Which way will the whirling sprinkler spin in this experiment? And why?

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Put one of these whirling lawn sprinklers at the bottom of a pool, connect its hose to the pool's open drain, and then pool will drain out through the sprinkler. 

Which way does the sprinkler spin, and why? 

For this experiment, assume that the sprinkler spins clockwise under normal use (sitting on a lawn with the hose connected to a water supply).


Offline Nizzle

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Trick question?

I think there will be no spin at all.
Why? because my gut tells me..
« Last Edit: 16/10/2009 15:12:00 by Nizzle »
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Offline LeeE

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Assuming that the sprinkler head rotates due to offset jets and not a rotor in the base, I don't think it will rotate at all if the water is simply drained through it.  However, if you were to suck water through it by virtue of a pressure difference, I think it would then rotate 'backwards', as it were.

The difference between simply draining and drawing water through it (due to a pressure differential) is that when you draw water through it you'll be trying to create a void in the medium, creating a region of low pressure, just in front of the nozzles whereas if the water is just being drained through it, the 'void' occurs at the surface, or top of the water column, and the pressure at the nozzles will be unchanged.

I think  [;D]
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Offline daveshorts

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The fluid can only impart a rotation to the spinner if the fluid is caused to rotate in th opposite direction. When the fluid flows out of the tubes it forms jets which have an overall rotation so the spinner rotates the other way.


The flow pattern when sucking is very different and if the tubes are thin then spherically symmetric, so the fluid isn't rotating.


I am not entirely sure if the asymmetry caused by the pipe getting in the way of the fluid sucking will produce any net rotation