Helicopter & Launcher
As this toy helicopter falls, the blades encounter air. The blades are at an angle, so that each little bit of air that hits them bounces off and pushes them to the side. If you have them bent correctly, each one will be pushed in the opposite direction, causing the helicopter to spin. The air also pushes up the blades, causing the helicopter to fall slower than if it were just tumbling randomly.
Real helicopters do this in emergencies. If a helicopter’s engine fails, the recovery procedure is to begin “autorotation.” This simply means that instead of the engine turning the blades, the air flowing past the falling craft will turn the blades. In most cases, this provides enough upward force to insure a slow decent, allowing the pilot to find a suitable space below for an emergency landing.
This toy requires air to function. If you tried it on the moon, it would spin just fine, but would get no force of lift since there is no air.
Let’s follow the energy used in this project. You provide the original energy to launch this helicopter. Your body got this energy by metabolizing the food you ate earlier. When you pull the string in the launcher, you are putting you energy into the helicopter. The helicopter begins spinning, the blades push down on the air so the air pushes up on the blades, and the helicopter begins to rise. As the helicopter leaves either your hand or the launcher, it is traveling as fast as it will go during its flight.
The helicopter slows down as it continues upward because gravity is pulling steadily downward on it and because the air drags on the blades. It loses kinetic energy as it gains potential energy of height. At its highest point, it stops moving up and has lost all linear kinetic energy. Since it is rotating though, it also has rotational kinetic energy. At the high point, it holds the maximum potential energy of height it will have. It then returns down, exchanging that potential energy for kinetic energy as it accelerates toward the ground. Some of the helicopter’s potential energy goes into pushing the blades around through the air, so the speed (and kinetic energy) of the helicopter is less on the way down. Upon impact with the ground, all remaining energy is converted to heat. You won’t feel this heat because there is not much energy involved. But if you clap your hands together hard, you’ll feel the heat of impact.
Air is real. You can’t see it, but it moves things.
As the helicopter begins to spin, the blades push off the air and it gets an upward force.
When it reaches it’s highest point and starts falling, the air that it encounters makes it spin around and fall slower.
What do you think would happen if you made the helicopter heavier at the bottom?
How could you make the helicopter go up farther?
What are some differences between this helicopter and a real helicopter?
What would happen if you tried this project on the moon?