Rubber Band Car Challenge for Grades 3-5

Background Information for Teachers

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

You can use rubber band-powered cars, like the ones in Figure 1, to explore many different science and engineering concepts with your students. In general, these cars consist of wheels and axles mounted on a frame. A rubber band is connected to an axle on one end and the frame on its other end. Twisting the axle stretches and winds up the rubber band. When you release the axle, the rubber band contracts, spinning the axle and propelling the car forward.

The concepts you decide to focus on will depend on your classroom and curricular needs, but here are some suggestions:

• Explore simple machines, such as the wheel and axle, which are a key part of each car.
• Talk about forces, like weight and friction, and how they affect the car's motion.
• Discuss energy storage and transformation. The stretched rubber band stores elastic potential energy, which is converted to kinetic energy as the rubber band contracts and the car moves forward.
• Use the engineering design process to help students iteratively design, build, and test their cars to improve their performance.
• Analyze the different material properties of the materials available for building the cars. Discuss how some materials are better for certain purposes than others.

Additional Background Links

• The Engineering Design Process, Science Buddies.

Prep Work (15 minutes)

• Gather all the construction materials in a central location for students.
• Print the student worksheets and scoring worksheets (one of each for each student).
• Optional: assign the introductory video for your students to watch before class.
• Set up testing areas for students. Students will need open floor space free from furniture and obstructions to test their cars. Mark an official start line on the floor using tape.

Engage (15 minutes)

Introduce the challenge to your students. Explain that their main goal is to build a rubber band-powered car that can go as far as possible. Show your students the introductory video if they have not watched it already. Then, go over the student worksheet and the contest rules (also included in the student worksheet):

Explore (1-2 hours)

1. Design. Before they start building anything, have each student draw two ideas for a rubber band car on their worksheet. Remind them to think about the materials they are allowed to use, and how they can use those materials to build.
2. Compare. After drawing two designs, have each student work independently to compare their first and second design, and think about which design would work better for the challenge.
3. Share. Have students form groups and share their designs with other students in their group. Each group should decide on a single design to build. Their final design can include a combination of ideas from multiple students.
4. Build. After agreeing on a single design to build, students should start building it. They may need to make changes or adjustments as they build. This is OK.
5. Test. Students might want to test their car in stages as they build. For example, first they can make sure the axles spin smoothly by hand. Then they can make sure the entire car rolls when pushed. Finally, they can try twisting up and releasing the rubber band. They should make observations about what works (or does not work) while testing, and think about how they can improve their design.
6. Improve. Based on their observations, students should try to improve their design and, if possible, make their car go farther.
7. Re-test. After making improvements, students should re-test their cars. Emphasize that it is OK if the car does not work on the first try (or second, or third...)! This is why engineers test things, so they fix them and make improvements. Allow your students to continue improving and re-testing their cars as time allows.

Troubleshooting Tips: there are a few common issues you might encounter, especially with younger students. Here are some tips to help them succeed:

• Trouble winding up the rubber band: note that the rules say that up to two people can twist the rubber band. It may be easiest for one student to hold the car (using two hands) while another student twists the axle.
• Car does not go straight: note that this is OK, since you will just measure the distance from the start location to wherever the car stops. Cars do not have to go straight. If a car is curving severely off to one side, make sure the wheels and axles are aligned with each other.
• Car does not move at all: make sure that the axles are not jammed. If you pick the car up, the axles should be able to spin freely if you spin them by hand.
• The wheels spin but just slip on the ground, and the car does not move forward: this can be counterintuitive, but if you wind the rubber band too tightly, the wheels might spin so fast that they just slip on the ground because there is not enough friction. You can try different methods to increase friction, such as adding more weight to the car or adding rubber bands as "tires" for the wheels. You can also use a thinner rubber band or not wind the rubber band as tightly.
• See the Engineering Challenge 2024 Rubber Band Car FAQ for additional questions.

Optional: note that students can also improve their scores by using fewer materials. For advanced students, you can encourage them to try to "slim down" their cars, for example, by using three wheels instead of four, or using fewer materials to build the frame.

Reflect (30 minutes)

Once all groups have finished building their devices, have a class-wide competition to calculate official scores.

1. Make sure each group has counted the total quantity of each material used in their final car. Materials used in earlier prototypes do not count. Record these quantities in the scoring worksheet.
2. If you have not already, make a start line on the floor with tape. Mark a spot on the start line using a marker or a second smaller piece of tape.
3. One at a time, let two students from a group wind up their car's rubber band, place it on the floor completely behind the start line and centered behind the mark, and let the car go. Watch the car and make sure no one touches it, it does not crash into anything, and it comes to a complete stop on its own.
4. Use a tape measure to measure the distance from the point on the start line to the nearest point on the car.
5. If time allows, let students keep testing to see if they can get a longer distance.
6. Each group should record the farthest distance their car traveled and then calculate their score using the scoring worksheet. An example calculation is provided below for your reference.

Scoring

Your score is calculated using this equation:

Equation 1:   $\: Score\; = \left(2\times distance \;in\; centimeters\right) - \left(total\;materials \;points\right)$

A scoring worksheet and scoring spreadsheet are available to help you calculate your score. You can also read the following written instructions or watch the video with an example calculation.

1. If you measured your distance in inches, convert it to centimeters by multiplying by 2.54. For example, if your car traveled 10 inches, that is 10×2.54 = 25.4 cm.
2. Count the total number of each material item that you used. Material quantities are not prorated. For example, even if you only use one quarter of a 12×12 inch sheet of cardboard, you must count the entire sheet (so you would enter "1" for the quantity in the scoring worksheet, not "1/4" or "0.25."). If you use any tape at all, you must enter "1" for tape.
3. For each material, multiply the quantity by the point cost for that material to calculate the subtotal for that material. For example, if you used 4 CDs, which are worth 2 points each, that is 4×2=8 points.
4. Add up all of the subtotals to get your total material points cost. For example, a car that used all of the following materials would have a total point cost of 31.
   1. 4 CDs (4×2 points each = 8 points)
   2. 1 sheet of cardboard (1×10 points each = 10 points)
   3. 2 pencils (2×1 point each = 2 points)
   4. 2 straws (2×1 point each = 2 points)
   5. 1 sheet of paper (1×1 point each = 1 point)
   6. 1 rubber band (1×2 points each = 2 points)
   7. 1 paper clip (1×1 point each = 1 point)
   8. 1 roll of tape (1×5 points = 5 points)
5. Plug your distance in centimeters and total material points cost into Equation 1 to calculate your score. For the car in the example above, with a distance of 25.4 cm and a material points cost of 31, the score is (2×25.4)-31 = 19.8.
6. Round your final score to the nearest whole number. The score of 19.8 would round up to 20. If the score was 19.49, that would round down to a final score of 19. The score submission form will not accept decimals.

Discuss the results of the competition as a class.

• Did any students draw designs that looked the same?
• Did anyone draw a design that no one else thought of?
• What problems did groups encounter during the building/testing process?
• Did the best designs have anything in common?

Assess

• Collect your students' worksheets and use them to assess how they worked through the design process.
• Ask each group to tell the rest of the class about their design. Why did they choose their design? Did they have any problems when building it?

Lesson Plan Variations

Did your students enjoy this type of hands-on project? Check out the other Engineering Challenges and try them in your classroom!