# Balloon Car

6th-8th
Group Size
2-4 students
Active Time
1 hour
Total Time
1 hour
Area of Science
Mechanical Engineering
Key Concepts
Engineering design, potential energy, kinetic energy, conservation of energy
Learning Objectives
• Understand what potential and kinetic energy are and how one can be converted to the other.
• Use the engineering design process to iteratively test and modify a design.

## Overview

Your students will design, build, and race balloon-powered cars in this fun lesson plan that teaches about engineering design and kinetic and potential energy.

## NGSS Alignment

This lesson helps students prepare for these Next Generation Science Standards Performance Expectations:
• MS-PS3-5. Construct, use, and present arguments to support the claim that when the kinetic energy of an object changes, energy is transferred to or from that object.
• MS-ETS1-4. Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved.
This lesson focuses on these aspects of NGSS Three Dimensional Learning:

 Science & Engineering Practices Disciplinary Core Ideas Crosscutting Concepts Constructing Explanations and Designing Solutions. Apply scientific ideas or principles to design, construct, and test a design of an object, tool, process, or system. Engaging in Argument from Evidence. Evaluate competing design solutions based on jointly developed and agreed-upon design criteria. PS3.A: Definitions of Energy. Motion energy is properly called kinetic energy; it is proportional to the mass of the moving object and grows with the square of its speed. A system of objects may also contain stored (potential) energy, depending on their relative positions. PS3.B: Conservation of Energy and Energy Transfer. When the motion energy of an object changes, there is inevitably some other change in energy at the same time. ETS1.B: Developing Possible Solutions. A solution needs to be tested, and then modified on the basis of the test results in order to improve it. Energy and Matter. Energy may take different forms (e.g. energy in fields, thermal energy, energy of motion) The transfer of energy can be tracked as energy flows through a designed or natural system.

## Credits

Ben Finio, PhD, Science Buddies

This lesson plan is related to the 2015 Fluor Engineering Challenge.

## Materials

Note: since this is an engineering design project, it does not have an exact list of required materials for students to build their cars. You can use the materials you have available in your classroom, including recycled materials, to keep costs down. The list below provides some suggestions.

• Open floor space
• Tape measure
• Wheels (round objects like CDs and bottle caps, etc.)
• Axles (wooden skewers, pencils, straws, etc.)
• Frame/body (plastic bottles, cardboard boxes, popsicle sticks, etc.)
• Straws
• Balloons
• Rubber bands
• Tape
• Scissors
• Other assorted classroom/office supplies (paper clips, binder clips, zip ties, etc.)

## Background Information for Teachers

This section contains a quick review for teachers of the science and concepts covered in this lesson.

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.

Figure 1. Examples of two balloon-powered cars built with different materials.

## 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.

## 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.
Troubleshooting

Your students might encounter some problems when building their cars. Remember that overcoming these challenges is part of the engineering design process. However, here are some common problems and hints you can give your students if they get stuck.

Car does not move at all
• Try inflating the balloon more. Pre-stretch the balloon by hand to make it easier to inflate.
• Make sure there is not too much friction on the axles. If you pick the car up, you should be able to spin the wheels freely.
• Try making the car lighter.
Car's motion is jerky and not smooth
• Make sure the wheels are centered on the axles. Off-center wheels will wobble as they roll.
• Make sure the wheels can rotate smoothly. Try spinning each wheel by hand. Is the wheel harder to spin at any point during the rotation? Is anything on the axle causing it to get stuck?
Car drifts off to one side
• Make sure the car's wheels are symmetric and aligned.
• Make sure the straw is centered on the car's body and pointed directly backwards.
Air leaks out of the balloon
• Wrap the rubber band or tape more tightly around the neck of the balloon to help seal any leaks.
• Make sure you pinch the tip of the straw firmly with your finger to prevent air from leaking out the end of the straw.
• Wait until you get to the testing area to inflate the balloon, and test the car very quickly before air has too much time to leak out.

## 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:

## 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   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.
• CAD Technician   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.

## 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.

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6th-8th
Group Size
2-4 students
Active Time
1 hour
Total Time
1 hour
Area of Science
Mechanical Engineering
Key Concepts
Engineering design, potential energy, kinetic energy, conservation of energy
Learning Objectives
• Understand what potential and kinetic energy are and how one can be converted to the other.
• Use the engineering design process to iteratively test and modify a design.

Class Materials