A: Most definitely! Let’s design and build something, and then we’ll use it to explore some science. But first, let’s take a quick look at the difference between science and engineering. Scientists try to understand how things work in the universe and why things are the way they are. Why is the sky blue? What are stars? How do birds fly? Engineers try to solve real-world problems. How can I build a bridge strong enough to support cars and trucks? How can I make a wireless phone? How can I make a more powerful microscope? To answer questions like these, the engineer needs to use a lot of science.
Here’s an engineering question or problem or challenge: Can we build a car that will move (at least a little bit) by itself, without being pushed? To answer this question— or any engineering question—we need to start with some science. Ask: If your toy car is going to start moving, what does it need to have? Depending on the grade level, you might get different answers for this question, like a push or a pull, a force, or, at the higher levels, energy. If you’ve done lessons on force and motion, then students should know that starting something moving requires a force. And if you’ve discussed energy, you can remind students that getting something moving is going to require some energy.
So, if we need a force—a push or a pull—what’s going to provide that force? If you’re riding a bicycle or tricycle, that force comes from your muscles, as your legs push on the pedals. In a car, that force comes from the engine. But we can’t have an engine in our little toy car, so we need something else to provide the force. Maybe students will have some other ideas, but let’s say that we’re going to use a rubber band.
A rubber band can work because when it’s stretched, it pulls back, exerting a force. And when the rubber band is stretched, it has stored energy. As the rubber band unwinds and becomes less stretched, that stored energy gets transferred to the car, now in the form of energy of motion, or kinetic energy.
Get students’ ideas for how a rubber band might be used to make a toy car move. Some students might think of a slingshot kind of arrangement, but let’s try for a more elegant engineering solution—one that allows the energy stored in the rubber band to be released more gradually. The idea is to design the car so that the rubber band gets wound up and gradually unwinds as the car moves. The design of such a car is an example of engineering. (See “What is Engineering.”)
There are many websites with instructions for making this kind of car, so I don’t think I need to repeat the instructions here. You’ll find links to some of them in the Internet Resources at the end of this article. Depending on your students’ abilities, they can construct a car of their own design or use the design from one of the websites with its step-by-step instructions.
Emphasize that the rubber band– powered car doesn’t have to actually look like a car. It just needs to be something that rolls along by itself due to the pulling or unwinding of a rubber band. The last three designs shown in the Internet Resources look nothing like a car and are among the simplest designs. The last one requires only a spool of thread, two paper clips, a rubber band, and a clothespin (or small stick like a short pencil). Perhaps the students’ cars will look like one of those in Figure 1. For some of the online designs, some adult assistance will be needed, for example, if a hot glue gun is needed. Sometimes the wheels need more traction, which you can obtain by wrapping some additional rubber bands around the wheels. Also note that if you have only short rubber bands, you can make a longer one by connecting two or more of them as shown in Figure 2.
It takes some science to design a rubber band–powered car, and once students have their cars, they can use them to investigate more science! Students can have races to see whose car is fastest, but be sure to have a good discussion about what made it fast. Besides the fastest car, you can have a contest to see whose car travels the longest distance. What made it possible for that car to travel so far? Did it have a big rubber band with many windings? What made the slowest car so slow?
More science: After seeing how fast and how far a car can go, ask students what happens if they add more weight to the car. Weight can be added by attaching binder clips or taping on small objects. From our lessons on force and motion, do you remember that, if the force stays the same, more mass (or weight) means less acceleration? Is that what students observe? Does adding weight slow down the car?
What other changes could we make to improve the car’s performance? Use different materials? (Lighter materials will result in greater acceleration.) Use a longer rubber band? (Depending on the car design, a longer rubber band might allow more windings and therefore more stored energy.)
An important part of engineering is improving on previous designs. And we can extend that kind of thinking to everything we do in life. We can always look for ways to improve on whatever it is that we’re doing.
One teacher who has done this kind of activity reports, “Our third graders would release the rubber band powered cars in my long empty hallway and then record with different colored stickers where the cars stopped based on the number of rubber band turns. After many classes had added their data points, the students could see patterns and tell stories about what happened to the rubber band–powered cars. They even could have conversations about outliers and made decisions about how to deal with the outliers.”
Never stop learning. ●
How to build a rubber-band-powered car
Matt Bobrowsky is the lead author of the NSTA Press book series, Phenomenon-Based Learning: Using Physical Science Gadgets & Gizmos. You can let him know if there’s a science concept that you would like to hear more about. Contact him at: DrMatt@msb-science.com .
How to build a rubber-band-powered car
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