The circulatory gets a *lot* of help from muscular artery walls, muscles that control venous volume, systemic muscles, and a lot of one-way valves.3dent:
What is the effect on gravity underwater?
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R
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3dent:
Seems to me the difference is a function of friction, not the ambient pressure difference. If you take a short U-shaped tube and fill it close to the top with water, the water levels will balance. If you blow in one end of the tube the water will rise in the other end to compensate for the pressure difference. Changing the length of the tube may slow the balancing as a result of resistance to the water flow, but balance will still be acheived. So that 2.32 psi overpressure has to be balanced. Either blood is going to have to pool somewhere or it will have to flow thru the pump return channels.
jonnythan:Someone reads TSS
Now if your heart stopped pumping while you were vertical underwater, the same thing would *not* happen. The blood would stay right where it is. This is because, although the absolute pressure in the circulatory system is much higher at the feet than the head, the ambient water pressure COUNTERACTING that pressure is equal to it, whereas on land the air pressure is negligible.
Perhaps, but I doubt it. I'd expect the blood in a body suspended in one position in the water for several hours to collect at the lowest point.
jonnythan:
Why do you think so?
jonnythan:
What evidence do you have to supprt this?
jonnythan:
I will give it a try.
jonnythan:
A body isn't a ziplock bag and blood isn't colored water.
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Gravity works under water in exactly the same way it does out of water.
However, the physical properties of individual objects or things may cause them to behave in a different manner because they are submerged.
However, the physical properties of individual objects or things may cause them to behave in a different manner because they are submerged.
rab
Contributor
I'm surprised that with all the talk of circulation, that no one has mentioned immersion diuresis. Partly from cold, but also from the change from blood tending to "pool" in the lower extremenies (aka, "legs") to being more evenly distributed throughout the body (yup, it's just like the Ziploc bag analogy).
-Rob
-Rob
rab:
No, it does not say that. It is temperature driven. "Immersion, along with a water temperature that is colder than air, causes narrowing of the blood vessels....".
If the water was warmer than you are, what would happen? I do not think the Ziploc bag theory applies in this case.
Back to the point.
Look, the acceleration of mass aka gravity, is the same underwater or above water, providing the mass of the object, and distance from the object, ie. earth, remain the same. you are confusing the mitigating factor of the bouyant force with negating gravity. It just looks that way.
I suspect that if it (immersion) negated the gravitational force there would be some sticky issues with time as well. So much for relativity.
What about all those exhaled bubbles that will just collect around your head. With no gravity, they won't really feel the urge to go anywhere. Pretty soon, you won't be diving in water, you'll be in a large-bubble foam. :11:
I am going along with Walter on this one (at least as far as I can discern from his post).
Gravity is just as strong under water as it is above water. The difference under the water is that the water is attempting to bouy you up toward the surface. In that case, it is actually strong enough to limit or prevent gravity from causing you to sink. Yet, that force is still there in equal strength.
Let's put this another way. When you are in outer space, there is less or no gravity depending on where you are in relation to planets that exhert gravitational forces. (Please, no long lectures on the properties of gravity in space. I am not a space expert but we all get what I mean here.) When you are under water, the full force of gravity is still there. However, the water counteracts it by your relative bouyancy.
In space, you are dealing with a lessening or an absence of gravity. Under water, bouyancy is counteracting it. The result is the same but the cause is not.
When you are in space, no matter which way you turn, blood will not go rushing to your head any more than when you are in any other position. If you turn upside down under water, you still feel the blood rushing to your head. Why? Because, even though you are relatively neutral in the water, the force of gravity is still there.
If you die underwater, I also suspect that blood will eventually pool in lower areas.
Gravity is just as strong under water as it is above water. The difference under the water is that the water is attempting to bouy you up toward the surface. In that case, it is actually strong enough to limit or prevent gravity from causing you to sink. Yet, that force is still there in equal strength.
Let's put this another way. When you are in outer space, there is less or no gravity depending on where you are in relation to planets that exhert gravitational forces. (Please, no long lectures on the properties of gravity in space. I am not a space expert but we all get what I mean here.) When you are under water, the full force of gravity is still there. However, the water counteracts it by your relative bouyancy.
In space, you are dealing with a lessening or an absence of gravity. Under water, bouyancy is counteracting it. The result is the same but the cause is not.
When you are in space, no matter which way you turn, blood will not go rushing to your head any more than when you are in any other position. If you turn upside down under water, you still feel the blood rushing to your head. Why? Because, even though you are relatively neutral in the water, the force of gravity is still there.
If you die underwater, I also suspect that blood will eventually pool in lower areas.
Another (gruesome) thought experiment:
You have a dead body hanging vertically in the air. You cut off the head and feet simultaneously. What happens?
Now you do the same thing to a body underwater. Does the same thing happen?
[I'm going to bed so here are the answers: for #1, the blood all pours very quickly out of the feet, because at the site of the cut, the pressure inside the blood vessel is much higher than the surrounding air, because of the weight of the column of 5 feet of blood. In #2, some blood will dissolve out through the neck and feet, and since blood is very slightly more dense than water, it may very slowly drain out of the feet if you leave it there long enough, but it does not pour out of anywhere. This is because the pressure in the blood vessel due to the height of the 5 foot column of blood is going to almost exactly equal the pressure in the water surrounding the site of the cut, because you have an equivalent amount of water there.
You have to think in terms of what would be FORCING the blood to move. In the case of air, the fact that the 6 foot column of blood - the body - WEIGHS so much more than the 6 foot column of air containing it means that your blood wants to SINK in that column of air. When in the water, the 6 foot column of blood WEIGHS almost exactly the same as the 6 foot column of water containing it, the blood has NO TENDENCY TO SINK.]
BTW, the "red water in a ziploc bag" is a perfect analogy. The human circulatory system is riddled with muscles, valves, and all sorts of other tissue, but the compelling physics involved are VERY well illustrated by the bag. In water, the blood has NO TENDENCY TO SINK because it's the same density as the surrounding water.
You have a dead body hanging vertically in the air. You cut off the head and feet simultaneously. What happens?
Now you do the same thing to a body underwater. Does the same thing happen?
[I'm going to bed so here are the answers: for #1, the blood all pours very quickly out of the feet, because at the site of the cut, the pressure inside the blood vessel is much higher than the surrounding air, because of the weight of the column of 5 feet of blood. In #2, some blood will dissolve out through the neck and feet, and since blood is very slightly more dense than water, it may very slowly drain out of the feet if you leave it there long enough, but it does not pour out of anywhere. This is because the pressure in the blood vessel due to the height of the 5 foot column of blood is going to almost exactly equal the pressure in the water surrounding the site of the cut, because you have an equivalent amount of water there.
You have to think in terms of what would be FORCING the blood to move. In the case of air, the fact that the 6 foot column of blood - the body - WEIGHS so much more than the 6 foot column of air containing it means that your blood wants to SINK in that column of air. When in the water, the 6 foot column of blood WEIGHS almost exactly the same as the 6 foot column of water containing it, the blood has NO TENDENCY TO SINK.]
BTW, the "red water in a ziploc bag" is a perfect analogy. The human circulatory system is riddled with muscles, valves, and all sorts of other tissue, but the compelling physics involved are VERY well illustrated by the bag. In water, the blood has NO TENDENCY TO SINK because it's the same density as the surrounding water.
jonnythan:
I think this is related to the similarities in the fluids an the slight difference in the S.G. of each. Eventually the blood will drain down.
If you are correct, hang up the corpse, put it in a pressurized vessel in air and lop off the top & bottom. Will the blood stay? No, the blood will run right out. It will not be slowed like it would immersed in water.
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