Assume two liquids of different density stacked on top of each other. Or, assume a ballon filled helium gas, in our atmosphere.
1. Why does the lighter fluid “go up”? How does this work out on a molecular level?
2. What would happen when these fluids in free fall, I.E not under the influence of gravity?
In: 8
Molecules in liquids (and gases) are, uh, wiggly, for lack of a better word. They wiggle around randomly and a given specific molecule will, over time, gradually move around the whole area that the fluid occupies. This phenomenon is called “brownian motion”. The reason that it happens is that no molecule is ever truly “still”. They have thermal energy, which causes them to vibrate a bit, and they’re constantly being hit and jostled by other particles. The momentum imparted to the molecule at any given moment is unpredictable but on average, they’ll just kind of move around randomly.
What this means for liquids of different densities is that they will gradually separate into layers. Brownian motion (and therefore mixing) is still happening, and the molecules are all moving around randomly, but on average the heavier ones will be drawn lower due to gravity.
In micro-gravity, this wouldn’t occur because gravity wouldn’t be affecting the molecules very much. The liquids would stay mixed.
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