## Overview

Students are introduced to the idea of designing and making a car that uses a balloon as its energy source. They are challenged to think about how a balloon car would be similar to a wind-up and how it would be different. Next,  they create concept drawings and materials lists for their balloon cars.  Finally, they begin their balloon cars.

• Photo copy the worksheet: “My Balloon Car”.
• Balloon for demonstration, procedure step 1.

## Materials

• For each student, 4 wheels, 2 wooden skewers (axles), 4 ¼”  x 5 ½” cardboard rectangle, 2 straws (¼” and 5/16” diameters), a foam block, 1 balloon, 1 storage bag;
• For each group, masking tape, rubber bands, and a balloon pump.

## Procedure

1. Class meeting. Show the class a balloon. Blow it up and then release it. Ask:

• When I blow this up, what changes do you see?
• How is this different from stretching a rubber band? How is it similar? Emphasize that each stores potential energy as elastic energy.
• How is the balloon’s energy changing as I blow it up?
• Where is the energy coming from to make the balloon’s energy change?
• Where do I get the energy to blow it up?
• Where does the energy of the balloon go when I release it?

Ask students to think about how they could use a balloon to make something similar to a wind-up:

• Earlier, we made wind-ups. What made them go?
• How could you make a car that uses a balloon as its energy source?
• What materials would you need?

2. Planning a balloon car:   Planning a balloon car: Introduce the materials for the car: spin a wheel on a skewer (axle); name the cardboard the "car body".  Tape the large straw to the balloon and blow the balloon up with the air pump and identify the masking tape and rubber bands as ways to hold everything together. Distribute the Worksheet "My Balloon Car" for students' initial planning. Give students materials only after they have an initial plan.

3. Starting to make balloon cars:    Provide each student with 4 wheels, 2 skewers and a cardboard rectangle. Give tape and rubber bands to each group. The first task is this:

Make a car that rolls easily and straight.

Here are two videos. The first shows a variety of car bodies. The second shows how to make a basic car.  Allow students to experiment with the materials, and record any problems that come up. Here are videos of some typical issues and possible fixes:

When students have a car that rolls easily and straight, provide a large and small straw and a balloon to each student and a balloon pump to the group. They procede to find ways to make a balloon car.

SAFETY NOTE: To avoid spreading infections, do not allow students to blow balloons up by mouth. Each student should always use a balloon pump to blow up a balloon.

4. Outcomes:

• Students review their work with wind-ups, by considering a related, but different problem.
• Student apply the concepts of potential and kinetic energy, and energy conservation, in a context similar to wind-ups.
• Students try to imagine a new design without the benefit of a sample.