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.
I’ll give it a shot.
Best way I found to understand it was by imagining the molecules as being hyperactive when at higher (relative) temperatures. When someone is crazy and bouncing around off everything, you need to give them more space.
So (generally) the density goes down as the energy levels go up. Water is strange, it’s most dense at 4 degrees C, and it’s solid state is less dense than it’s fluid state, but I digress.
So that’s independent of gravity. Under gravity, fluids/gasses with greater density, experience higher gravitational pull than less dense fluids or gasses, that’s why they “go up” relative to less energetic matter. (Ignoring diffusion)
If we were in microgravity, then the fluid with the highest density would be pulled into the middle of the floating sphere and the less dense ones would be on the exterior. For example if we had a huge amount of oil and water in space, the oil would surround the water in these conditions due to its lower density relative to water.
Edit : Amounts of oil and water in microgravity must be very large to exert any significant gravitational forces to separate based on density.
Denser liquid = more mass per volume, = gravity pulls it down harder than the less dense liquid. Same reason a rock sinks in water. On a molecular level, molecules might be closer together on average, or just bigger individually
Think about dropping a rock in water. The rock sinks because it is heavier. Density is just weight/volume. A heavier liquid/gas/object will literally sink.
Latest Answers