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View Full Version : another newbie type question thats sort of astronomy like

2003-May-28, 05:28 PM
This is something that has been in the back of my mind eversince seeing the movie "Event Horizon", very cool movie, could have been better, but i love sci-fi movies, therefore it was cool :D .

In the movie they used "Gravity Couch's" to prevent damage to the body during high G acceleration, it was basicly a big tank of water (or at least some sort of fluid) one of the actors lines were something like 'if you arent in a grave couch then when the engines fire, the g force will liquify your skeleton' :o not a pretty picture in my mind.

ive tried to figure out how one might work for real but dont really know if it makes sense, and i spent some time on the net trying to find out if there was any info on how such a thing might work (didnt want to post this if I knew someone else already thought of it) and couldnt find anything, so here goes....

In the tank you would effectively be weightless, with the water supporting you, but as the ship began to accelerate, wouldnt the water 'above' you begin to get heavier? and at very high acceleration wouldnt the effect be the same as if you were to go deeper and deeper under water, and therefor wouldnt the pressure inside the tank increase and crush you?

this was the problem i tried to figure out (assuming this would even happen), if the pressure increases as acceleration does, then how about starting in a pressurised tank (having undergone proper compression procedure and be breathing the proper exotic air mix), and -decreasing- the presure in the tank at the same rate as it increases (due to G forces) therefore making the pressure in the tank remain constant and keeping the person/chimp/bunny/whatever comfortable. Assuming you stayed boyant (excuse the spelling i think), that is to say you remained off the surface that the G forces were pushing you towards, the water would keep supporting you and you would stay cushioned to the G forces, then when the ship was up to speed (assuming it doesnt keep acceleration for half the trip), you could decompress and voila, siting in a nice, comfy very cool looking space ship going really fast.

I really dont know if this makes sense, and it could be a load of ******** there seems to be a lot of people in here who are a hell of a lot smarter than me (im not that smart), so by all means disect, rip it up and tell me if it could work (or if its ******** and im an idiot :) )

JackC
2003-May-28, 05:59 PM
Hi Invader Spleen (ugh!)

I am not a physicist or anything, but I think your initial analysis is right on - gravity is basically indistinguishable from inertia so those "Gravity Couches" really wouldn't do much, I don't think. 'Specially not with acceleration that would "Liquify your skeleton".

But I don't think your "solution" is worth much either! It isn't pressure but acceleration/inertia you are working with, which creates a pressure effect. You are increasing mass, really (incorrect wording - not "increasing" just increasing the inertial effect on...) not just pressure.

So - if you are in a tank of water, the inertial effect of acceleration affects EVERYTHING equally (assuming linear acceleration). Think of this - when you are floating at the TOP of a tank of water (or some other solution) and undergo acceleration, you would not sink (I don't think...) because ALL of the tank would be undergoing the same acceleration.

The reason high acceleration is damaging is that basically, your bits all want to stay in the same place. Acceleration needs to proceed in such a manner as to prevent the bits of you from staying in the same place long enough that other bits firmly attached to things like chairs don't simply push through the floaty bits. That would be bad.

The only really good SF way to counteract that effect would be to provide some form of "counter acceleration" on your specific bits that prevented them from being hurled "backward" (counter-accelration) through your spine. One presumes this is what things like Star Trek employ to keep people from becoming small stains on the wall.

Just my thoughts on the subject.

Oh - one other thing - acceleration of that magnitude is rather astonishing. I haven't done the math, but the force required to move what is presumably a very large ship at that kind of acceleration - well - I think it would also turn diamond into water. Or at least, something besides diamond. wonder what (fictional) material the SHIP is made of?

Jack

russ_watters
2003-May-28, 06:33 PM
To be concise - its not the support for your weight that is the problem, its the weight of your body itself. If your blood gets too heavy, your heart can't pump it. If your chest gets too heavy, your diaphram can't fill it with air. If your colon gets heavy, your sphincter can't - well, you know.

Eric Carlson
2003-May-28, 06:56 PM
I haven't seen the movie, but in principle, something like this should work, or at least help.

Suppose we approximate your body as being made of various parts (call them "organs") which must be in approximately the right place if you are going to be alive. If we assume that all these organs have a common density, then you can show that if we put you in a tank which is filled with liquid of the same density (call it "water"), then gravitational forces/acceleration are irrelevant to you.

The easiest way I have to understand this is to think in terms of energy. Gravity wants everything to be at the lowes tpossible position, hence if you go unconscious,you fall down. However, when you fall over, the air that is beneath you gets pushed out of the way, and therefore gets pushed up. But you are denser than air, so gravity/energy would rather have you down and the air up than vice versa. On the other hand, if you are floating in water, you don't go up or down much, because you are about the same density.

When you crank up the gravity, nothing really changes.

There are some problems, however. We are NOT actually uniform density. In particular, the air in our lungs has much lower density. If we are positioned upright, this means the pressure around our lungs makes it hard to breathe in. Indeed, I notice this when I'm swimming. My lungs have to work extra hard, even if I'm just floating/relaxing in a vertical position. I suppose lying prone and having air forced in with a pressurized system would help, but it gets complicated.

Our skeleton is also denser than water (I think). At sufficiently high gravity, this would cause our skeleton to sink to the bottom of our body while the rest floats on top, which sounds uncomfortable.

tracer
2003-May-28, 07:23 PM
Perhaps they were using that liquid breathing solution from The Abyss when they were in those acceleration tanks. They wouldn't have to worry about the air in their lungs getting compressed by their own weight, if their lungs were filled with liquid.

daver
2003-May-28, 08:04 PM
Someone could probably dredge up some references.

My guess is that immersion or semi-immersion in a liquid would help to maybe a dozen g's. Filling your lungs and sinuses with a breathable liquid roughly the same density as your body might double or triple that. Eventually, though, the differences in density of the parts of your body is going to start making itself felt, and you'll squish anyway.

newt
2003-May-30, 01:19 AM
Like Daver said, it's the relative accelerations of the different bits of your torso that will defeat you in the end. G-suits and re-orienting the body position (a la F-16 fighter pilots) may delay the onset of effects such as blood loss from the brain and percolation of blood oxygen, but pancake that jet plane into the runway and you're pink mush. The implication is that we will have to find some way of pressurizing or otherwise stiffening the human carcass (and its' fragile cell structure) from inside to resist elevated G's. Not even a rigid space suit (external protection) or cushioning medium would protect the body from itself in the extreme accelerations you allude to. Happy thoughts. Cheers.