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Many have seen those science displays in which a ball is suspended in a column of moving air. Small versions use a pipe for the mouth and a pingpong ball. The flow creates low pressure around the ball, and so if the ball moves, the flow tends to pull it back to the center. I am sure this effect has
a name. The same effect works with water - place an empty can in the sink, allow a thin steady stream of water to flow over it, and try to roll it. It will roll back so that the stream is on it.
I propose that this effect be used for a fountain sculpture. It would consist of bowling ball sized spheres balanced atop sharp pointy pyramids. Each ball would have a steady drizzle of water falling on it, which would keep it balanced. They would jostle and jiggle in the breeze. Passers-by would marvel.
Wikipedia: Bernoulli's principle
http://en.wikipedia...rnoulli's_principle
"I'm sure this effect has a name." [jutta, Jul 21 2006]
Who needs pyramids and water when you got this guy?
http://www.guinness....asp?recordid=52895
[DrCurry, Jul 23 2006]
[link]
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I'd marvel, too. You might be able to get this to work if you had an array of high-speed jets around the ball. As is, the weight of the ball will overpower the righting force of the drizzle of water. (Notice that your empty can is empty and rolling.) It's something about linear displacement moment and sine righting moment. |
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The name is the Coanda Effect, I think. |
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replace the pyramids with pointing fingers,
make the balls spin by introducing a
tangential force, and win another croissant
in addition to this one + (I'm allowed to
give two per idea now) |
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why do you get two [xenxag]? is it some
secret superpower bestowed upon those
deemed worthy? |
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You are not worthy (link). |
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[edit] Link deleted, see below. |
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[bacon], you may be right about the balls being too heavy. Solution: hollow balls. Who would every suspect a bowling ball might be hollow? Hollow spheres of basalt might be even niftier. |
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//bowling ball sized spheres// My bad--I just assumed the spheres were solid. "jostle and jiggle in the breeze" should have given it away. |
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The air version is a demonstration of Bernoulli's principle - the fast-moving air of the stream is less dense than the non-moving air around it. I'm not sure the water version works the same way. If you're rolling a can away from under a stream of water that is flowing vertically downwards, the water exerts pressure that the shape of the can translates into rolling motion back under the flow. If you just pushed on the can with your finger, it would roll back! |
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Would a hollow sphere made of a carbon fiber shell be niftiest? |
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I was surprised about the can in the water because it seemed counter intuitive - if you push down on a can off center with your finger,the can moves away from your finger - just like pushing on a watermelon seed shoots the seed away. However the water pulls the can back towards the water instead of pushing it away. I think that to work, the water must be flowing over the can on both sides of the can,and the can moves towards the side with more flow, equalizing at a position where flow is the same. |
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You may be right that the water and air examples are not the same thing. The water may be an example of the mysterious shower curtain effect. |
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[jutta] Deleted. Sometimes I get the feeling that humor is acceptable for others here, but when I indulge in it I have sinned. The play of words on "worthy" seemed appropriate. |
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[normzone] all words are equally worthy,
but some are more equally worthy than
others. |
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Hey, didn't mean to rain on your parade. I'm just touchy when it comes to commercials. |
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