Balloon Car Lesson Plan

Background Information for Teachers

In this project, your students will design and build balloon-powered cars. The cars are propelled forward by air escaping from a balloon, and can be built using a variety of different materials as shown in Figure 1.

Image Credit: Science Buddies
Figure 1. Examples of two balloon-powered cars built with different materials.

Regardless of the materials used to build them, the basic operating principle of the cars is the same. When you inflate a balloon, it stores potential energy in the stretched rubber of the balloon and the compressed air inside it. When you release the balloon, air escapes out the nozzle, pushing the balloon forward (Figure 2). The stored potential energy is converted to kinetic energy, the energy of motion, as the balloon is propelled forward. According to conservation of energy, the amount of stored potential energy equals the resulting amount of kinetic energy. Eventually, the kinetic energy is converted to thermal energy (or heat) as friction slows the balloon down. The air escaping the balloon also demonstrates Newton's third law of motion: for every reaction there is an equal and opposite reaction.

Image Credit: Ben Finio, Science Buddies / Science Buddies
Figure 2. Newton's third law of motion for an inflated balloon.

When you inflate a balloon and release it, it will tend to wobble and zoom randomly around the room. You can attach the neck of a balloon to a straw by wrapping a rubber band or tape around it several times, as shown in Figure 3. When you connect the straw to the body of a car, this allows you to aim the direction of the escaping air, so you can make sure it pushes the car forward. The car will initially accelerate as the balloon deflates, and eventually it will come to a stop as the balloon runs out of air and friction slows the car down.

Image Credit: Ben Finio, Science Buddies / Science Buddies
Figure 3. Balloon attached to straw with rubber band.

In this lesson, your students will follow the engineering design process. You will help them get started by showing them how to connect a balloon to a straw as shown in Figure 3, but then they will select their own materials to design and build the body, wheels, and axles of their cars. The engineering design process is an iterative process where students design, build, and test their cars. It is important for students to understand that there is no single "right answer" to an engineering project. There are multiple possible solutions to the problem, and it is OK if their cars do not work very well on the first try. Part of the process is redesigning, rebuilding, and retesting your container based on what you learn from your initial tests.

Additional Background Links

• Energy of Motion, Physics4Kids
• Potential Energy, the Physics Classroom
• Kinetic Energy, the Physics Classroom
• Engineering Design Process, Science Buddies

Prep Work (5 minutes)

• If necessary, rearrange furniture in your classroom so students have a large area of open floor space to test their cars.
• Set up a tape measure on the floor so students can measure how far their cars travel.

Engage (5 minutes)

1. Blow up a balloon and pinch the nozzle shut.

   What type of energy is stored in the balloon?

   The inflated balloon stores potential energy in the form of the stretched rubber of the balloon and the compressed air inside the balloon. The more the balloon is inflated, the more potential energy it stores.

2. Release the nozzle and let the balloon fly around the room.

   What type of energy is the potential energy converted to?

   The balloon's stored potential energy is converted to kinetic energy, the energy of motion. An object's kinetic energy depends on its mass and the square of its velocity. For example, if two objects are moving at the same speed, the heavier one has more kinetic energy.

   What happens to the balloon's kinetic energy? Why doesn't the balloon keep moving forever?

   This balloon's kinetic energy is gradually converted to thermal energy as friction slows it down. The balloon may also collide with an object like a wall or desk, which exerts a force to stop the balloon (and converts the remaining energy into thermal energy).

   The balloon zoomed randomly around the room. How could we better control the direction of the air escaping from the balloon?

   Demonstrate how you can attach the neck of the balloon to a straw using a rubber band or tape, as shown in Figure 3 of the background section. Inflate the balloon through the straw and release it.

3. Explain that the students will use materials you have available in the classroom to build balloon-powered cars. Their cars will need a body, wheels, and axles, and will be propelled forward by air escaping from a balloon.

   What materials could you use for the body of your car?

   Examples include plastic bottles, cardboard boxes, or glued-together popsicle sticks.

   What materials could you use to build a wheel and axle?

   One method includes threading a wooden skewer through a straw, and punching both ends of the skewer through plastic bottle caps (see Figure 1, right side, in the background section). You could do something similar with a pencil, piece of paper rolled into a tight tube, and CDs. Can your students think of other ideas?

4. The goal is to see who can build a car that travels the farthest before coming to a stop. They will follow the engineering design process to design, build, and test their cars. This means they do not have to get their car "right" on the first try. They will be allowed to test and redesign their cars (as much as possible while time allows) before a final class competition.

https://www.youtube.com/watch?v=jr3BOE_EpOk

Explore (50 minutes)

Important: for sanitary reasons, designate one student from each group to inflate their car's balloon, so students are not sharing straws.

1. Have each group use the student worksheet to design their car before they start building.
2. Let students gather materials and start building their cars.
3. When individual groups are ready, they can come to the open floor space to test their car. To test a car:
   1. Blow through the straw to inflate the balloon.
   2. Quickly put your finger over the tip of the straw to seal the air inside.
   3. Place the car on the floor at the "0" mark on the tape measure.
   4. Release your finger and watch the car until it comes to a stop.
   5. Record how far the car traveled using the data table in the student worksheet.
4. Encourage students to ask questions like these when they test:

   Does the car move in a straight line, or does it curve to one side?

   Does the car move forward smoothly, or is its motion jerky?

   Does the car continue to coast after the balloon is deflated, or does it abruptly come to a stop?

   If they notice any problems, how could they improve the design?

5. Prompt students to think about flow of energy as they test their cars.

   How can you increase the amount of potential energy stored in your system? Could this create any problems or challenges?

   You can increase the amount of stored potential energy by inflating the balloon more. However, if you inflate the balloon too much, it might pop or fly off the straw. Some students may also think of adding a second balloon; this would also increase the stored potential energy.

   For a fixed amount of initial potential energy (the balloon is inflated a certain amount), how can you maximize the distance your car travels?

   Possibilities include making the car lighter, and minimizing the amount of energy lost to friction by making the axles spin more smoothly.

6. Allow students to return to their work areas to modify, improve, and retest their cars.
7. With about 15 minutes remaining (depending on the number of groups), organize a class-wide competition to see whose car travels the farthest. You can give each group three attempts, and either record their farthest distance or calculate the average distance.

Reflect (5 minutes)

Discuss the following questions as a class.

What problems did students encounter when designing and building their cars? How did they overcome these challenges?

Did the most successful designs have anything in common, like materials or construction methods?

If students had more time, how would they further modify or improve their designs? Would they use any materials not currently available in the classroom?

The cars in this project store potential energy in inflated balloons. How do real cars store energy? How is this energy converted to kinetic energy?

Real cars store chemical energy in gasoline tanks or electric batteries, which power engines to spin the car's wheels, converting the stored energy to kinetic energy.

Assess

Use this quiz to assess student learning after the activity; quiz is available in online and pdf formats:

• Online quiz, assignable in any LMS
• Quiz (pdf) and answer key (pdf)

Make Career Connections

Discussing or reading about these careers can help students make important connections between the in-class lesson and STEM job opportunities in the real world.

Automotive Engineer

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Career Profile

Real cars are complicated machines with many different sub-systems inside them, ranging from passenger safety features like seatbelts and airbags, to comfort features like the heating and air conditioning systems, and of course the engine and all the parts that make the car move! Automotive engineers are involved in designing all the different parts that go into building a complete car. Read more

CAD Technician

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Career Profile

In this project you drew a sketch of your design before you started building your car. Computer Aided Design (CAD) technicians create computer drawings and three-dimensional models of cars during the design process and when the final designs are sent off to the factory for manufacturing. Read more

Lesson Plan Variations

• Devise a scoring system to assess the cars' performance. For example, in addition to measuring distance, you can:
  • Give each team a limited budget and assign a "cost" to each construction material.
  • Weigh each car and reward cars that are lighter weight.
  • Measure how much additional weight the cars can carry a certain distance (like pennies).
• Build balloon-powered rockets instead of cars in the Two-Stage Balloon Rocket Lesson Plan. These projects can also be used to teach about Newton's laws of motion in addition to kinetic and potential energy.