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I Swimming in different gravities

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  1. Nov 20, 2016 #1
    Is swimming affected by gravity? How will swimming in micro gravity compare to high gravity and low gravity.
     
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  3. Nov 20, 2016 #2

    phinds

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    Swimming in micro gravity seems a sure way to drown. Do you see why?
     
  4. Nov 20, 2016 #3
    Because water stick to surfaces making it very hard to escape the water surrounding you? Like the Canadian astronaut pouring water on his eyes to simulate crying in space.
     
  5. Nov 20, 2016 #4

    phinds

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    No, because water goes EVERYWHERE in micro gravity and only very slowly settles back. That means if you were in a swimming pool in microgravity you would soon be "swimming" in a solid mass of combined air/water droplets and could not avoid breathing enough water to kill you.
     
  6. Nov 20, 2016 #5
    Sounds like a bad way to go. Thanks for explaining.
     
  7. Nov 23, 2016 #6
    I think water is too sticky to have a bunch of water droplets unless you were frantically stirring the water-air interface (perhaps because you were drowning). It would tend to clump into big balls around you, kind of like how water stuck to the washtowel and couldn't be wrung out. For a small amount of water, you could shake it off and it would form droplets and go to the sides of the vessel. But for a pool of water, shaped as a giant bubble, I think the shaking energy would be quickly dampened by the water, unless you were at the surface, where you could create a bunch of spray. You could probably swim to the surface of the bubble, but unfortunately, the bubble will have a tendency to try to recenter around you. I think a person could out-swim this tendency and reach the edge. But then when they tried to poke their head out, a small mass of water will stay adhered around the head, causing breathing problems. They'd have to shake the water off and clear their faces with their hands to breathe. And they'd have to do this fairly quickly before the water ball re-absorbed them. But, my uninformed guess is that it is survivable. Another challenge is knowing which way to go. It's hard to see in the water, and you will have no sense of which way is toward the surface.

    Now, in microgravity, you can just swim in air, so breathing isn't an issue. Accelerating is slow though, since air isn't very dense.

    I don't think much changes at higher gravity from normal swimming, unless you go to extremes. It might be easier to float, due to positive buoyancy , but a bit harder to get above the surface of the water for something like a butterfly.
     
  8. Nov 23, 2016 #7
    Ok, forget microgravity. Let's talk about half gravity or double gravity.

    First the buoyant force. Bouancy is proportional to the weight of the water displaced, but since we are varying gravity and weight we should probably expand on that a little in terms of density.

    Weight of displaced water
    W = V * density * g = m g

    Increase g on both sides of the equation and the volume of displaced water does not change. You will float the same. However the higher gravity will compress the water making the density higher, so you will float higher. However water is pretty incompressible. In fact, YOU are much more compressible than water (at least until your lungs collapse) so it will take more of your body to fill that V on the left side so actually you will float lower (and will have trouble breathing!)

    Floating isn't all there is to swimming. In fact, unless you are on your back, you float too low. So we tread water. We swim to apply a constant upward thrust to equal m g h of staying h higher than we would normally float. If we increase g we increase the upward force required to tread water. The difficulty of treading water increases linearly with gravity. Might it be more easy to do because the water is more dense? Or because the water is heavier? It isn't much more dense, and as to how much thrust you can achieve pushing aside water, you didn't change its mass, and you didn't change the generated impulse. In fact, it is doubly more difficult because your hands an arms are heavy.

    We could move on to swimming, but I think that more or less covers it.
     
  9. Nov 23, 2016 #8
    You aren't really more compressible. At higher pressures, you simply take more air into your lungs to fill the same volume. Now, this can potentially cause problems with oxygen poisoning if the atmospheric ratios aren't right, so you probably want an atmosphere with lower oxygen percentage at higher pressures. Higher gravity doesn't necessarily mean higher pressure-- it depends on the thickness of the atmosphere. Divers can experience much higher pressures without lung collapse.
     
  10. Nov 23, 2016 #9

    Nugatory

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    Actually you are (or at least I am). Even after a full exhalation, there's a fair amount of air in the lungs and that air is just as wonderfully compressible as any other gas. The volume of the chest depends on the pressure of the air inside at least as much as the mechanical rigidity of the rib cage (which isn't very rigid at all, or we couldn't breath).Thus, as pressure increases the human body loses volume much more quickly than an equivalent volume of liquid. Two observations:
    - Even with lungs are full of air, there is a water depth at which the human body sinks instead of floating. In 1G that's usually a few tens of meters, and is one of the reasons that escaping from a sinking ship is so difficult.
    - SCUBA apparatus wouldn't work without a pressure regulator that puts compressed air into the lungs to balance the pressure of the water outside. You can't just take more air into your lungs on your own, you need additional pressure to offset the compressibility of the chest cavity.
     
  11. Nov 23, 2016 #10
    With SCUBA, you have a rigid contained air source, so the air source pressure is independent of the water pressure, so you need pressure regulation. However, your point does translate into other swimming.
    It will be much harder to snorkel at higher gravity because of the difference between the air pressure and water pressure. This, of course, scales with the length of the snorkel. Also, normally, we swim with our lungs slightly below our head. This creates a snorkel effect in our esophagus. It probably won't make much difference if you are swimming horizontally like in a freestyle, but if you are upright treading water it will be somewhat harder to breathe.
     
  12. Nov 23, 2016 #11
    When I said this I had two things in mind. First I was aware of what Nugatory mentioned about divers ceasing to float at a certain depth due to being compressed. I admit that is a higher pressure increase than we are talking about here, about 3 extra atmospheres instead of one, but in any case I think it makes it hard to argue which direction the sign goes. At higher pressure you compress faster than water and become less bouyant not more. However, I also have to admit to not thinking about it too hard and half basing my statement on the knowledge that water just isn't very compressible.
     
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