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Sudden Impacts to the Head

by BazingaMan
Tags: force, velocity momentum
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Nov4-12, 06:25 PM
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Hello world. I am in the process of writing my first true college essay, a ten-page piece on some topic relevant to my University Physics I course, but I need a little help finding some information. Google hasn't been very helpful today, and I don't even want to think about combing our terribly organized library.

Anyway. What I would like is to know the typical human's tolerance to being hit in the center of the forehead - by a thrown rock, for example. What amount of force would the rock have to have in order to kill an individual, or at least cause severe trauma?

If I need to be more specific, then please let me know. All responses need to include some credible, cite-able source. Thank you.
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Simon Bridge
Nov4-12, 11:56 PM
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Welcome to PF;
Damage to the human body is generally a complicated subject so you have picked a great topic for an essay.
Is this a physics/engineering or a biology/medical essay?

Basically your head is a thin shock-absorber over a hard shell with a bunch of delicate tissue in liquid inside it. So there are several things that can be damaged. The biggest thing to worry about is bruising through the brain - eg. if the force of the blow throws the head back hard, the law of inertia has the brain hit the front and then the back of the skull-cavity. Once bruised, the brain can swell up. Since the skull of an adult won't flex, this swelling can be fatal.

You also need to worry about shock-waves through the head and, of course, possible fractures.
Nov5-12, 02:50 AM
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Quote Quote by Simon Bridge View Post
if the force of the blow throws the head back hard, the law of inertia has the brain hit the front and then the back of the skull-cavity. Once bruised, the brain can swell up.
Another fatal thing that happens during strong head acceleration: Blood vessels connecting brain and skull are torn apart, causing internal bleeding.

Nov5-12, 07:31 AM
P: 3
Sudden Impacts to the Head

The essay as a whole actually isn't about damage to the human body. I'm trying to explore the physics (or really, the violations of physics) behind The Flash. One of the topics I am trying to cover involves getting hit in the head; i.e., he can somehow run at superspeed and withstand the accompanying drag forces, but still has a normal human's capacity to withstand blows to the head.

As silly as this may sound, I'm looking for information similar to what they frequently talk about on Mythbusters: the number of "g's" a human head can withstand for a certain length of time before causing serious injury. It really doesn't matter what causes it, to me. If anything, throwing a rock may actually be the wrong approach; the numbers I crunched last night turned out to be puny.
Nov5-12, 04:38 PM
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A rock will give you other issues than acceleration of the head, I think.
In addition, rocks, punches and similar impacts are effective because they apply a strong force over a short timescale. Drag forces would be nearly constant if Flash runs in a straight line, and predictable even in curves. It is possible to balance another human (and even a small car) on a head, this corresponds to a force of ~800N parallel to the spine.
Simon Bridge
Nov5-12, 08:53 PM
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... though iirc the Flash accelerates to vision-blurring speed in well-under a second ... from a standing start. Working out what this means in terms of stresses on his body would be an interesting essay.

Though Flash's power could include some cushioning to the brain while he's accelerating that is not normally in force, i.e. when surprised. A bit like how a boxer can withstand strong blows to the stomach when braced.

There's a lot there though - i.e. I recall the TV show regularly had his shred his clothes running but his skin didn't even turn red. They also had him super-speed through doors so fast the motion wasn't visible (also didn't displace any air or damage the door).
Nov6-12, 08:34 AM
P: 3
Okay, I obviously need to be extremely clear in order to get my meaning across. I realize that the stresses that extreme accelerations would have on his body are severe, but I'm not concerned with that at the moment. I just want to know about blunt trauma to his head and brain. I have already granted him a miracle ability to withstand these accelerations without snapping his neck.
Nov7-12, 01:15 PM
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One of the things to worry about with head trauma is tearing the dura mater that surrounds your brain. It feels a bit like saran wrap that is filled with veins and CSF.

This review article mentions tested mechanical strength of dura mater and other nervous tissues:

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