Students first examine their balloon cars closely to explore how they work, and do some mini-experiments to see what role each part plays. Next, there are some focusing questions that help to review and develop energy concepts related to balloon cars. Finally, they write descriptions about how balloon cars work.
Ask students what they have noticed about the way a balloon car works. Chart their observations. Here are some focusing questions that might help to structure the discussion:
Balloon car experiments.
Here are two guided experiments (or demonstrations) that reveal more about how balloon cars work:
Adjust the balloon and straw so the straw points sideways to the car (see a video) , perpendicular to the direction the car is supposed to go. Try the car.
Replace the straw so it is again pointing to the rear. Adjust the front axle so it is at an angle with the rear axle, instead of parallel to it (see a video. Try the car.
* What happens now?
* What controls the direction of the car?
The class analyzes the information from these experiments, then breaks down what happens from the time they begin to blow the balloon up to when the balloon car is traveling on its own. Help students describe each step in terms of what is happening with the energy. These questions might help:
Extend the concept of energy to include the different forms of energy, the transformation of energy from one form to another, and the conservation of energy. Do this with reference to both wind-ups and balloon cars, making connections with what students have done in this unit. Here are explanations of energy relationships, conservation of energy, and of situations where energy does not seem to be conserved: friction and the wind-up and friction and the balloon car.
Students complete the worksheet “How a Balloon Car Works”.
Use this to assess students’ understanding of energy concepts for this unit.