How many Newtons of force would kill a person?

  • Thread starter Simfish
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  • #26
Why would we use a Black Hole for artificial gravity? The ship would not be able to escape the gravitational pull from the Black Hole and eventually get pulled past the Event Horizon.
Just using it as an example. Just picture whatever science fiction space travel device you want. Warp (bubble) drive, that black hole one (if people one day can make a black hole maybe they can shut it off) etc.
 
  • #27
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Just using it as an example. Just picture whatever science fiction space travel device you want. Warp (bubble) drive, that black hole one (if people one day can make a black hole maybe they can shut it off) etc.
Well if one day we could create, destroy and manipulate a Black Hole, I'm pretty sure we could forge something a little less destructive to harnesses gravity for us.
 
  • #28
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Is this for construction of free standing buildings? I didn't think QuantumPion's statement was confusing at all, RDave.
 
  • #29
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It's far too complicated a subject to even begin to estimate a single force, because as you said it depends hugely on where the force is exerted and over what area. But let's look at two situations, a penetrative situation and a blunt impact.

Penetration (or indentation) is hugely dependent on contact area. So the force required to cause penetration or indentation to the same depth will be lower for a sharp knife than a blunt knife. Hence why it requires a lot less effort to cut a tomato with a knife once you've sharpened it. Essentially, the knife needs to create a stress at the interaction with the incident sample that is greater than the cutting strength of the material, which is related to at least compressive strength and fracture toughness.

Blunt trauma injuries can range from the fracture of bones to internal bleeding to brain damage and even stopping the heart. For many of these injuries there are different theories as to causal criteria. Essentially, for brusing and contusion it's a function of applied stress to soft tissues, and for head injuries acceleration (both linear and rotational) are important.

When it comes to impacts, the force that is experienced by your body is determined by a variety of things. The speed of the falling object at impact (relating to rate dependency of the surface being hit), the mass of the falling object (determining the kinetic energy of the object at impact e.g. a 10kg mass falling from 1m has 10 times the kinetic energy of a 1kg mass falling from 1m), and most importantly of all the deformation characteristics of the surface being hit, because in the case of an impact, the peak force experienced by your body is related to how the object is slowed down to rest. After that, you have to consider the area over which it's acting again in a similar way to the penetration example.

Not meaning to ressurect a dead post, but I was hoping someone could help me figure out what to name this type of pysics.

I'm going to be working on a safety application as a hobby project, so I was trying to find some concrete material about this type "physics of human safety." I have a pretty good grasp on newtonian physics, so I understood everything in this post, but I was wondering if this type of stuff is written up in a book somewhere.

Most of the books I found on this type of topics seem to be "no calculus involved" for medical students type books. Does anyone have some suggestions?
 
  • #30
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How many Newtons of force would it take to have, say, a 50% chance of killing a person? How many would it take to hurt a person?
It isn't the force that would kill a person, but the stress. A person can undergo any size force and not notice it. What may kill a person is the stress and shear that the persons body is under. So the answer to your question is that force can't kill a person! However, the real question is what aspect of force would kill a person.
If the force were uniformly distributed, then every atom in the person would have the same force and the same acceleration. Therefore, the force wouldn't be noticed. It is inhomogeneities in the force that kills a person.
It is the gradient of force that would kill a person. The force has to be different in different parts of the body. If the force were sufficiently different on opposite sides of the body, or even on opposite sides of a vital organ, the person would die.
The gradient of force is referred to as the stress. A stress causes a strain. Strain is the gradient of displacement of the different parts of the body. If the strain is large enough, different parts of the body will move apart of move together. This would kill a person.
There are basically two types of stress: compressive and shear. There are maximum limits to each for various materials. Basically, what kills people in a fall is usually the shear stress. For example, a bone could break if enough shear is applied to it.
This is actually a problem in continuum mechanics. One has to know the maximum stress and shear of the bodies materials. Then, one has to determine what the actual stress and shear is under those conditions. This could be complicated in a system as complicated as the human body. No wonder scientists use accident dummies instead of computer simulations!
 
  • #31
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Based on typical ballistics numbers, 100 J seems to be the minimum lethal kinetic energy. This is roughly equivalent to a .22 long bullet (40 grains) from a rifle at 1000 fps. The next level of damage is at about 1000 J, which corresponds to a .357 jacketed soft-point (158 grains) bullet at 1400 fps. This is fairly lethal (depending exactly where it hit) to unprotected personnel. Lastly, something around 4000 J is sufficient to penetrate body armor. This is something like a 7.62 full metal jacket or .30-06 armor piercing bullet (166 grains) at 2750 fps. Roughly dividing this into three broad categories:

Light (.22 cal): 100 J.
Moderate (.357 cal.): 1000 J.
Heavy(.30-06 cal): 4000 J.
http://www.fas.org/man/dod-101/navy/docs/es310/dam_crit/dam_crit.htm

It appears that 1000J is required to get a Psubk of .5.

Daggs
 
  • #32
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At 3 secs, Force exerted is 154 N.(Assume sustained before then), then at 3.02 secs, force reaches 501262.875 N. At 3.05 secs, force has decreased to 47162 N and decreases until at 4.1 secs force is 712 N and stabilizes. Assume body is 100 lbs.
 
  • #33
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Is there a possibility that a large enough object could strike this planet at 1000+/- mph and stop us?
It would be a good exercise to try calculating how large a mass would be needed to produce that effect - conservation of momentum is all you need. Before you try it, be careful to define what you mean by "stop" and "moving at 1000 mph", as both have to relative to something - the sun might be a good choice.
 
  • #34
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Old thread rises from the dead.
 
  • #35
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At 3 secs, Force exerted is 154 N.(Assume sustained before then), then at 3.02 secs, force reaches 501262.875 N. At 3.05 secs, force has decreased to 47162 N and decreases until at 4.1 secs force is 712 N and stabilizes. Assume body is 100 lbs.
You have replied to a 2 year dead thread and I don't see a question in there. Is there something you need help with?
 

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