An air-pressure cannon is a simple school project that uses a plastic bottle, a balloon, and a soft projectile to show how moving air can do work. When you pull back the balloon and let go, the air inside the bottle is pushed forward. That moving air can launch a cotton ball or pom-pom across the room.
This project matters because it turns invisible air pressure into something students can see and measure.
The stretched balloon stores elastic potential energy, which changes into kinetic energy when the balloon snaps back. As the balloon moves inward, it decreases the space for the air inside the bottle and creates a quick pressure push. The pressure difference makes air rush out of the bottle opening, carrying the soft projectile with it.
Students can test how launch distance changes with pull distance, bottle size, projectile mass, and launch angle.
Key Facts
- Pressure is force spread over area: P = F / A.
- A stretched balloon stores elastic potential energy before release.
- When the balloon snaps forward, it pushes air and creates a short burst of higher pressure.
- Moving air can transfer energy and momentum to a soft projectile.
- Greater pull distance usually gives the projectile more kinetic energy, but only up to the safe stretch limit of the balloon.
- Kinetic energy depends on mass and speed: KE = 1/2 mv^2.
Vocabulary
- Air pressure
- Air pressure is the push caused by air molecules colliding with surfaces.
- Elastic potential energy
- Elastic potential energy is stored energy in a stretched or squeezed object, such as a balloon.
- Kinetic energy
- Kinetic energy is the energy an object has because it is moving.
- Projectile
- A projectile is an object that is launched and then moves through the air.
- Momentum
- Momentum is a measure of how hard it is to stop a moving object and depends on its mass and velocity.
Common Mistakes to Avoid
- Using hard projectiles is unsafe because the cannon can still transfer enough energy to hurt someone or damage objects. Use only cotton balls, pom-poms, or other soft materials.
- Pulling the balloon too far is wrong because it can tear the balloon or make the launch inconsistent. Use the same safe pull distance for each test.
- Changing several variables at once makes the results hard to understand. Test one factor at a time, such as pull distance, projectile mass, or launch angle.
- Assuming the projectile is pushed by the balloon itself is incorrect. The balloon pushes the air, and the moving air pushes the projectile out of the bottle.
Practice Questions
- 1 A student pulls the balloon back 4 cm and the pom-pom travels 120 cm. On the next trial, the student pulls the balloon back 6 cm and the pom-pom travels 180 cm. How many centimeters farther did the pom-pom travel on the second trial?
- 2 A soft projectile has a mass of 0.004 kg and leaves the bottle at 5 m/s. Use KE = 1/2 mv^2 to calculate its kinetic energy.
- 3 Two students use the same bottle and the same pull distance, but one uses a cotton ball and the other uses a heavier pom-pom. Explain why the two projectiles might not travel the same distance.