Reversible Flow

August 17, 2007 4:32 PM

Reversible flow! In the 1960s, the National Committee for Fluid Mechanics Films produced a series of films for education in fluid mechanics. This clip is part of "Low Reynolds Number Flow"; you can find the entire collection streamed here. Interesting demonstrations abound. (1st link is QT; rest are RealPlayer.)
posted by Upton O'Good (19 comments total)

We watched some of these videos in my fluids class in college. The reversible flow demonstration never ceases to amaze me. Very cool. Thanks for posting these.
posted by SBMike at 4:51 PM on August 17, 2007

Mesmerizing.

Wikipedia on the Reynolds number.
posted by grouse at 5:10 PM on August 17, 2007

Holy crap, what a great party trick! How complicated / expensive is the setup?
posted by ZakDaddy at 5:45 PM on August 17, 2007

WTF. There was no audio for me--how did they do that?
posted by DU at 6:35 PM on August 17, 2007

Another cool demonstration is when he writes "R<<1" in syrup, deforms it beyond recognition, then returns it to its original state.
posted by [expletive deleted] at 6:37 PM on August 17, 2007

I stumbled across that link a few weeks ago. Had no idea what the experiment was going to do, how it'd turn out.

So when the syrups did their thing on the reverse spin, I nearly fell out of my chair. It completely blew me away. One of the neatest science tricks I have ever seen.
posted by five fresh fish at 6:56 PM on August 17, 2007

This is astonishing but would be 3x better if there were a link to an explanation of why this happens.
posted by lupus_yonderboy at 11:29 PM on August 17, 2007

A wizard did it.
posted by ROU_Xenophobe at 12:02 AM on August 18, 2007

Very low inertia (or very high viscosity) means you can't keep going in a straight line at constant speed (like you could in say, space), so you, the particle, just keep moving along with the stuff around you. Which means if that rod spins you around four times and then spins you back four times, you pretty much end up back where you started.
posted by dirigibleman at 1:21 AM on August 18, 2007

All this talk about syrup...
posted by aubilenon at 1:24 AM on August 18, 2007

Fascinating video, thanks. I bet it was a pain to clean up after al the syrup tricks.

Although it is not necessary to calculate Reynolds number in medical practice, the concepts are quite broadly applicable. For example, the transition from laminar to turbulent flow (generally occurs around R=2000) is what produces heart murmurs, wheezing (as in asthma) and stridor. Fluid mechanical concepts are important to understand the function of medical equipment such as gas flowmeters and venturis and many other things.
posted by TedW at 4:08 AM on August 18, 2007

The wikipedia article grouse linked includes a link to this nifty article on Reynolds number and biology

God I feel like such a nerd, doing this on a Saturday morning before anyone else is up.
posted by TedW at 4:21 AM on August 18, 2007

Less sucktastic format versions are available on youtube. For example this
posted by Big_B at 8:53 AM on August 18, 2007 [1 favorite]

Gotta love the YouTube comments:

geefer123 (1 month ago)
photoshopped

tomomazo (3 weeks ago)
fake.

biohazd (3 weeks ago)
that better have been a joke tomomazo.

tomomazo (3 weeks ago)
its cgi you can tell.

Sephirothson (3 weeks ago)
You can? How so? I would love an explination of how you can tell it's CGI.

In the style of XKCD: Science, it works...

tomomazo (3 weeks ago)
you can tell its cgi by the hands because they have no fingernails!

jackal0jackal (3 weeks ago)
You blow it off as CGI because you don't know any better. I have professional experience with laminar flow both in my work as a nuclear reactor technician in the Navy and in my current job in semiconductor manufacturing. It's 100% real.

tomomazo (3 weeks ago)
your lieing, its a hologram or somthing.

posted by grouse at 9:00 AM on August 18, 2007 [2 favorites]

Science: your lieing, its a hologram or somthing
posted by quin at 11:24 AM on August 18, 2007 [1 favorite]

Whatcha wanna bet the people who don't believe fluid dynamics explains this, simultaneously believe in a god?
posted by five fresh fish at 12:14 PM on August 18, 2007

The dude's ignorance is even more hilarious because he is convinced that it's a fucking hologram, and not a demonstration of scientific principles. He believes in the made-up, nonexistent technology and not the science.
posted by synaesthetichaze at 6:44 PM on August 18, 2007 [1 favorite]

Or a troll.
posted by five fresh fish at 8:11 PM on August 18, 2007

great post. Thanks.
posted by marvin at 11:06 PM on August 18, 2007