor
4. Make sure the straws are taped firmly but the skewers can spin freely inside them

Step 3: Make the wheels

1. Push a skewer through each straw
2. Attach wheels to both ends of each skewer (bottle caps, cardboard circles, or wooden wheels)
3. Secure wheels with tape or clay so they stay on but the skewer can still spin

Step 4: Add the rubber band drive

1. Hook one end of the rubber band around the rear axle (skewer)
2. Stretch the rubber band forward and hook the other end around the front axle or a fixed point on the body
3. OR: Wrap the rubber band around the rear axle 3-4 times so it unwinds and spins the wheels

The winding method (recommended for Grades 3-6):

1. Hold the car body still
2. Roll the car backward to wind the rubber band around the rear axle
3. The more you roll it back, the more winds, the more stored energy
4. Release and watch it go

Teacher Tips:

• Wheels that do not spin freely are the most common reason cars barely move — check axles before testing
• Wheel alignment matters: if one wheel drags, the car curves
• Challenge students to find the right number of winds — too few and it barely moves, too many and the rubber band snaps or the wheels spin in place
• Lighter cars travel farther — encourage minimal tape

Testing Phase (10-15 minutes):

1. Each team gets 3 runs from the start line
2. Mark the landing point for each run
3. Measure the best distance
4. Allow quick adjustments between runs

Tiebreaker: If two cars travel nearly the same distance, run them side-by-side and see which travels farther in a single race.

Learning Objectives:

• Elastic potential energy: Energy stored in a stretched or wound rubber band
• Kinetic energy: Energy of motion released when the rubber band unwinds
• Friction: How it affects whether wheels roll or slip
• Wheel mechanics: Axle alignment, wheel size, and rolling resistance
• Iteration: Tuning wind count and wheel alignment for maximum distance

Differentiation:

• Easier (Grades 2-3): Use pre-cut cardboard and pre-punched wheels; focus on wheel attachment and basic winding
• Harder (Grades 5-6): Limit to 1 rubber band; add a steering challenge (car must hit a target or pass through cones)
• Extension: Test whether larger wheels travel farther than smaller ones with the same number of winds; graph results

Discussion Questions:

• Where did the energy in your car come from?
• How many winds gave the best result? Why do you think that is?
• What happened if you wound it too tight?
• Why do wheels that rub against the cardboard body make the car go shorter distances?

Common Problems and Solutions:

Real-World Connections:

• Wind-up toys use the same principle: stored elastic energy released as motion
• Springs in clocks and watches store and release energy the same way
• Muscle energy in your legs is similar: your muscles store chemical energy and release it as movement