The air pressure cannon is a great demo to do outdoors with a lot of space! It involves using air pressure (supplied with a bike pump) to shoot foam balls out of a Cannon.
Activity/Demo Instructor Notes:
Steps:
- Load balls into the cannon. You can shoot multiple balls out at the same time!
- Make sure the valve on the side of the cannon is closed (perpendicular to the axis of the
- cannon)
- Have the participant pump the bike pump until the pressure gauge on the side of the cannon reads 30 psi
- Have the participant quickly open the valve on the side of the cannon and watch the balls fly into the sky!
Physics explanation:
The bike pump is pumping air through its tube into the closed chamber between the base of the cannon and the valve, increasing the pressure in the chamber. When the valve is opened, the force from the built-up air pressure is transferred to the foam balls.
Sample script:
“When you push on the bike pump, you’re pushing more and more air into the cannon. Right
now, there’s a wall between the bottom of the cannon and the part where the balls are, so the air
can’t get to the balls. We’re putting more and more air in, and it’s pushing on the side of the
cannon! The air really wants to get out! When we turn this valve, the wall goes away and the air
rushes up and pushes the balls out so they go flying!”
Additional notes:
- Small children will have trouble with the bike pump. They also will still want to do it themselves. Consider offering to take turns (and let them do the start and the end) or offering to “help” with one hand.
- The valve needs to be turned quickly, or else the air will just slowly escape and nothing will happen to the balls. For very small children, I would do this step for them.
- Remind kids to watch where the balls are going! They may get so focused on pumping and turning the valve that they forget to watch the launch!
- For when you have more time and a child wants to do the demo over and over again, consider changing the angle between launches. Ask them whether they expect the ball to go further or less far and higher or less high at the new angle. This gets kids really excited! 45 degrees should give the furthest horizontal distance and 90 degrees (straight vertical) should give the highest launch, but the shot-to-shot variation is pretty large, so you might not see the “correct” results. I think the speed that the valve is opened is the greatest factor in ball initial velocity, and this will vary a lot, especially depending on the Child.
- If pumping up the chamber is taking too long or the child is struggling too much, launching from 20 psi will still work! Just won’t get as good of velocity!