For the air cannon, participants build pressure in the sealed chamber using a bike pump, and when the valve is turned, the pressure releases, launching the projectile. This activity demonstrates pressure and projectile motion. This activity is popular at Science Expeditions.
Activity/Demo Instructor Notes:
- Setting up:
- Prop the air cannon up in a long hallway using a cord or strap on the legs, 45 degrees or less.
- Connect the bike pump to the valve on the side of the air cannon. You may need to turn or pull the connecting part of the valve.
- Stuff a plastic bag into the cannon, and then the ball. This increases the pressure on the porous ball. It does not need to be all the way at the bottom.
- Running the demo:
- Turn the handle on the other side of the air cannon so it is perpendicular to the body of the cannon, until it hits the metal ridge and cannot be turned further. Explain that this seals the chamber so that pressure can build up.
- For very young participants, you can ask them to turn the handle.
- Ask the participant what they know about pressure. Explain that pressure is force on a certain amount of area. So the bike pump will increase pressure because you’re forcing more air molecules onto the same surface area (the inside of the chamber).
- Ask the participant to build up pressure in the cannon by pumping until the gauge on the cannon (not the bike pump) is past 25 psi.
- When the gauge is past 25 psi, ask them to come around to the other side and quickly turn the handle, which releases the pressure.
- This may take a few trials, but try to adjust the angle of the cannon so the projectile does not hit the ceiling.
- Turn the handle on the other side of the air cannon so it is perpendicular to the body of the cannon, until it hits the metal ridge and cannot be turned further. Explain that this seals the chamber so that pressure can build up.
- Notes/modifications:
- Leakage is more pronounced at higher pressure, which means the pressure may start declining faster than kids can pump as time goes on. If this happens, you can ask a parent to help or help pump it yourself, then guide the participant to wait next to the handle and watch for when it reaches the threshold.
- If there is a long line with lots of kids, you can split siblings/friend groups up into one pumping and one controlling the pressure release handle (and optionally, one trying to catch the ball).
- If there are only a few participants, you can adjust the angle of the cannon for participants to find the angle with the longest distance.
- Ask for hypotheses and why.
- Test the angles.
- Ask for observations. Explain that 45 degrees (or “perfectly diagonal” depending on participant age) will launch the farthest because it has the optimal combination between gravity pulling it down and the initial force from the pressure release.