Twist in Time - Laminar Flow You've heard about color mixing. What about color unmixing? email to friend
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Watch the video for a complete explanation of the experiment.

How does it work?

Editor's Note - It's fun for us to see Steve Spangler in a complete stage of amazement and confusion and obsessed with wanting to learn more about a science demo. We get calls every day from physics professors who all have their unique way to explain this demonstration. Please know that this explanation will evolve over time as we learn more and try to wrap our minds around the science of Laminar Flow.

 

Steve Spangler was first inspired to recreate this demonstration after seeing Dr. Kevin Cahill, from the Department of Physics and Astronomy at the University of New Mexico, first present this on video. We have contacted Dr. Cahill and hope that we can have him share his explanation.

Here's the best explanation we have... so far.

I believe what's happening here is very low Reynold's number laminar flow, which means that there are many parallel layers of "sticky" (or viscous) fluid. As the handle is turned, the dyes remain within their original layers and do not mix with each other, even as they are spread out over their individual layers. As the crank is turned backwards, the process is inverted, and since there is no fluid turbulence in laminar flow, the process can be inverted almost perfectly.

Online Buzz

It's amazing to read comments about this demonstration on sites like YouTube, Metacafe and others. Here is just a sampling...

• This is a total fake. You can tell that the video was just played in reverse. I can't believe people fall for this.
• Are you out of your mind, it's a real demonstration of Laminar Flow. I saw it in college.
• Because the fluids involved are thick and movement is slow, the flow stays laminar and not turbulent.
• There is really no mixing. If one day you tried to mix 2 thick paint colors, you know things are not easy to do without a thorough mixing! The video should have shown what happens if we move the cylinders far faster.
• Leave the beads of colored corn syrup set. How long would it take them to diffuse? In highly viscous fluids, diffusion is practically non-existent. What we are observing is in fact chaos (small, uncontrollable variations in speed, vibrations, etc.) that cause them to lose their form.
• With low Reynolds number (Re < 1) those kinds of processes are reversible because the flow remains laminar (as opposed to turbulent). As long as the process is not turbulent, substances in the medium will not mix.
• I think this is not something reversible, fluid layers flow independently and dyes don't diffuse into neighbouring layers. Think of this flow as people starting in rows entering a curve and speeding the curve with the same angular velocity, as the hands of a clock, observing them from outside they seem a disordered crowd, but looking them from upside they are disposed as curved rows, so that when you revert the motion, they return in place.
• The philosophical interpretation of this phenomena leads us to think about how something can leave its original form but still "be there" and then return. It's a clear example of how subjective or empiric science can be and that, perhaps, instruments are the only limit to knowledge.
• The trick is putting the dyes at different depths, or putting them in a way that they radiate from the center in different orbits. This is so when you turn the glycerin, they all create separate orbits, when seen horizontally, they look like they mix, but it's an illusion by interposition. When you wind them back they will have been conserved.