Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: Eric A. Taylor on 18/04/2010 19:15:37
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In the 50's or 60's there was a guy who volunteered to ride a rocket sled to test G force tolerance in humans. He experienced somewhere around 50 or 60 G's but suffered some injury to his eyes and bruising where the straps pressed into him.
A few years ago an F-18 pilot survived a crash in which he struck the ground with the plane in a nose high attitude (the crash can be seen on Youtube) and it's been calculated he experienced 75 Gs, though he suffered very bad injuries including breaking most of the bones in his face, both arms and both legs, and his his back. He is now 3 inches shorter than before the crash. This it is said to be the highest G load ever survived.
I know that duration has a lot to do with G tolerance. Can a person learn to work under higher G loads full time? I've personally experience 3 G's and found it possible, but very difficult to lift my arms (very strange feeling).
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I guess, guess okay:) that it's the same with that as with working under weightlessness. Our bodies processes works perfectly well under one G. Change that and your body will have to adapt, before functioning as we are used too. There have to be some leeway too it of course, but I would still expect this to be a rule going both ways.
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your G-tolerance highly depends on your own weight, 2G is twice your own weight, 3G is 3 times your weight.
if you weigh 100 pounds you'll weigh at 2G 200 pounds, 3G 300 pounds.
so there are 4 issues:
maximum weight you can handle, even WITH adapting. cause each G above 1G is another you on your back and getting more powerfull adds muscle adds again WEIGHT.
joint damage, 200 pounds can already stress your joints heavely.
law of Newton, the gravitational acceleration, if you drop your leg at 3G without force holding it up you'll get a speed of about 100 feet/sec it falls, with it's tripled weight. on earth it's 32 feet/sec it falls and you'll have a normal weighted leg.
so your leg can be easely oblitherated at even 3G when trying to walk like on earth. each feet you let go of something is equal to 3 feet on earth falling.
calories. these will eventually burn faster than you can consume since the labour will reach a point where it exceeds your energy consuming since we can't process fast enough at some point, and if you can, you'll just gain weight from the eating that burns even more calories.
anyone objects on my statements?
I think the maximum is around 1,2 to 1,5G to be able to live in for humans for longer periods of time.
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OK, lets start with the fact that the OP asked for a maximum G force that can be survived and pointed out that there are recorded cases of people surviving 75G.
That being so, any claim for less than 75G is plainly not a maximum and so it's not what the OP asked for.
Muscles can generally support more than their own weight so adding muscle adds more than enough strength to hold it up. Therefore, to a degree, adding muscle will always help.
The possible problem is that the skeleton won't stand the load, but that's another issue.
Most reasonably fit healthy men can carry their wives across the threshold of their new homes. (also most people can carry another using the "fireman's lift"). To do that they need to hold their weight plus the other person's weight. Roughly twice their weight. Also, to walk they have to carry roughly twice their weight on one leg. A long time ago when I was a teenager I did some weightlifting. I could easily lift over 250Kg using the muscles of my legs and back. That would have been about 4 times my weight. I wasn't one of the well muscled blokes in the class either.
It figures that, using both legs, they can hold four times their own weight.
In order to accelerate my leg to 33 f/sec under normal gravity I would have to let it fall for 1 second, but in 1 second it would fall a long way- (very) roughly 15 feet.
My legs are not that long.
The idea that I could get my legs to 100 f/s without jumping off a cliff is silly. You have not understood Newton's laws properly.
Even then reaching 100 f/s doesn't do any harm. Falling off a cliff probably never killed anyone. Hitting the ground did.
If you drop a rock off a table and it accelerates (at 1G) for 1 metre then it lands on the carpet and is brought to a halt in 1 cm (that's 1/100 Metres) the mean acceleration it experiences as it stops is 100 G.
I think I can manage 10 G falling down stairs.
There are people who regularly consume roughly 4 times the "normal" calorie intake. Lumberjacks and racing cyclists are the ones usually cited.
There's simply no evidence concerning what levels people could put up with for any length of time, but the unfortunate answer might be rather less than 1 G. Ask any of the large number of people with bad backs, arthritis etc.
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well he asked for long term tolerance so I answered. see the last two sentences.
muscle stays constant in strength if the G's go up, and it's true that it's possible that most people can lift 4x their weight with the legs but that doesn't mean they can do it at constant rates.
further more, you'll might get an endless need for muscle since you'll need more power in the beginning to adapt, but when you gained power you'll need more again because you gained weight due to muscle.
you'll die definitely in such case.
I do understand the law of Newton, I never stated that the leg falls a second, did I? [;)]
Newton G's on impact (force) isn't the same as graviton force on the body when falling. your comparing two completely different things with eachother.
(at 3G's) a triple weighted leg at triple the usually acceleration speed and a decreasing amount of milliseconds of deceleration time of the force on impact of the material definitely will give more of a problem than simply falling off some stairs.
100 G's is fine, but those factors apply too on how those are spent on the body and the more speed and weight the less it spreads the impact.
triple weight same speed = 3x amount of impact force/square cm • s‾¹, same weight triple speed is a bit more than 3x the impact force/square cm • s‾¹ since there is less deceleration time on the material (s‾¹). but triple weight and triple speed definitely isn't triple the impact force/square cm • s‾¹.
or am I thinking too complicated? [???]
I doubt you apply the laws of Newton correctly with your rock example, you probably mean a rock falling 1 second instead of 1 metre, right? [:)]
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One formula 1 driver (David Purley) suffered ~180g, but just barely survived. I think his car stopped in a few feet or something ridiculous. He was very, very lucky to make it. I think his heart stopped several times in hospital.
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I don't know what the largest g-force that can be survived long term, probably 2-3g.
Somebody tried it with chickens though: 'The great mambo chicken'. Google it....
Basically they raised chickens at high g-force (1.5g or 2g I forget). Then they stopped it and out walked ... Great Mambo Chicken.
Drumsticks to die for. I kid you not! Those muscles had been fighting gravity and growing all the time.
The evidence is that high-g increases lifespan if anything. Low g seems to do the opposite, but there's not been enough low-g to be sure (all experience is at 1g or 0g, but nothing inbetween- 0g is definitely BAD for you.)
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" if you drop your leg at 3G without force holding it up you'll get a speed of about 100 feet/sec"
That's not what Newton's laws would say, but it is what GBC89 says.
One of them needs to understand that g is about 32 feet per second per second (and it's not Sir Isaac).
"I doubt you apply the laws of Newton correctly with your rock example, you probably mean a rock falling 1 second instead of 1 metre, right? "
Nope.
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I said:
if you drop your leg at 3G without force holding it up you'll get a speed of about 100 feet/sec it falls
is also:
if you drop your leg at 3G without force holding it up you'll get a speed of about 100 feet PER second it falls
so I never stated it really falls a second, I just stated the acceleration in the appropriate SI-units.
got it now? [???]
and your right about that, it's 100 G.
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Ah, I see what you meant now, it wasn't clear but I presume English isn't you first language.
What you should have said was
if you drop your leg at 3G without force holding it up you'll get a gain of speed of about 100 feet/sec for each second it falls
The number 100 refers to an acceleration, not a speed.
However the bit that follows it doesn't make a lot of sense.
"so your leg can be easely oblitherated at even 3G when trying to walk like on earth."
A leg hitting the ground at 100 f/s might well get damaged, but there's no reason to imagine that just 3G would obliterate anything.
Incidentally, if you think the foot per second is an SI unit you still have some learning to do.
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well I presumed that without saying it falls actually a second no one would assume I actually meant a second, which I don't.
anyways, it's been a while since I needed physics.
but now I know how to apply it again, I think, so correct me if I'm wrong [;)]
calculation of your rock at 3G's
0,25 sec • 0,25 sec • 0,5 • 30 metre/second = 0,9375 metres. so my assumption is roughly taken 0,25 sec falling time before it hits the ground.
speed = 0,25 seconds • 30 metres per second = 7,5 metres/second.
avarage = 3,75 metres/second
0,01 metre / 3,75 metre/second = 0,00266666666 seconds decelleration time.
3 (3•1G, so weight replaced by G's) • the avarage speed / decelleration time = force in G's.
3 • 3,75 / 0,0026666667 = 4218 G
this'll be 4218 G with just 2 extra G's.
(roughly taken) 42 times more impact in this example, am I right or not?
EDIT: and I changed it into feet/second in my reply, I forgot that I did that when I placed my former reply...
I usually calculate in SI-units.
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As the rock falls gravity does work on it and it gains energy proportional to the distance it falls. (work = force times distance)
When it hits the carpet it transfers that energy to the carpet; that energy also is the product of the force and the distance travelled.
Since the distance is 100 times less the force must be 100 times more.
Since F=MA the acceleration must be 100 times more i.e 100G
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yeah that's right, but what about my calculation above of your rock at 3G?
did I do it right or did I made some error in it?
OK, lets start with the fact that the OP asked for a maximum G force that can be survived and pointed out that there are recorded cases of people surviving 75G.
That being so, any claim for less than 75G is plainly not a maximum and so it's not what the OP asked for.
last sentence of him, he said:
I know that duration has a lot to do with G tolerance. Can a person learn to work under higher G loads full time? I've personally experience 3 G's and found it possible, but very difficult to lift my arms (very strange feeling).
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your G-tolerance highly depends on your own weight, 2G is twice your own weight, 3G is 3 times your weight.
if you weigh 100 pounds you'll weigh at 2G 200 pounds, 3G 300 pounds.
so there are 4 issues:
maximum weight you can handle, even WITH adapting. cause each G above 1G is another you on your back and getting more powerfull adds muscle adds again WEIGHT.
joint damage, 200 pounds can already stress your joints heavely.
law of Newton, the gravitational acceleration, if you drop your leg at 3G without force holding it up you'll get a speed of about 100 feet/sec it falls, with it's tripled weight. on earth it's 32 feet/sec it falls and you'll have a normal weighted leg.
so your leg can be easely oblitherated at even 3G when trying to walk like on earth. each feet you let go of something is equal to 3 feet on earth falling.
calories. these will eventually burn faster than you can consume since the labour will reach a point where it exceeds your energy consuming since we can't process fast enough at some point, and if you can, you'll just gain weight from the eating that burns even more calories.
anyone objects on my statements?
I think the maximum is around 1,2 to 1,5G to be able to live in for humans for longer periods of time.
Sorry no idea what you're saying here. Doesn't make much scene. Acceleration (change in velocity not just speeding up) of 32 feet per second squared (32 f/s/s) is 1 G. What this means is if you accelerate at 1 G for 1 second you will be moving at 32 feet per second (about 22 miles per hour) 1G is considered "standard" as it is the force we experience on Earth. Of course concepts like "feet" "meters" and "seconds" are completely arbitrary. You can translate feet to meters, to miles, or kilometers, or even AU or light years. To an Alien "1 G" would have no meaning at all. Likely there home planet would have a different mass and size and thus a different gravity. And how do you accurately tell an alien how long a second takes, or how far you have to go to move 1 foot?
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yeah that's right, but what about my calculation above of your rock at 3G?
did I do it right or did I made some error in it?
OK, lets start with the fact that the OP asked for a maximum G force that can be survived and pointed out that there are recorded cases of people surviving 75G.
That being so, any claim for less than 75G is plainly not a maximum and so it's not what the OP asked for.
last sentence of him, he said:
I know that duration has a lot to do with G tolerance. Can a person learn to work under higher G loads full time? I've personally experience 3 G's and found it possible, but very difficult to lift my arms (very strange feeling).
OK, so he says he experienced a sustained 3G (rather than a shock loading like a plane crash) for long enough to say it felt odd and, in response to this you say that the biggest sustained acceleration you could survive is 1.5G
There's certainly an error or more in your calculation. It's hard to say where because it's not clear what you are doing.
If you were right about a couple more g of acceleration giving rise to 4200 g more deceleration then you would break the conservation of energy.
I think you need to look here.
http://en.wikipedia.org/wiki/Equations_of_motion
Find the equations you need, calculate the accelerations etc properly (preferably in SI units) and then see what you get.
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yeah that's right, but what about my calculation above of your rock at 3G?
did I do it right or did I made some error in it?
OK, lets start with the fact that the OP asked for a maximum G force that can be survived and pointed out that there are recorded cases of people surviving 75G.
That being so, any claim for less than 75G is plainly not a maximum and so it's not what the OP asked for.
last sentence of him, he said:
I know that duration has a lot to do with G tolerance. Can a person learn to work under higher G loads full time? I've personally experience 3 G's and found it possible, but very difficult to lift my arms (very strange feeling).
OK, so he says he experienced a sustained 3G (rather than a shock loading like a plane crash) for long enough to say it felt odd and, in response to this you say that the biggest sustained acceleration you could survive is 1.5G
There's certainly an error or more in your calculation. It's hard to say where because it's not clear what you are doing.
If you were right about a couple more g of acceleration giving rise to 4200 g more deceleration then you would break the conservation of energy.
I think you need to look here.
http://en.wikipedia.org/wiki/Equations_of_motion
Find the equations you need, calculate the accelerations etc properly (preferably in SI units) and then see what you get.
What I mean is that I experienced 3 Gs for a few seconds. Fighter pilots can pull more than 9 Gs and hold if for a few seconds. However this can only be done with a lot of training and some special equipment. And you have to be in VERY good shape to do it. You might find a fat ass bomber pilot from time to time but you will never find a fat fighter pilot!
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Interestingly female pilots in general tend to tolerate G-force better than male pilots.....Maybe because they keep more blood in the upper body?