Funnel with ping pong ball
You have a funnel with a ping pong ball in it. If you are holding
it in the upright position, what happens to the ping pong ball
when you blow into the funnel?
Not much. It will lift slightly from the funnel and then, the air
rushing around its side will create lift, pulling the ball back
into the funnel. If you can get a nice, steady, source of air (e.g.,
blow up a large balloon, attach it to the funnel and, with the ball
in place, let it start to deflate slowly) you should be able to turn
the funnel upside down without the ball falling out.
Of course, if you puff, instead of blowing steadily, you can pop the
ball out of the funnel.
A similar experiment can be done with a floor fan. Point it toward the
ceiling and place a beach ball or balloon (partly inflated) over it.
It should float over the fan for several minutes instead of blowing
away. See how far from the center of the fan you can let the ball go
and still have it pull into position over the fan.
Lift is caused by air moving faster over one side of a ball or wing than
it moves over the other side. The lift is such that the ball or wing
moves toward the side with the fastest moving air.
Hope this is useful!
gregory r bradburn
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Update: June 2012