[HN Gopher] Feynman Sprinkler [video]
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Feynman Sprinkler [video]
Author : mhb
Score : 76 points
Date : 2024-01-13 22:32 UTC (2 days ago)
(HTM) web link (www.youtube.com)
(TXT) w3m dump (www.youtube.com)
| nadermx wrote:
| That was damn cool. Reminds me of fluids in college. Difficult
| course.
| ShamelessC wrote:
| Perhaps I'm missing something but it all felt sort of
| underwhelming to me? I won't claim to have predicted the motion
| of the thing prior to watching, but watching his demonstration
| was not very surprising or counter intuitive.
|
| What am I missing exactly? I'll admit I only made it about
| halfway through the video...
| samstave wrote:
| Couple thoughts:
|
| The jitter is likely due to the suction pulling the air from the
| outside of the tubes, which then get pulled in the gap between
| the things - which does so in a buffeting fashion due to the
| movement of the pipes, so it finds the oscillation... (the tubes
| are a Foil - so you have to accomodate the flow diff on the
| external and internal of your receiving tube - and how the flows
| from the outside of the foil are a diff speed/flow/rate than the
| center of the tube - thus the light suction guy gets enough
| strength for the outside air to push it back - once it gets far
| enough from the horizontal tube, the pressure from the outside
| flow drops and the lever goes back to its resting position and
| begins again)
|
| The other thing, as he mentioned eddys -- the inlet and outlet
| cones should be turbine-spiral shapes - as the air/fluid comes
| down the pipe, if you give it a spiraling/riffling it will keep
| the flow somewhat cohesive as it spins it.
|
| Further, as a YT comment mentioned - stuffing a bunch of small
| straws in the main tube helps, because if you have a lot of
| smaller tubes - (especially with water) you can get the effective
| "orientation of the molocules" the same - so your stream can be
| more cohesive (this method was (invented?employed) by Disney Land
| Engineers when they were building the fountains that shoot clean,
| cohesive lasers of water.
|
| They run the streams to the fountain through pipes that have a
| ton of staws inside - so the water gets orientated in such a way
| that when the stream leaves the nozzle, the water stays together.
|
| Also - you can test all this in FluidX3d:
| https://github.com/ProjectPhysX/FluidX3D
|
| --
|
| The Eddy Pump was first invented by Leo Davinci... and now we
| have great pumps like:
|
| https://eddypump.com/pump-videos
|
| --
|
| The eddy is the most important thing to understand in fluid
| dynamics IMO. (its what your Heart is, BTW)
|
| ----
|
| @Btrettel:
|
| THANKS! I couldn't think of the term laminar...
|
| And I was simplifying "stuffing straws"..
|
| Appreciate the input. Have you tried FluidX3D?
| btrettel wrote:
| > stuffing a bunch of small straws in the main tube helps,
| because if you have a lot of smaller tubes - (especially with
| water) you can get the effective "orientation of the molocules"
| the same - so your stream can be more cohesive
|
| This is not the right way to think about it. The straws reduce
| turbulence by preventing fluid motion in a radial direction,
| and reduce swirl by preventing a swirling motion. (The screens
| have similar effects.) Both turbulence and swirl prevent the
| formation of a coherent liquid jet. The straws (and screens)
| aren't without disadvantages as they will cause significant
| pressure losses.
|
| How I know: I did a PhD on the range of large fire-fighting
| water jets and ended up reading a LOT of laminar fountain stuff
| online out of curiosity.
|
| > this method was (invented?employed) by Disney Land Engineers
| when they were building the fountains that shoot clean,
| cohesive lasers of water
|
| Definitely employed. Flow straighteners (or flow conditioners,
| or whatever you want to call them) were quite common for
| turbulence and swirl reduction in general before laminar
| fountains appeared. I recall seeing patents with flow
| straighteners for fire-fighting purposes in the 1930s, and I'm
| confident that they were in use in other areas earlier than
| that.
|
| ***
|
| A side note: Laminar fountains are neat, but you'll find a ton
| of misinformation about how they work online. I started writing
| more, but Brandolini's law comes into play, and I don't have
| the time to go into it.
| dreamcompiler wrote:
| > its what your Heart is, BTW
|
| There are certainly eddy currents within the heart, but the
| heart is not an eddy pump. As pumps go, the heart is most
| similar to a reciprocating volumetric pump.
| samstave wrote:
| I should have said "Eddies are fundamental to how the heart
| works" ;-)
| btrettel wrote:
| > Appreciate the input. Have you tried FluidX3D?
|
| Glad to help.
|
| I'm not familiar with FluidX3D. Lattice Boltzmann methods are
| uncommon, probably because they are computationally expensive.
| I'm a finite volume and finite difference guy myself. Finite
| volume methods are the most common approach in computational
| fluid dynamics.
| samstave wrote:
| Do you recall they showed the blip that the google folk made,
| and it was in the hangar at Moffett field... they were
| showing all the different motors and sensors - and it was
| brought up that they had LIDAR sensors pointing at the
| interior helium balloon... and someone asked why they would
| be lidaring the thing...
|
| I surmised that they were using it to calculate the internal
| volume due to the deformation of the balloon as it loses
| volume.... was I correct?
|
| https://techcrunch.com/2023/11/08/the-worlds-largest-
| aircraf...
| btrettel wrote:
| Sorry, blimps aren't my area of expertise. I don't know
| what's going on there.
| samstave wrote:
| Its just a giant helium balloon inside the thing -
| https://youtu.be/FrAc-yORdAo?t=170 - So its "finite" just
| not small.
| mhb wrote:
| "After graduating from Stanford, Fuller worked as an Imagineer
| for The Walt Disney Company, applying the laminar flow
| technology he developed and refined to create Disney's
| "Leapfrog" fountain feature at Epcot Center."
|
| https://en.wikipedia.org/wiki/Mark_W._Fuller
| snewman wrote:
| I had a personal brush with Feynman with regards to this
| experiment.
|
| Circa 1986, I read _Surely You 're Joking, Mr. Feynman_ and
| became mildly obsessed with the fact that Feynman doesn't present
| the result of the sprinkler experiment (see the first few seconds
| of the video for context). A number of colleagues (at the
| software startup where I was working) and I tied ourselves up in
| knots debating what the answer must be.
|
| I wanted to perform the experiment, but lacking materials, skill,
| and (frankly) ambition, I settled for a laughably primitive
| apparatus involving a couple of bendy straws, the bathroom sink,
| and my mouth. This was enough to reproduce the well-known fact
| that if you push water out through the sprinkler, it will spin.
| When I tried sucking water in, it would give a momentary
| rotational jerk and then stop moving... but perhaps that was due
| to my mouth tightening up on the straw?!?
|
| After I shared this inconclusive result, one of my co-workers
| decided to get to the bottom of the matter. He called the
| Pasadena operator, asked for the home phone of a Mr. Richard
| Feynman, and - to my utter horror - dialed the number.
|
| It seemed impossible that this was a viable procedure for making
| contact with a Nobel Prize-winning physicist, but through the
| speakerphone, we could all hear a gruff voice that certainly
| sounded like it might be him. All doubt was removed when my
| friend explained that we were looking for the answer that isn't
| presented in the book, and the gruff voice said, "Why should I
| tell _you_? "
|
| Feynman then asked whether we had tried the experiment, and to my
| redoubled horror, the phone was handed to me. I stumbled through
| some explanation of what I had tried and what result I had
| observed. Fenyman then relented, and explained the entire
| situation in ten short words:
|
| "The sprinkler cannot rotate, because no angular momentum is
| transferred."
|
| (Not an exact quote, but something very much like that)
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