Feynman's reverse lawn sprinkler.

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Boustrophedon
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Feynman's reverse lawn sprinkler.

Post by Boustrophedon » Sun Jan 26, 2020 5:15 pm

No not a euphemism nor a medical complaint, but a question explored by Richard Feynman in "Surely You're Joking Mr Feynman": Namely what will a rotary type, Heron's turbine type lawn sprinkler do if you immerse it in water and it sucks instead of blows. Will it go round and if so in what direction?

Will the pressure X Area at the nozzle suck it forward? Or will the momentum change around the bends push it backwards.

Feynman did not directly answer the question in the book, he only reported in the damage and mess he made, actually doing the experiment. I was moved to ask after contemplating the forces on an immersion blender whilst making Yorkshire puddins.
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Re: Feynman's reverse lawn sprinkler.

Post by shpalman » Sun Jan 26, 2020 5:46 pm

James Gleick's biography of him recounts the experiment and gives the answer. The difference between squirting and sucking is the angular momentum of the water. When it leaves in a jet it has one (with respect to the centre of the sprinkler) when it's sucked in from more or less all directions it doesn't.

So it doesn't go around.
molto tricky

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Re: Feynman's reverse lawn sprinkler.

Post by Pucksoppet » Sun Jan 26, 2020 5:49 pm


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Boustrophedon
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Re: Feynman's reverse lawn sprinkler.

Post by Boustrophedon » Sun Jan 26, 2020 6:01 pm

shpalman wrote:
Sun Jan 26, 2020 5:46 pm
James Gleick's biography of him recounts the experiment and gives the answer. The difference between squirting and sucking is the angular momentum of the water. When it leaves in a jet it has one (with respect to the centre of the sprinkler) when it's sucked in from more or less all directions it doesn't.

So it doesn't go around.
Which is what I reasoned, but as events and Youtube videos show, I was wrong.
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Boustrophedon
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Re: Feynman's reverse lawn sprinkler.

Post by Boustrophedon » Sun Jan 26, 2020 6:02 pm

Boustrophedon wrote:
Sun Jan 26, 2020 6:01 pm
shpalman wrote:
Sun Jan 26, 2020 5:46 pm
James Gleick's biography of him recounts the experiment and gives the answer. The difference between squirting and sucking is the angular momentum of the water. When it leaves in a jet it has one (with respect to the centre of the sprinkler) when it's sucked in from more or less all directions it doesn't.

So it doesn't go around.
Which is what I reasoned, but as events and Youtube videos show, I was wrong. And Wiki too.
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Re: Feynman's reverse lawn sprinkler.

Post by shpalman » Sun Jan 26, 2020 6:21 pm

The puzzle of the steady-state rotation of a reverse sprinkler: https://dash.harvard.edu/handle/1/27413727
The continuous rotation of the reverse sprinkler has been a puzzle for over two decades. This article presents a series of experiments that demonstrate that a properly designed reverse sprinkler experiences no steady-state torque and does not rotate. Ignoring transients when the flow starts and stops, if any sustained rotation of the reverse sprinkler occurs, it is because a force couple produces a torque accompanied by vortex flow inside the body of the sprinkler. No steady-state rotation occurs if the vortex is suppressed or prevented from forming in the first place. Demonstrative proof is given that an ideal reverse sprinkler does not rotate.


https://sciencedemonstrations.fas.harva ... -sprinkler
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Re: Feynman's reverse lawn sprinkler.

Post by Boustrophedon » Sun Jan 26, 2020 7:10 pm

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Re: Feynman's reverse lawn sprinkler.

Post by dyqik » Mon Jan 27, 2020 2:54 am

Boustrophedon wrote:
Sun Jan 26, 2020 5:15 pm
No not a euphemism nor a medical complaint, but a question explored by Richard Feynman in "Surely You're Joking Mr Feynman": Namely what will a rotary type, Heron's turbine type lawn sprinkler do if you immerse it in water and it sucks instead of blows. Will it go round and if so in what direction?

Will the pressure X Area at the nozzle suck it forward? Or will the momentum change around the bends push it backwards.

Feynman did not directly answer the question in the book, he only reported in the damage and mess he made, actually doing the experiment. I was moved to ask after contemplating the forces on an immersion blender whilst making Yorkshire puddins.
This was a question on my Physics degree final paper.

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