What is the effect on gravity underwater?

[WarmWaterDiver]

Bravo, Simbrooks. Appreciate the injection of physics / science back in here.

 

[No Fish]

The lower you go below sea level, the greater the force of gravity relative to being at sea level - and vice versa.

Don't disregard the mass of the water above you in the calculation.

 

[WarmWaterDiver]

Don't disregard the mass of the water above you in the calculation.

I think you'll find it's not statistically significant relative to the mass of the rest of the planet (remember there is a mantle & a core, and how relatively shallow the mohorovicic discontinuity lies in relation to the core). The deepest waters are a very thin skin - likes pores on an orange

Check the math . . . show your work (the numbers)

 

[Mick_O]

Don't disregard the mass of the water above you in the calculation.

I think that since you're not actually touching the hard surface of the planet while in the water column, you might as well be floating in thin air - I think the gravitational pull on your body would be close enough to identical whether you're in water, or at the same distance from the center of the earth, only somehow floating in air. Like simbrooks put it, except in graphical form:

It's hard showing mathematical formulae without LaTEX or one of them page description languages.
Basically - the mass of the water above you has to be included in the total of the earth's mass. Otherwise that mass would get smaller and smaller, the closer you get to the core - which it of course doesn't.

 

[WarmWaterDiver]

Mass and weight are not the same . . . and the core does not comprise the entire, nor bulk of, the mass of planet Earth.

Note that a lunar astronaut on the Moon's surface weighs less than the same astronaut weighed on the Earth's surface, yet retains the same mass - back to high school physics - but yet, the moon is smaller than the Earth - but while on the Moon's surface, the gravitational effect of the Earth is pretty much negiligible on the astronaut - that inverse proportionality to the square of the distance that was mentioned.

And that the mass of the Earth is pretty much independant of whether an object is on its surface, in its mantle, or at its core - unless you're getting into Einsteinien stuff where you're closely approaching the speed of light so your mass is a significant fraction of that of the Earth??? And if so, I think its your mass that would be significantly changing, not the Earth's. No physics class I ever attended demonstrated the mass of an inanimate object like a planet (or layer of water) being dependent on the location of an observer relative to the planet (or layer of water).

 

[No Fish]

I think you'll find it's not statistically significant relative to the mass of the rest of the planet (remember there is a mantle & a core, and how relatively shallow the mohorovicic discontinuity lies in relation to the core). The deepest waters are a very thin skin - likes pores on an orange

Check the math . . . show your work (the numbers)

Very funny, I was trying to make a point,,,, shall you mention depth, salinity, posotion of the moon,

And yes I can show my work, but you can't make me. I would also think that the average thickness and density of the craton or lithosphere, (if you are more comfortable with that), providing you are positioned appropriately, and any mitigating factors of nearby mass related to terrain, should be taken into account. Due that the Moho is somewhat plastic, and the core likely being ill defined and somewhat fluid, we should use averages... ......... Maybe we should just look it up.:06:

 

[simbrooks]

Has anyone even consulted any references on physiology here? I will check mine tonight... i found nothing in the US Navy publications on a quick skim through the pdf copy i have.

Well i checked my physiology book (Bookspan) and deco book (Weinke) and neither touches on the subject, i also googled a bit too, nothing there really either - so that leads me to several conclusions:
1) No one really cares about it
2) No one has done any conclusive test or come up with any results/suitable answers
3) We are arguing over something that for all intents and purposes is inconsequential and purely academic in nature
4) If its so important then someone needs to get out there and do some tests

Back to you regularly scheduled gravitational/planet/mass physics 101

 

[WarmWaterDiver]

Very funny, I was trying to make a point,,,, shall you mention depth, salinity, posotion of the moon,

And yes I can show my work, but you can't make me. I would also think that the average thickness and density of the craton or lithosphere, (if you are more comfortable with that), providing you are positioned appropriately, and any mitigating factors of nearby mass related to terrain, should be taken into account. Due that the Moho is somewhat plastic, and the core likely being ill defined and somewhat fluid, we should use averages... ......... Maybe we should just look it up.:06:

Once you look it up, why not post it - the real point of my discussion is such things are SO many orders of magnitude (powers of ten) LESS than the mass of the rest of the planet, even if one was at the interface between the crust and the rest of the planet, which is deeper than any body of water. This is the point I made. Knowing that, any other such masses still above the crust are only even further reductions in order of magnitude of effect. A simple screening that clearly demonstrates how negligible the water above one has on the effect of gravty on one while underwater vs. the effect of gravity on one at any other point between the surface of the earth and the crust of the earth - the difference (change, delta) is negligible. The good old double operator of << (much, much less) is what this is about.

Any claim to the contrary can be quickly resolved by doing the math, whether you choose to post the numbers or not.

Fluid Pressure can be manipulated while still in a gravity well - one can use pumps to make liquids flow uphill - but that doesn't change the effect of gravity on the fluid significantly - just pressure. Fluid presure can also be manipulated while outside a gravity well - the squeeze tubes of foods used by the astronauts for foods since the early days of the space program clearly demonstrate that.

 

[Rick Murchison]

An open bottle is not a human body.

No, it isn't. But it demonstrates the tendency of blood to flow "downhill" under water - which it doesn't, whether it be inside or outside your body. When you're topside the blood does try to flow downhill, and, absent the valves in and muscles around the veins, the blood would pool in the lowest parts of the body. (if we had an exoskeleton, instead of elastic skin, that would take care of it, but we don't, so it takes valves and muscles to keep your feet from blowing up like a balloon) Ask any vascular surgeon. (or ask me - I've had to have my veins stripped out of my left leg because I blew all the valves out pulling G's - submerging the leg relieves all the gravity pressure in the veins and allows an effortless return flow)
Perhaps a little factoid will help... it takes the same pressure to pump water (or blood) out the top of a vertical pipe eight feet long that has six of those feet above water as it does to pump water (or blood) out the top of a vertical pipe that is twenty feet long that has six of those feet above water. There'll be a tiny bit less flow in the longer pipe due to friction, but the pressure to get the water to the top of either pipe will be the same. This is true for the same reason that blood in the body doesn't seek "down" when submerged.
S

 

[No Fish]

Once you look it up, why not post it - the real point of my discussion is such things are SO many orders of magnitude (powers of ten) LESS than the mass of the rest of the planet, even if one was at the interface between the crust and the rest of the planet, which is deeper than any body of water. This is the point I made. Knowing that, any other such masses still above the crust are only even further reductions in order of magnitude of effect. A simple screening that clearly demonstrates how negligible the water above one has on the effect of gravty on one while underwater vs. the effect of gravity on one at any other point between the surface of the earth and the crust of the earth - the difference (change, delta) is negligible. The good old double operator of << (much, much less) is what this is about.

Any claim to the contrary can be quickly resolved by doing the math, whether you choose to post the numbers or not.

Fluid Pressure can be manipulated while still in a gravity well - one can use pumps to make liquids flow uphill - but that doesn't change the effect of gravity on the fluid significantly - just pressure. Fluid presure can also be manipulated while outside a gravity well - the squeeze tubes of foods used by the astronauts for foods since the early days of the space program clearly demonstrate that.

The point I was trying to make is the same one you are elaborating, that is why I said careful. Many folks do not have a strong grasp on physics, or geoligy for that matter, and they sometimes misunderstand or attribute 'more effort than it it is worth' to some incredibly minor concern. ie the hydronamics of tucking your suit inside or outside of your boots.

I was, afterall, being a bit facetious, one of my hobbies. You realize....I am on your side on this......