Thread: g-force applied to object submerged in liquid

hi all need a fue answers for a idea i had
A sealed vessel for eg. spherical, is filled to capacity with liquid and a solid odject of the same density is suspended in the liquid then accelerated

is that object inside the vessel going to be immune to the g_force applied to the vessel because it is of the same density or will the object inside the vessel be subject to the applied g-force from the acceleration


my idea is transportation of the human body of over and above the currant max acceleration and g-force sustainable for long periods of time


liquid high salt content water
calibrated to each persons currant density by micro airating the water till the person was mid suspended in the liquid or in balance with the liquid as i like to call it

The person in the tank of water will experience the same g force as somebody who is not immersed in water. I don't know if the water would help to distribute the force or not.
G-suits have been developed for fighter pilots. These work mainly to prevent blackout by putting pressure on the legs and abdomen to keep the blood from pooling in the lower body.

http://en.wikipedia.org/wiki/G-suit

Originally Posted by hayabusajay

hi all need a fue answers for a idea i had
A sealed vessel for eg. spherical, is filled to capacity with liquid and a solid odject of the same density is suspended in the liquid then accelerated

is that object inside the vessel going to be immune to the g_force applied to the vessel because it is of the same density or will the object inside the vessel be subject to the applied g-force from the acceleration


my idea is transportation of the human body of over and above the currant max acceleration and g-force sustainable for long periods of time


liquid high salt content water
calibrated to each persons currant density by micro airating the water till the person was mid suspended in the liquid or in balance with the liquid as i like to call it

Welcome to The Science Forum :-D

An astronaut suspended in a liquid on the surface of the Earth (1 g) does so by virtue of the fact that the difference in pressure of the liquid pushing up from below his body and the pressure of the liquid pressing down from above his body exactly counteracts the pull of gravity. This difference in pressure is directly related to the density of the liquid - if the liquid is more dense, the difference in pressure is greater and the astronaut will float to the top.

If the vessel is subjected to an acceleration of 2 g (in space), the solid walls of the vessel confine the liquid and force it to accelerate at the same rate. The astronaut is not so constrained by a solid surface, however. Inertia will cause him to drift to the "back" of the vessel. He will, in effect, "sink to the bottom".

This is so because the density of the liquid doesn't change (it's not compressible). The difference in pressure that was sufficient to keep him suspended against a gravitational force of 1 g is not great enough to keep him suspended against a pseudo-gravitational force (an acceleration) of 2 g.

This is not unlike an astronaut "floating" in an ordinary spaceship at 0 g. When the spaceship is accelerated, everything that's not attached to the ship's structure will drift to the back of the spaceship.

Chris

Originally Posted by CSMYTH3025

This is not unlike an astronaut "floating" in an ordinary spaceship at 0 g. When the spaceship is accelerated, everything that's not attached to the ship's structure will drift to the back of the spaceship.

Chris

Let's look at this from an inertial reference frame. The ship is in deep space (so no external gravitational field) and accelerating with an acceleration . The fluid, being constrained by the container, and assumed to be incompressible also accelerates at The astronaut is somewhere within the fluid body, and the acceleration of the astronsut is unknown. Since the astronaut is in contact with nothing but the fluid, and there is no gravitational body force, all forces on the astronaut ae applied by the fluid.

At this point the force on the astronaut is the usual bouyant force where V is the displaced fluid volume and is the mass density of the fluid. So, the net force on the astronaut is in the directiom of acceleration of the ship. The astronaut is therefore accelerating at the rate where . If the astronaut is completely immersed . From this we see that . From this we see that, relative to the ship the astronaut will "float" if , maintain position if
and "sink" if

wow didnt thing id get a responce thanks for that it dose help

It's an interesting question because one wouldn't intuitively expect the "floating" body to remain in position relative to the container if the container accelerates - however, I accept DrRocket's conclusion that this would happen if the densities of the body and the surrounding fluid were the same.

Originally Posted by Old Fool

It's an interesting question because one wouldn't intuitively expect the "floating" body to remain in position relative to the container if the container accelerates - however, I accept DrRocket's conclusion that this would happen if the densities of the body and the surrounding fluid were the same.

Thanks DrRocket for correcting my intuitive mistake (translation: uninformed guess) in my earlier post. I forgot to take into account the increased uniform pressure (the increased "weight") of the fluid at higher accelerations. Your explanation makes this obvious. Very embarasing - my appologies

As pointed out by Harold14370, the astronaut would still feel the same acceleration that he would feel sitting in the pilot's chair of an ordinary spaceship undergoing acceleration. Thus, being suspended in water wont help the astronaut withstand high g-forces.

Chris

Originally Posted by CSMYTH3025

As pointed out by Harold14370, the astronaut would still feel the same acceleration that he would feel sitting in the pilot's chair of an ordinary spaceship undergoing acceleration. Thus, being suspended in water wont help the astronaut withstand high g-forces.

Chris

But it will help withstand the g-forces, pretty much in the way Harold alluded.

It will not change the net/average force on the astronaut or the acceleration of he astronaut. But because the force is uniformly distributed as a hydraulic pressure it will reduce the peak in the force distribution, which should reduce discomfort.

With a solid body it would help, however the human body is not solid nor do the organs inside it have the same density. Heart, liver, bones, blood all have different densities and would react differently to the acceleration. In this situation you are looking at a capsule within a capsule. The human is a capsule of organs within the capsule of the space craft.

Originally Posted by Darkhorse

With a solid body it would help, however the human body is not solid nor do the organs inside it have the same density. Heart, liver, bones, blood all have different densities and would react differently to the acceleration. In this situation you are looking at a capsule within a capsule. The human is a capsule of organs within the capsule of the space craft.

True, but distributing the load to reduce peak force on the exterior of the body will reduce discomfort, just as I said.

If you don't believe that, try sitting on a tack.

So if one were suspended in a breathable liquid that is the same density of one's blood (assuming that's even possible for discussion's sake) it could reduce the blackout effect, but would still feel pressure on denser parts of the body? I'm thinking bones and dense muscle tissue.



On a side note, I would love to see them play with this on Mythbusters.

I am not so sure that you would be discomfort free. You are distributing the load however the load still exists. On parts of the body that have less density that load would increase. I imagine that you would still feel like something very heavy was sitting on your chest since your lungs would still need to be filled with air and that would could possibly result in death. Theoretically liquid breathing could mitigate this by filling the lungs with a PFC liquid, however full liquid ventilation is not yet a reality in humans.

Other organs could also be affected by the forces at work, though like you say you may not feel discomfort, at least until it is too late.
http://en.wikipedia.org/wiki/Traumatic_aortic_rupture

Originally Posted by Darkhorse

I am not so sure that you would be discomfort free. You are distributing the load however the load still exists. On parts of the body that have less density that load would increase. I imagine that you would still feel like something very heavy was sitting on your chest since your lungs would still need to be filled with air and that would could possibly result in death. Theoretically liquid breathing could mitigate this by filling the lungs with a PFC liquid, however full liquid ventilation is not yet a reality in humans.

Other organs could also be affected by the forces at work, though like you say you may not feel discomfort, at least until it is too late.
http://en.wikipedia.org/wiki/Traumatic_aortic_rupture

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