3 ms·

Could you do that with a spoon in a large bowl? Or does the unmixing need to be extremely precise?

• wiredfool 15y ago
  The 'mixing' needs to be as pure laminar flow as possible, and that's generally between two cylinders that are rotating at different speeds. The speed of the fluid across the space should be a linear function of the relative distance from each wall. Any variation of that is going to reduce the reversability. So what they're doing is very carefully not mixing, but shearing. The fluid here is behaving like a very soft chunk of rubber, not like any fluid that you're used to dealing with. If you've got a spoon, there's going to be some turbulence as the flow goes around the edges and the flow detaches from the surface. Turbulence absolutely destroys the reversibility.
  • kenjackson 15y ago
    Thanks. You just saved me cleaning up a big mess in the kitchen.
• onedognight 15y ago
  You can use a spoon, but yes you have to extremely precise. What matters is that you exactly reverse your forward motion. It's an entirely geometric effect though, so it doesn't matter how fast you go forward and backwards as long as you stay slow enough to be in the Stokes regime.