Feynman's reverse lawn sprinkler.

Get your science fix here: research, quackery, activism and all the rest
Post Reply
User avatar
Boustrophedon
Stummy Beige
Posts: 2861
Joined: Mon Nov 11, 2019 3:58 pm
Location: Lincolnshire Wolds

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.
Hjulet snurrar men hamstern är död.

User avatar
shpalman
Princess POW
Posts: 8244
Joined: Mon Nov 11, 2019 12:53 pm
Location: One step beyond
Contact:

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.
having that swing is a necessary but not sufficient condition for it meaning a thing
@shpalman@mastodon.me.uk

User avatar
Pucksoppet
Snowbonk
Posts: 599
Joined: Mon Nov 11, 2019 8:13 pm
Location: Girdling the Earth

Re: Feynman's reverse lawn sprinkler.

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


User avatar
Boustrophedon
Stummy Beige
Posts: 2861
Joined: Mon Nov 11, 2019 3:58 pm
Location: Lincolnshire Wolds

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.
Hjulet snurrar men hamstern är död.

User avatar
Boustrophedon
Stummy Beige
Posts: 2861
Joined: Mon Nov 11, 2019 3:58 pm
Location: Lincolnshire Wolds

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.
Hjulet snurrar men hamstern är död.

User avatar
shpalman
Princess POW
Posts: 8244
Joined: Mon Nov 11, 2019 12:53 pm
Location: One step beyond
Contact:

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
having that swing is a necessary but not sufficient condition for it meaning a thing
@shpalman@mastodon.me.uk

User avatar
Boustrophedon
Stummy Beige
Posts: 2861
Joined: Mon Nov 11, 2019 3:58 pm
Location: Lincolnshire Wolds

Re: Feynman's reverse lawn sprinkler.

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

Hjulet snurrar men hamstern är död.

User avatar
dyqik
Princess POW
Posts: 7527
Joined: Wed Sep 25, 2019 4:19 pm
Location: Masshole
Contact:

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.

Post Reply