True, but:
a)aren’t we working around/ignoring the pressure factor? (otherwise, the answer to the question “What’s it like to swim on Europa” is simply “lethal”)
and
b)I don’t think that’s what the_diego was talking about (I’m not sure what it was, but it doesn’t look like that).
Europa, no. But Titan yes.
“In fact, humans on Titan could fly by muscle power. A human in a hang glider could comfortably take off and cruise around powered by oversized swim-flipper boots—or even take off by flapping artificial wings. The power requirements are minimal—it would probably take no more effort than walking.”
the weather is a bit nipply, though.
The relative densities would not change. Say, on Earth, you float up to your ears and a 1kg lead sinker makes you exactly neutrally buoyant. Then on any planet you would float up to your ears and the same sinker would make you neutrally buoyant.
But if you were to swim (without the sinker) on a high-gravity planet you would find it would take more energy to submerge yourself. When you push yourself under you are essentially lifting up a volume of water. The higher the gravity the more energy you need to lift that same volume of water.
Okay, I’m coming at this from a slightly different angle and you guys seem physics inclined. Imagine a Elysium style space station ring, in which there is a lake, on which there is a boat.
Question 1) When the ring spins at slow, medium and fast angular velocities (ie different centripetal accelerations), how does the boat sit in the water? a) the same height for all three, b) higher when spinning faster c) lower when spinning faster.
Question 2) As the ring angular velocity increases (centripetal acceleration increasing), the boat a) stays at the same height, b) rises to a new height, c) rises during acceleration, but falls back to the original height once the angular velocity becomes constant, d) falls to a new low, e) falls during acceleration, but rises back to the original height once the angular velocity becomes constant.
Thanks for your help. FYI This is actually relevant to a proposal I’m going to make.
A centrifuge separates by relative density, doesn’t it? It only speeds up what would happen anyway, that is, denser stuff sinks to the bottom and vice versa.
But would I crystallize in the same way under high G?
In theory, it should sit at the same level all the time - because the weight of the boat, and the weight of the water it displaces both increase or decrease in proportion to the force of (real or fake) gravity.
If you’re just launching the boat, it will settle to its floating position quicker under higher gravity (and sinking objects will sink faster, and floating objects will rise faster).
Yes, as agreed in post #15. Dynamic systems will speed up. Static systems will not be affected.
The centrifuge does increase the rate of separation, but it can also cause it to occur where it would not occur without.
eg small particles may stay in suspension, eg due to their stickiness. The artificial gravity of the centrifuge can overcome the stickiness to make the particles drop.
I imagine there are a few boundaries that change - gels become fluids in a higher gravity environment - or in a lower gravity environment, things we know as fluids start to act more like gels (I’m not actually sure if I want to include the surface tension behaviour of water in microgravity in this category or not)
I thought Brownian motion kept particles in suspension.
Exactly so; if your boat is pushed deeper than the equilibrium point, then the restoring force is dependent on the excess weight of the displaced water, and acts on the mass of the boat. One of these is affected by gravity and the other is not. At equilibrium, the weights of the boat and displaced water balance out, as long as they are non-zero (which is why you require some gravity).
I think you have invented a new and useful word:
Nipply - adjective (nipplyer, nipplyest)
informal
of the weather - very chilly:
it’s a bit nipply this morning (as in it makes ones nipples stand out)
For a certain range of conditions, it probably does, but Brownian Motion is just lots of little random, but finite forces - if the particles are too big/heavy, the forces will be insufficient to keep them suspended - but ‘heavy’ here is dependent on the force of gravity - in lower gravity, larger particles will be able to stay suspended.
That makes sense. Thank you.
If you’re getting your gravity from centrifugal force, and you’re changing the rate of rotation, then you’re going to get complications from the tangential acceleration, as well. In layman’s terms, it’ll slosh.
Do it gradually enough that you minimize the sloshing, though, and the boat will just sit there at a constant height.
Centrifugal gravity raises an interesting question, though. If in zero-G you have a cylinder containing some amount of air and water (say, half and half, at STP), when you spin the cylinder, what happens? I mean, water near the wall will cling to the wall, but water near the center will not be inclined to move outward, at least initially, and air near the sides will not tend to be forced inward. Has anyone experimented with this? Assuming a single axis of ritation, would such a cylinder eventually reach some sort of equilibrium with a layer of water at the wall (forming by surface-tension capture of water near the wall) with air toward the inside (like a bubble) and some globs of water in the middle? Would air moving inward eventually force water in the middle outward or to the end (where it would be flung outward)? And how would the smoothness of the inner surface affect the distribution of contents?
Even though there’s an equilibrium for heavy material at the center, it’s an unstable equilibrium. Eventually (which in practice wouldn’t be a very long time), you’d have all the water on the outside, and all the air in the middle.
Eventually, everything will rotate - because each of the layers is in contact with the next - even though they’re fluids, they are touching one another and will transfer forces.
Think of it this way:
Put a large bowl of water on a record player turntable and turn it on. At first, only the bowl rotates - the fluid stays as it is, but gradually (and beginning from the layers most closely in contact with the bowl, but eventually extending throughout the entire body of the fluid), it all starts to rotate, until eventually, everything is rotating at the same rate - and the fluid is piled up toward the edges of the bowl.