Science Buddies: "Ask an Expert"

Hello,
I am working on A Change in Winds project found in the physics section, and my dad and I cannot get the cans to collide no matter how many times we try. I don't know if it's that we are putting the cans right to the door, or that we might just be doing anything wrong. Please give me some guidance!

yoojini - I have to admit I'm not sure what the stopwatch portion of the experiment is about, but let's try to get the basics operating first. I would think that the higher velocity air flow between the cans would definitely bring them closer together. If the air stream spills over to the outside of the can it will negate the pressure differential and reduce the tendency of the two cans to move toward each other. I would try a narrow nozzle on the hair dryer to produce an airstream no wider than the space between the cans. I would also place the nozzle fairly close to the cans, no more than a several inches away, to start, to reduce diffusion of the air stream. Did you notice that the cans were getting closer in your test, just not touching? If so, you are observing the Bernoulli effect, some problem with the airstream is just not providing sufficient action. Are the cans positioned several feet down from the point where they are attached to the door frame.? The string should be a few feet long, at minimum. Try a few of these variables. The Bernoulli effect should be be easily demonstrated by this experiment. It just sounds like a small set-up error.

Rick Marz