Introduction
Turn a pile of trash into a toy car—and watch it go! In this activity you will learn some physics concepts and use recycled materials to build a toy car that is propelled by a balloon. You can even find a friend, build two cars and race them against each other. Whose car will go the fastest?
It might not seem like it at first, but a simple balloon car is loaded with physics and engineering concepts! When you inflate a balloon, it stores potential energy in the form of stretched rubber and the compressed air inside. When you release the balloon, this energy is converted to kinetic energy—the energy of motion—as the balloon zooms around the room. Some of the energy is also converted to heat due to friction. According to the law of conservation of energy, the total amount of energy is conserved. Energy never “disappears”—it just changes to another form.
Another way to think about the balloon's movement is to use Newton's third law of motion: For every action there is an equal and opposite reaction. When you inflate a balloon and then release the nozzle, the rubber contracts and pushes the air out the nozzle. This means that there must be an equal and opposite reaction—the air pushes back on the rubber, propelling the balloon forward. This principle is used in real rockets and jets that shoot a high-speed stream of gases out the back of their engines, propelling the vehicle forward. In this project you will use this principle to build a toy car that is propelled forward by the stream of air escaping a balloon as it deflates.
The car also contains a simple machine: the wheel and axle. This invention has been around so long, we take it for granted—and many of us ride in wheeled vehicles every day. You will see, however, getting your wheel and axle to spin smoothly is a critical part of getting your balloon car to work!
