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My dad and I tried to build a steam piston. We used bicycle tube valves to let air into each end of a plastic tube. Each end has another bicycle tube valve to let air out. Inside the tube there is a piston that was supposed to move back and forth. It didn't move. We think the valves don't let enough air into the two inch cylinder. We started to fool around with the tube and put a plastic golfball in. We connected a bicycle pump to one end and left the other end open. When we pumped air into the cylinder, the ball did not shoot out as we expected. It shot back quickly against the end where the air was coming into the cylinder. Why didn't our piston work, and why does the ball come back and not away from the air? This is fun science. Thanks for your help.
Question Date: 2006-02-04
Answer 1:

Given the clearance between the golf ball and the cylinder, I am guessing Bernoulli's principle may be at work here. Basically, it states that the higher the air (in this case) speed, the lower the pressure. I am not sure how exactly it would work in your case, given the geometry of the air flow past the golf ball within the cylinder. If the cylinder is transparent, would it be possible for you to send me a photograph (or better yet, a small .avi movie)?



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