A liquid floating upon another

In summary, the conversation discussed the concept of a high density liquid sitting on top of a low density liquid in a beaker. The question was raised about what would cause the high density liquid to eventually sink downwards, since there is no pressure gradient difference at the interface between the two liquids. The possibility of Brownian motion causing a transfer of molecules and the Rayleigh-Taylor instability were brought up as potential explanations. It was also mentioned that this system is a metastable phase and can be easily disrupted by perturbations or thermal fluctuations. The conversation then touched on the concept of the butterfly effect and the complexity of the system.
  • #1
Suni
13
0
Hi all

Just a quick (relatively simple) question..
As high school physics/chem tought, a liquid of lower density will float uopn that of a higher density. This makes sense in most situations because of the pressure gradient in the higher-density liquid pushing the other fluid upwards. But what if we had a situation as so:

A low density liquid is sitting in a beaker. We then somehow place a high density liquid PERFECTLY upon the lower density so there is a point in time where the beaker would look like:

High density liquid
----------------- INTERFACE
Low density liquid

Now my question is what is it that would force the higher density liquid downwards? Because none of the liquid has actually penetrated into the low-density area yet (due to the interface) we can't use any pressure gradient differences. I was thinking it may have to do with Brownian motion causing a transfer of molecules across the interface which would eventually cause a total realisation of the pressure gradient. Does this make sense or is it wrong?

Thanks,
Dan
 
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  • #3
Thanks for the link mate.. very helpful.. wasn't aware of that
So it is then right to say that a system like that can stay in equilibrium so long as it isn't touched/bumped etc? I guess that makes sense!
 
  • #4
Suni said:
Thanks for the link mate.. very helpful.. wasn't aware of that
So it is then right to say that a system like that can stay in equilibrium so long as it isn't touched/bumped etc? I guess that makes sense!
That's close, but not exactly right. The RT phase is a metastable phase, meaning that any perturbation will destroy it. However, it doen't need touching or bumping for this to happen. Ordinary thermal fluctuations at the ambient temperature will kill such a phase given enough time. The lifetime is hence inversely proportional to the ambient temperature.
 
  • #5
Salt domes to thunderstorms --- you don't really need the "liquid" constraint. This is also the situation in which "the butterfly effect" is manifested, the "butterflies" being the fluctuations G. mentions.
 
Last edited:
  • #6
OK that makes sense.. thanks very much guys
 
  • #7
so it's a complex system?
 

What is meant by "a liquid floating upon another"?

"A liquid floating upon another" refers to a phenomenon where two different liquids, such as oil and water, do not mix and instead form distinct layers on top of each other.

Why do some liquids float on top of others?

This is due to differences in density and polarity between the two liquids. The liquid with a higher density and/or stronger polarity will sink to the bottom, while the one with a lower density and/or weaker polarity will float on top.

Can any two liquids form distinct layers like this?

No, not all liquids can form distinct layers when mixed. Only liquids with different densities and polarities can exhibit this behavior.

Is the layering of liquids permanent?

No, the layers of liquids can be disrupted and mixed together through agitation or changes in temperature and pressure.

What practical applications does this phenomenon have?

The layering of liquids has various practical applications, such as in oil and water separation, in the production of food and beverages, and in chemical reactions where different layers are necessary for proper reactions to occur.

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