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Offline AvengingAngel007

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free fall
« on: 10/10/2003 07:21:06 »
I have currently encountered a problem and I have come to seek your help. What is the largest distance a person can free fall and still survive? Also, how much physical force is the body capable of withstanding (Newtons)?
 
If you were wondering, I am doing a physics assignment on the chances of a person's survival during a free fall based on the criteria of height, velocity, and the amount of physical force a person can withstand.


 

Offline Ians Daddy

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Re: free fall
« Reply #1 on: 10/10/2003 15:32:27 »
I think it would probably differ greatly. I may be wrong and there could be a formula, but I'm guessing that it would differ. Some freak accidents have proven that sky divers have survived parachute failure. Some people fall off the couch and die. I don't know if it's a physical thing or a mental thing. I'm guessing it would be like figuring if a skinny guy or a fat guy would die first from a gunshot wound. My perception is that "fight or flight" is a big factor. Now, I know it takes a certain amount of pressure to break certain bones and I'm sure organs apply as well. God probably has something to do with it too. But, that's just my opinion. I like to put my 2 cents in. Hope you get a more concrete answer.
 

Offline tweener

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Re: free fall
« Reply #2 on: 10/10/2003 19:58:45 »
I have to agree with Ians Daddy.  It really depends on a lot of factors.  However, as an academic exercise, that is probably not a good answer.  I don't know where to find the tables, but I'm sure that NASA and the military have extensive data on the forces the human body can withstand.

No words of wisdom here.
 

Offline Donnah

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Re: free fall
« Reply #3 on: 11/10/2003 01:47:15 »
Assuming there were no limitations on how high you could begin, you would either have to wear an air tank and mask, or I should think that eventually the speed would make it impossible to breathe[:0].
« Last Edit: 11/10/2003 01:47:58 by Donnah »
 

Offline bezoar

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Re: free fall
« Reply #4 on: 11/10/2003 03:38:30 »
Didn't we have this discussion once before -- something similar about people jumping off of high buildings?  I've read the same stories about jumpers whose parachutes didn't open.  And one story was about a guy who parachuted out in a thunderstorm, whose chute did ipen and he was kept aloft for several hours by the wind gusts.  I wonder if you could reach a speed that would make it impossible to breathe -- or maybe your adrenalin would.
 

Offline UScaV

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Re: free fall
« Reply #5 on: 14/10/2003 06:03:26 »
I suppose if you were being blown by the wind(like an uber super godly wind from hell kind of deal) it could be possible to go so fast you couldn't breathe.  But when you're free falling, the body reaches a terminal velocity, I think for an average person it's something like 120 mph.
 

Offline chris

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Re: free fall
« Reply #6 on: 16/10/2003 00:23:19 »
I thought terminal velocity was closer to 120 mph, but I might be wrong.

About the impact of the atmosphere there is a guy (French I think) who is training to free fall from space. He estimates that he will be doing about 20 miles a second at his fastest.

Apparently the biggest problem is preventing yourself from going into a spin since at 20 miles a second it's likely to be quite a fast spin and certainly sufficient to liquidise your brain.

Others have tried the same feat. One guy landed. Though dead on arrival he was accused nonetheles of cheating because he used a small chute to control the attitude of his freefall - unfortunately it didn't work too well and he went into a terminal spin.

Chris

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Offline NakedScientist

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Re: free fall
« Reply #7 on: 16/10/2003 00:29:36 »
We have indeed talked about this subject before. A quick search (using the extrmely good search facility above !) found an item called "just a randsom thought" posted by Rach217. Exodus contributed the following to the debate which confirms Chris's suspicions that terminal velocity is about 120 mph :

"...As for your view on impacts... yes its an impact, but the height of a garden shed would not give your body enough time to accelerate to terminal velocity. This is the maximum speed you reach within freefall. For example, a skydiver is known to have a terminal velocity (with chute closed) of about 200 km/h, which is around 124 miles an hour (54m/s).

Also:
The more compact and dense the object, the higher its terminal velocity will be. Typical examples are the following: raindrop, 25 ft/s, human being, 250 ft/s.

(Bueche, Fredrick. Principles of Physics. New York: McGraw Hill, 1977: 64.)

Thus if you jump froma high building then when you impact, you will be close to the terminal velocity. This wouldn't be the case from jumping from a shed, hence you wouldn't die unless there was a rusty fork or rake on the floor or something..."
 

Offline UScaV

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Re: free fall
« Reply #8 on: 17/10/2003 03:52:56 »
Assuming you never reached Terminal velocity somehow with an atmosphere that had air in it, how fast would you have to be going to not be able to breathe (assuming you wouldn't tear apart either)?
 

Offline chris

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Re: free fall
« Reply #9 on: 17/10/2003 13:31:25 »
You breathe in because atmospheric pressure forces air into your lungs because the expansion of the chest reduces the pressure inside youor chest compared with the outside world and air enters. Your ribs move outwards as well as towards your face so you'd have to be going prety damn fast before the air was quite literally knocked out of you and you couldn't breathe out or in.

I'll look into it - an interesting question though.

Chris

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Offline Donnah

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Re: free fall
« Reply #10 on: 18/10/2003 01:18:16 »
What happens when a person gets the wind knocked out of her and she can't breathe?
 

Offline chris

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Re: free fall
« Reply #11 on: 18/10/2003 10:50:45 »
Why do people get winded following a fall or blow to the chest ? Good question.

I suspect that the impact of a blow to the chest or a fall onto the chest, (or a rugby scrum falling onto someone's chest), exhaggerates the elastic recoil of the chest wall which is is what pushes air out of your lungs when you breathe out.

More air leaving the lungs than normal would mean that the alveoli, or air sacs, are smaller than they should be, making them more likely to collapse. They probably re-inflate rapidly with the next breath but the irritation that this causes probably causes the winded individual to develop the spasm of coughing that goes on for a few minutes afterwards .

Indeed, in patients I've treated in hospital for a pneumothorax (air outside the lung causing lung collapse), as the lung re-inflates (when treated) they tend to cough a lot for a few minutes. This is down to a nerve reflex that signals the brain when the airways are irritated and also tells the brain how 'open' the airways are.

So, to conclude, I can't say for certain, but my guess is that when you are winded the ensuing shortness of breath and subsequent coughing to get your breath back occurs because a few alveoli were temporarily emptied of air and collapsed, then re-inflated !

Chris

"I never forget a face, but in your case I'll make an exception"
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« Last Edit: 18/10/2003 10:57:18 by chris »
 

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Re: free fall
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