What grade r u in
Why don't u make pneumatic ping pong gun because I just finished making one and it will fire a ping pong over 75ft posted from my iPhone
Pneumatic potato cannon. They work well. Maybe a mini one possibly.
When you squeeze it, the pressure inside increases, making his eyes and...ears(?) pop out. Then again this is neither pneumatic or hydraulic, so I would suggest you create a spud cannon. This is also known as a potato cannon. Maybe figure out a way to increase the pressure inside the barrel by decreasing the size of the barrel as you squeeze water out the barrel, thus pushing the potato along with the water, out with great force. Basically, use the same principle that a washing machine does. Since it takes huge amounts of force to even compress water slightly, as the pressure remains constant in a large tube, the water pressure will increase as the size of the tube decreases. This is how a washing machine is able to achieve large psi numbers from the nozzles while only compressing the water near the water intake at around 10 psi.
A super-soaker water gun. A water rocket, car or boat. A ping pong ball cannon.
+1 There are some truly epic water rocket designs on this site, such as the ones by oscarthompson.
Lung powered marshmellow shooter.
Balloon car. Scale models of hydraulic systems (a drawbridge with pistons, elevator, automobile lift). Barometer.