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You know how when you fill a bucket with water and swing it around, the water stays inside?
What if we built a tube and filled it with water and spun it really fast?
The water would stay inside (with edges) and people could jump in (or be inside when it starts up, and then HEY PRESTO! A tubular
anti-gravitational spinning swimming pool that utilizes the force of gravity to keep you and the water inside.
If possible, make the outward acceleration no greater than the acceleration of gravity, because that's what swimmers are used to. - robinism
Exactly what I was thinking.
*NOTE* For the easily seasick: May be disorienting!
Spinning Bowl Swimming Pool
Spinning_20Bowl_20Swimming_20Pool
an awful lot like this [FarmerJohn, Feb 14 2005]
attacks "centrifugal force"
http://www.physicsc.../circles/U6L1d.html
[FarmerJohn, Feb 14 2005]
defends "centrifugal force"
http://www.physics2...rifugal_force.shtml
[FarmerJohn, Feb 14 2005]
Artificial-Gravity Swimming-Pool
http://www.spacefut...swimming_pool.shtml
Talks about the "gravity gradient" in a rotating system, and buoyancy changes in zero gravity. [robinism, Feb 14 2005]
Blue Champagne
http://www.varley.n...ne_Tod_Hamilton.jpg
[normzone, Feb 16 2005]
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Annotation:
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you mean like a giant hula hoop half
full of water spinning like the rings of
saturn? |
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like a washing machine with a clogged
drain on spin cycle? |
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like a tube that just forces water into
your lungs directly? |
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The same centripetal force (angular momentum?) that holds the water in the bucket would pull the people to the bottom of the bucket. If the water is deep, they drown. How about a wading pool?
Could you swing it more slowly - just fast enough to hold the water in, but no faster. If possible, make the outward acceleration no greater than the acceleration of gravity, because that's what swimmers are used to. And put salt in the water for extra buoyancy. Call the ride "The Undertow." |
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Obligatory [John Varley] "Blue Champagne" reference. |
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Even if you only read it once, it's a wonderful series of stories, and QM, the lifeguard, has been there, done that. |
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centrifugal adj. 1. Moving or directed away from a center or axis. |
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centripetal adj. 1. Moving or directed toward a center or axis. |
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Cool, so it's not centripetal force. But it's not centrifugal force either, since there is no such force. It's angular momentum, or something like that. |
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[FJ], Thanks for those two links; they made my head spin. I think you've got the right idea - continue to use the term "Centrifugal force", but always put it in quotes, so you have deniability. |
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[robinism] - it's centripetal force that acts on the swimmer and the water. |
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Consider a conker being swung round on a string. At a given point in time, it has speed and direction. For example, when it passes in front of the face of the person swinging it, it is moving left to right at, say, 30mph. If the string wasn't there, it'd head off in a straight line, left to right, and fall to the ground. |
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However, the string is there, so the conker swings round in a circle even though its natural tendency is to fly off in a straight line. This means that the string is providing a force acting on the conker to make its path bend. It's pulling the conker inwards to keep it in a circular path, and hence is centripetal as per [fj]'s definition. |
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When I was but a wee lad, I went camping on a school trip. For some reason we had a small pool with us, like a paddling pool about 1m high and 2m in diameter with semi-rigid walls. We realised that if we kept running round clockwise in the pool we could start a vortex so we decided to see if we make the vortex deep enough to expose the pool bottom at the centre. |
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The explosion when the pool walls finally gave way was quite spectacular. |
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I was taught in school that the water in the bucket thing was centrifugal force. School sucks. |
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//If possible, make the outward acceleration no greater than the acceleration of gravity, because that's what swimmers are used to. // |
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robnism, that is exactly what I mean. |
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Thank you for clarifying. |
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Under which circumstances, there would be two forces acting on the water; one outwards, one down. One is gravity, the other is centripetal force equal to gravity. The net force will then be 45 degrees downwards (or should that be at 45 degrees of depression?) and so the water will be perpendicular to that, ie slope at 45 degrees upwards. |
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This will only be true at one radius; at the centre there will be no outward force and the water will sit flat. Moving out will see higher rotational speeds, higher G forces and steeper slopes. The theoretical G force for a perfectly vertical wall of water is infinite. |
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So David, the overall downward force if the water surface is at 45 degrees is SQRT(2)G? That would be ok to swim in. |
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Yeah, that's right as far as I can tell. |
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That would actually be very cool to swim in, because you could be at the same level as your friend, but he's drowning and you're drinking a nice margarita. |
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Are we definately sure its centripetal and not centrifugal force, before I make a fool of myself when I ring up Mrs Mc Cluskey and read her the riot act? |
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If you made this really deep and gave the swimmers scuba diving stuff, this might work, and it might be kinda like being inside an underwater river, if you get what I mean... |
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[ether] the problem is not with the phrase 'centrifugal force', but instead how you think of it. There are two forces acting on a bucket twirling in a circle on a string; a- the force pulling the bucket in towards the center of the circle- called ‘centripetal force’; and b- the force pulling the bucket away from the center, which is in fact moving tangentially, instead of radially as most people picture it- which you can call 'centrifugal force' if it tickles your fancy.
It is the interaction of these two forces that keeps the bucket moving in a circle, and if either force were imaginary the bucket would move in a straight line. |
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back to the idea: If you spin the wall, and not the water, the water touching the wall will be moving faster then the water at the center (direct acceleration as opposed to indirect), this would occur in addition to the effect [d_s] was talking about, so the tube would need to be spinning pretty fast in order to be able to swim in the water, and even then most of the water will be mostly flat. |
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With a spinning bucket (let's assume that gravity and drag are not a factor), there is only one force acting on the bucket, and that is the tension applied to the string. |
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Since this force is towards the center of rotation (perfectly perpendicular to the instantaneous velocity vector), there is no tangential force, and thus the bucket neither speeds up nor slows down, but merely changes direction. This is "Centripetal force". Since any change in velocity, including a constant-speed change in direction, is called an "acceleration", we can refer to the effect of "Centripetal force" as "Centripetal acceleration", acceleration towards the center. |
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If we were standing in this bucket with no windows, we wouldn't be able to tell that we were spinning. We'd just feel a constant force pushing us towards the bottom of the bucket. If we dropped an object, it would appear to accelerate towards the bottom of the bucket. While the object is, in reality, just continuing on a straight path from the release point, to an observer within the bucket, it appears to accelerate, thus the term "Centrifugal acceleration". |
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Back to the centrifugal pool: If you were to swim in such a pool, you wouldn't feel any more or less buoyant than in a normal 1g pool. Just as the forces pulling you down are increased, so are the forces pulling the water down. Because of this, the equilibrium point (how deep you'll sink or float) is unchanged. |
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Mach's alternative: keep the pool still
(simplifies the plumbing) and spin the
rest of the universe around it. All
things being relative, the effect will be
the same. |
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Of course, Mach probably never actually
tried this. |
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"If you were to swim in such a pool, you wouldn't feel any more or less buoyant than in a normal 1g pool."
"The equilibrium point (how deep you'll sink or float) is unchanged." |
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Buoyancy does change with gravity. See link. |
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Suppose my equilibrium point is the pool bottom at 1g, and it takes me 1 unit of work to swim from my equilbriium point to the surface. At 2g, my equilibrium point is again the pool bottom, but I would guess that the work required to swim to the surface would be greater than 1 unit. (?) |
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First centripetal force would be the tube forcing you to travel in a circle. |
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>>It's angular momentum, or something like that.>> |
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more like linear momentum being acted upon.
And yes the Buoyancy might allow you to float, but the pressure Gradient is greater, so don't swim too deep. |
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I think it's like, totally tubular to the max. |
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acceleration of gravity ?? how fast does gravity go?? |
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The acceleration of gravity is a common term meaning the acceleration caused by gravity. The value depends on where you are. On the surface of the Earth, it's about 10 meters per second per second. So the velocity of a falling object increases by 10 meters per second, each second. |
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[robinism] Your link annotation is incorrect - there is no zero-gravity. Anywhere. There is "freefall" (apologies to [Freefall]), but that isn't the same thing.
I'm with [Freefall]'s assessment of Archimedes' principle - the upthrust is equal to the weight of water displaced - the weight would be increased because of the acceleration, and so the upthrust would increase to compensate.
[brodie] conker = horse chestnut. In the UK, these are pierced and attatched to strings (pros use leather bootlaces) and are used in the eponymous game. |
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That must be why the authors put "Zero gravity" in quotes, and why people refer to "Microgravity" instead of "Zero Gravity." Vocabulary aside, the article does say that bouyancy goes away in microgravity. |
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I originally pictured this ride like a centrifuge. That's why I pictured people who tend to sink (like me) getting stuck at the bottom, like heavy particles in a centrifuge. I see now that it takes more than increased gravity to do that. But whatever it does take to centrifuge out particles, (gravity gradient? no water at the bottom?) [df] would need to find out, and make sure it doesn't happen on his ride. |
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<aside>No bouyancy - no convection, so my lava lamp would be useless on the ISS. |
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Right, I'm confused. What axis is this pool spinning about? Is it spinning like a roundabout at a fairground, ie the axis is vertical? Or is it more like the London Eye, with a horizontal axis? |
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If it's like a roundabout, then the lateral G-forces experienced will increase as you move from the centre of the pool to the edge, so the water will be flat in the middle and sloped at the edges. If it's like the London Eye, then I don't think this can work. The problem is the viscosity of water is very low, so spinning the walls of the pool won't automatically make the water spin with it. Instead, you'd get water tumbling over and over, staying at the bottom of the "wheel". To get the water to stick to the walls, you'd have to spin it extremely fast, and this would _not_ be comfortable for swimmers. It would, in fact, be more like riding inside a washing machine. |
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The trick where you swing a bucket upside down only works because the back wall of the bucket follows behind the body of water, pushing it along and forcing the water to move round at the same speed as the bucket (Does that make any sense? I'm stuck without being able to wave my hands and draw pictures, I'm afraid). It's fundamentally different to the swimming pool, where the water isn't pushed by anything, but dragged by contact with the pool bottom. In the bucket, the water must move at the same speed as the bucket; in the pool, it doesn't have to. Consequently it is much harder to get the water to spin fast enough to loop-the-loop, and even when this is achieved, the flow will be very turbulent and possibly dangerous. |
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So, I phoned up and tried to speak to my former science teacher Mrs Mc Cluskey, her of the swinging bucket. She still teaches in my old school. I said to her, 'Hey you, you told me that swinging bucket thing with the water in was all about centrifugal force when *actually* it was just as much about centripetal force.' |
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She replied: 'Who is this?' |
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I explained that I was a former pupil and that I had just learnt that not only had she decieved me, but had been decieving gullable, hormonally challenged, spot ridden kids for decades. |
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She replied; 'Fuck off.' And put the phone down. |
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Old people can be so cruel. |
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Call your former English teacher about teaching you the "e" before "i" but not after "c" rule. |
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the rule changes when it comes before gullable. |
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Granted, in "zero gravity", there is no buoyancy. I'm not talking about magnitude of buoyant force, I'm talking about equilibrium position in the presence of a buoyant force. |
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If an object is floating on the surface of a liquid, the g-force applied (assuming a uniform g field) is irrelevant, since it is applied to the liquid too. The increase in upward buoyant force applied to the object will exactly cancel the increased downward force applied by gravity. |
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In a rotating environment, the force is not constant. Closer to the axis, the force is less than the force farther from the axis. In a large environment (a person in a swiming pool) this won't be very significant. In a small environment (a person in a washing machine) it will be significant. Assuming we're not swimming in a washing machine, the difference is insignificant. |
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//With a spinning bucket (let's assume that gravity and drag are not a factor), there is only one force acting on the bucket, and that is the tension applied to the string//
If this is taken as true, then according to you [Freefall], every bucket hanging from a string should be spinning. |
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[Freefall], you are assuming that the riders are floating. But some riders will sink. Their "equilibrium position" is the bottom of the pool. |
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Centrifuges increase the sedimentation of particles somehow. Yet everyone seems to agree that this ride will not increase the sedimentation of humans. I accept this, yet I wonder, what is the "difference that makes a difference" between this ride and a centrifuge. The other issues are pretty much cleared up, to me. |
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//Centrifuges increase the sedimentation of particles somehow. Yet everyone seems to agree that this ride will not increase the sedimentation of humans. I accept this, yet I wonder, what is the "difference that makes a difference" between this ride and a centrifuge.// |
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It's just the magnitude of forces. Particles in suspension, if more dense than water, will be pulled to the bottom in a centrifuge. Inside a centrifuge is a lot like being in a strong gravitational field. If something's a little bit heavier than the water, it will sink quickly. Of course, if something's a little bit lighter than the water it will rise quickly. That's us, hopefully. |
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So the greater gravity increases the speed of buoyancy effects, but not the ultimate position? |
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If that's so, it does seem significant for safety, especially for swimmers who are slightly negatively buoyant. They are accustomed to being able to keep their heads above water by working, but the increased gravity will pull them down faster, and force them to work harder, no? |
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(I appreciate that you keep answering these questions, you all. Stop at anytime!:-) |
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If buoyant then we'd be very buoyant. If negatively buoyant, well - you wouldn't want that. A life vest should help the negatively buoyant, I'd think. |
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It would be fun (up to a point) to spin this thing faster, up to a few G's. The positively buoyant (and those with life vests) would float high on the water. |
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Can I go back to when I was 14 please?. I understood the world a lot better then. So did most of you by the looks of things! |
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My Apologies, [robinism], you are right. I understood this *concept* much better when I was 14. At that time, it was the world. |
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High in the water, [Worldgineer]? Are you sure? Because [freefall] and [Absenthe] have already convinced me that the "equilibrium point" doesn't change with gravity. |
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No, I'm not sure - it just seemed right. Let's see. A floating object will displace enough water to equal it's weight. Now, if we double the object's apparent weight. And if we double the weight of the water. Yep, the equilibrium point shouldn't change. |
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[Brodie], no, not all buckets hanging from strings would be spinning. I was trying to convey a situation in which there was only a radial component of force applied, so that the bucket was not speeding up or slowing down, but merely spinning at a constant rate. |
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OK, I concede. For those who are naturally heavier than water, there may be a problem. These people may want to wear floatation devices. |
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So Spinning the tube won't work... What about forcing the flow of the water? Put paddle wheels in the bottom of the tube. Add sauna jets, whatever. If you can get the water moving fast enough, you might not even need to move the tube. I think somewhere there's a water slide that actually does a loop. |
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However, if you're putting in paddles, jets et cetera, you're accelerating only part of the body of water (the paddles, for example, would only accelerate the bottom part of the pool, where the paddles themselves were). Having a speed differential will cause vortices - and an undertow. |
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And What it the point of this idea? |
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smimming pools already are sort of anti-gravitational, thats what NASA uses to train their astronaughts for space walks. |
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What about the diving board? If it extended to the center of the rotation, you dont know what direction you would fall if you fell at all. |
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So, what if we used like an inside-out paddle wheel? Like the ones on steam boats and mills? That would keep the water turning , and then, once it got up to speed, have it be really nifty and retract the paddles, so that its a clear swim for any involved. Also, unless the swimmer were really fast (like olympic fast, or at least my level- which is damn fast), wouldn't this be a stationary pool? For fast people, I am fairly sure that they would eventually work their way up the side, go around the top, and then come back down. Or maybe I'm imagining this wrong. |
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Marked for tagline: [Or maybe I'm imagining this wrong]. |
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I really can't see the point of this idea. Bone |
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You'd have to get Steven Wright to be the lifeguard. |
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You cannot force the people to turn. That is impossible. Instead, only try to realize the truth: There is no force. Only the mind turns. |
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It would seem like it would be great fun until
someone loses an eye. |
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I suspect that you would have a greater tendency to sink in a rotating body of water, for two reasons: |
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1) Most people's legs are denser than the rest of their body (more bone and muscle, less fat and air). Since the legs tend to be lower in the water / further from the axis of rotation, they experience greater acceleration; your sinky bits become disproportionately more sinky. A hydrometer gives consistent readings over a range of gravity or linear acceleration, but reports a lower density in a rotating system. |
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2) The increased pressure gradient would make it harder to inflate your lungs, and would compress the air in them when you hold your breath. |
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But, averaged over the course of one revolution, you won't have to put any more effort into breathing and your legs won't sink any more than it would in the same time period in a stationary pool: based on 2g at the bottom and 0g at the top. |
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On the Centripetal/Centrifugal force thing, if you
look at the system in a rotating reference frame,
you do find a centrifugal term. |
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In a stationary frame it's purely centripetal, since
the primary force is the one that keeps the
bucket from moving tangentially in a straight line
(although, even in a stationary frame, the
reaction force on the rope can be described as
centrifugal, just not mathematically). |
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As far as buoyancy, yeah, if a person is (net)
positively or neutrally buoyant, they'd be fine,
except if the radius is small enough that tidal
forces come into play as [spider] describes such
that their legs pull them down. If someone is
negatively buoyant (which paradoxically includes
most serious swimmers, lean muscle sinks), they
are going to have to work harder to stay afloat. |
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Contrary to [David_Scotherm]'s comment, it would
be possible for this to work with a horizontal
(Ferris Wheel) axis, although it would have to be
spun somewhat faster than needed to provide 1g
to prevent people from falling out by swimming
the wrong way. The reason for this is that if all
walls are spinning, there is nothing but inertia to
prevent the water from moving at the same
speed. Thus if you start with the tube empty,
spin it up to speed, then add a little bit of water,
that water will come up to speed very quickly.
Add a little bit more, and likewise. Even when it
gets full, the water near the center is only
interacting with water nearer the edges, which is
interacting only with the walls, so no reason for
the water to slow. You probably would want
rough (paddle-ish) walls to prevent currents from
everyone swimming the wrong way or similar, but
it's not impossible. |
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what is the minimum speed of the water that will keep it from falling at the point where the gravitational force is 1g? (some research needed on my part). What about the swimmer? if the swimmer swam in the other direction would they not begin to fall out of the loop? and if they swam in the other direction would they not "sink" to the bottom? with each loop would not the individual experience a 2G shift between the top of the loop and the bottom? Oh wait, this isn't a vertical pool. well, I'm deeply disappointed. (wanders off bored) |
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Also, unless you have some significant buoyancy aids you will sink like a rock and drown, something to keep in mind. Buoyancy is not uniform with force, or a centrifuge would be a total waste of time. |
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[WCW] Read above. Buoyancy is uniform with
gravity, you can't centrifuge something that is
neutrally buoyant. |
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However, there are very few mixtures where the
components
are neutrally buoyant with each other, which is why
they work. |
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If the ring has baffles in it, the water would quickly
reach the same speed as the "pool." |
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This could actually work, although I doubt it would be
practical or profitable (so, government project?) thus
I'm going to give it a bun. |
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parts of me are more dense than water. When pressure is applied to the softer bits of me, gasses inside me compress and my density falls below the density of water and I sink. The fact that the water is incompressible does not mean that my body is similar. a compressible object of neutral buoyancy will be compressed in centrifugation and fall to the bottom.
true fact. |
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The majority of your body (except the lungs and
eardrums) is just as incompressible as water, since
it is dirty water. Again, this was discussed
significantly above. |
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Some people are naturally buoyant, even when
completely exhaled. These people will still float.
Some people are naturally denser than water,
these people will have to work slightly harder to
stay afloat. Since this tends to correlate with
fitness, it should still be doable (un-atheltic
skinny types might be prone to drowning, but
they've got it coming). |
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It's probable you won't want the pool to be deep
enough to cause problems, but if a normal person
can swim to the bottom of a normal 12 foot pool
without trouble (well, my ears popped), doubling
the pressure should still allow plenty of room for
swimming. |
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Heck, if you're really worried about it, just use highly
saline water in the pool. That will make flotation
even easier under high g, since every bit of the body
will be less dense than the water. And 2-3g won't
centrifuge salt out of water. |
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If the ring spins to produce a 1G centripetal force,
the resultant force would be 1.414G. |
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Now for the fun bit: RE = œmv² |
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Therefore it's going to take more effort to move water forwards and backwards (applying delta-v's) than sidewards. It's going to take more effort to move yourself forwards or backwards as well. |
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It would still be entertaining to see someone try this.
Especially when the lifeguard says "everybody out of
the pool!" |
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[whlant] I'm stil playing with the ferris wheel design,
not the merry go round. Either is feasible. |
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// "everybody out of the pool !" // |
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The wheel stops; the water and occupants continue to spin, spewing out an opened hatch. |
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The ferris wheel design would be more challenging. I
think the merry-go-round concept is more feasible,
and probably safer. |
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Fat, my friends, is compressible. |
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[WCW] please cite a source for that claim. Fat is
manipulable/shiftable, but it is not particularly
compressible to the best of my knowledge. Not
more than water or oil, which is essentially what it is
made of. |
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[+] how the hell did this deserve all those bones ? |
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//[+] how the hell did this deserve all those bones
?// |
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I can only assume it has something to do with an
irrational fear of wet roundish spinning things. |
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The Danish Walrus Ballet is a highly regarded artistic troupe. |
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So... basically swim in a giant toilet bowl. Sounds like fun. |
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