Vote 2020 graphic
Everything you need to know about and expect during
the most important election of our lifetimes

Watch Dye Avoid A Column That Isn't There

No trick. Liquid dye in water lets us see a Taylor column, which is a physical column made of nothing. Dye creeps around it, or occasionally creates it. We'll tell you how it works, and why it affects more than just an experiment in a fluid dynamics laboratory.

Advertisement

In still air, or water, Taylor columns don't exist. Instead of a column, there is just a little disk or puck on the floor. Gas and water flow over it with no problem whatsoever.

Once the ground the puck is on starts spinning, things change. The disk spins with the ground. The small disk forms a tall invisible column. Drop something inside it, and that something stays. Release liquid (or gas) next to the column, and as the liquid moves, it will part around the column, unable to penetrate it. If you wonder about what kind of ground spins that quickly, creating conditions such as these - you're standing on it.

Advertisement

Taylor columns form because, contrary to many people's expectations, spinning a liquid around doesn't necessarily make its motion more chaotic. It can impose order, because in a spinning liquid particles tend to get nudged back toward their original position like they're in a kind of whirlpool. This helps stem the expansion of released gasses or liquids because, in order for dye to move into a space, the existing water has to move out of it. If the water doesn't move up, move down, or move aside, the dye can't move in. As a result, a spinning liquid can form odd, rigid "columns" of material parallel to the axis of rotation.

The first video shows a column of dye forming in a spinning vessel. This second video gives you multiple looks at how a Taylor column forces dye to move around it, even though it doesn't have any solid barrier. You can also see how dye reacts when the container is not being spun.

[Via Weather in a Tank.]

Share This Story

Get our newsletter

DISCUSSION

I think your explanation of Taylor columns kind of misses the point, even though the Wikipedia page for Taylor columns says basically the same thing. The Wikipedia page for the Taylor-Proudman theorem has a small section on Taylor columns (which are an effect of the Taylor-Proudman theorem), and that explanation is better. Also with a quick Google search I found this page, which gives a good explanation with diagrams.

The Taylor-Proudman theorem states that in a homogenous, inviscid, rotating fluid, velocity will be uniform along lines parallel to the axis of rotation (in this case, vertical lines). Picture a column of water as being like a pencil standing vertically on its eraser end: it can slide around horizontally, but the whole column must move together; it can't tilt, have different parts of it move in different directions, and it can't move vertically (moving the column up, for instance, would force water to come in from the sides to replace it at the bottom, which would mean that the water rushing in at the bottom would be moving in a different direction than the water above, which breaks the rules). Now put a puck on the bottom of the tank. You can picture that the water at the very bottom of the tank will flow horizontally around the obstacle. Now, because the whole column of water above it has to move together as one, the full depth of the water must also flow horizontally around the obstacle. Put another way: because the water at the bottom can't move in the direction through the puck, the water above can't move in the direction over the puck. And since no water from outside the column above the puck can move into the column above the puck, that water above the puck is stuck there, too (nothing could replace it if it moved).

So it's not really a matter of water in a rotating fluid returning to its original location. The water can move, but if it's not already over the puck, it can't move over the puck, and if it is already over the puck, it can't move off of it.