A new solution for the "reverse sprinkler" problem
arstechnica.com
A new solution for the "reverse sprinkler" problem
1–10 of 19 posts
Re: A new solution for the "reverse sprinkler" problem
#2Hmm, is it possible that this could be partly caused because the water gets sucked not just directly down the pipe, but around the lip of the pipe opening... and one edge of the pipe opening is further away from the center axis of rotation (of the whole sprinkler) than the other end of the pipe opening. I'd think that whether or not this would have an effect could be easily tested by varying sizes of the pipe opening or how far away the opening was from the center to see if it made a difference -- even if the bends in the pipe were the same (the authors seem to attribute the whole effect to the bends in the arms).
Re: A new solution for the "reverse sprinkler" problem
#3Hmm, is it possible that this could be partly caused because the water gets sucked not just directly down the pipe, but around the lip of the pipe opening... and one edge of the pipe opening is further away from the center axis of rotation (of the whole sprinkler) than the other end of the pipe opening. I'd think that whether or not this would have an effect could be easily tested by varying sizes of the pipe opening…
I'll add that this could become particularly important in the 4d case once the sprinkler starts moving. Cause when it's still, the pressure gradient will create a partial-torus like shape around opening, but once it starts rotating, the outer side (rotating around the sprinkler's axis) of the 4D version of this shape has a larger diameter than the inside. So the inner side will be more affected by the environmental water's momentum state than the outside which has more water mass in it's scope rotating around the sprinkler axis.
Re: A new solution for the "reverse sprinkler" problem
#4Why can't you just submerge the sprinkler in water and reverse the flow?
Re: A new solution for the "reverse sprinkler" problem
#5Why can't you just submerge the sprinkler in water and reverse the flow?
That’s what they did
Re: A new solution for the "reverse sprinkler" problem
#6Why can't you just submerge the sprinkler in water and reverse the flow?
Yes that is the experiment. I think when you do that it doesn’t move at all because the effect is tiny so will normally be nullified by friction? And I think the research used very low friction so they could observe the small effect.
Re: A new solution for the "reverse sprinkler" problem
#7I've googled for about 5 minutes trying to understand ....is the "reverse sprinkler" just a device that has been impossible to build so it was a strictly theoretical problem? "We found that the reverse sprinkler spins in the ‘reverse’ or opposite direction when taking in water" - really, this was that impossible to build that nobody knew what it would do? weird
Re: A new solution for the "reverse sprinkler" problem
#8The "inside out" rocket engine is a great explanation.
Re: A new solution for the "reverse sprinkler" problem
#9Doesn't this boil down to time-reversal? I doubt CPT symmetry is relevant here, so I'd be very surprised if it didn't simply reverse the rotation.
Re: A new solution for the "reverse sprinkler" problem
#10Related:
Centrifugal flows drive reverse rotation of Feynman's sprinkler - https://news.ycombinator.com/item?id=39128851 - Jan 2024 (19 comments)
Feynman Sprinkler [video] - https://news.ycombinator.com/item?id=38985308 - Jan 2024 (21 comments; top comment just added to https://news.ycombinator.com/highlights!)
Feynman sprinkler - https://news.ycombinator.com/item?id=14531297 - June 2017 (6 comments)
The Feynman Sprinkler - https://news.ycombinator.com/item?id=11720126 - May 2016 (1 comment)
An elementary treatment of the Feynman sprinkler - https://news.ycombinator.com/item?id=11626758 - May 2016 (1 comment)
Feynman sprinkler - https://news.ycombinator.com/item?id=9710119 - June 2015 (3 comments)