Twist in Time – Laminar Flow
You've mixed colors, but have you ever unmixed and separated them?
It’s a demonstration that almost has to be seen in person to believe. As you’re watching the video, please remember that there is absolutely no trick photography. When disbelievers see the demonstration performed, the reaction is nothing short of astonishing. A scientists, we know color mixing is not a reversible process. Mix red and blue and you make purple. Separating the colors back into their original form is not only tricky but unimaginable for many of us. Watch the video… you’ll see why we call it a “Twist in Time.”
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Fill the larger of the two glasses 1/3 full with clear liquid soap.
Place the smaller glass inside the large soap filled glass.
Fill the smaller glass with water so that the water is level with the top of the larger glass.
Clip three of the large binder clips around the rim of the larger glass. Make sure they are evenly spaced and leave a spot for the final clip to be added later.
Add a little soap to each of the three small cups and mix in two drops of food coloring. Each cup of soap needs to be a different color.
Use the three pipettes, one for each color, to add a small amount of colored soap to the clear soap inside the larger glass. Be sure to insert the colored soap below the surface of the clear soap.
Add the final binder clip to the empty spot of the larger glass.
Slowly rotate the smaller glass in one direction. You will see the colors begin to mix inside of the soap.
Now, rotate the smaller glass in the opposite direction. The colors will begin to separate and “unmix!”
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.
The most widely accepted view of what is 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.
Take It Further
How many times can you twist and untwist the colors before they no longer separate?
Science Fair Connection
Preforming this Twist in Time- Laminar Flow activity is pretty cool, but it isn’t a science fair project, yet. You can create a science fair project by identifying a variable, or something that changes, in this experiment. Let’s take a look at some of the variable options that might work:
- Instead of just using one brand of clear liquid soap, compare the results if you conduct this activity with several different brands of clear liquid soap. Are they each the same thickness and do they produce the same results?
- Try this activity with other clear viscous (thick) liquids. Determine how the viscosity of the liquid changes the effects of the mixing and the unmixing of the colors.
These are just a few ideas, but you aren’t limited to them! Try coming up with different ideas of variables and give them a try. Remember, you can only change one thing at a time. If you are testing different brands of clear soap, make sure that the other factors remain the same!
It’s amazing to read comments about this demonstration on sites like YouTube and other sources. 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.