15 lbs per sq inch. The Mendoza line of armed self defense?

15 lbs per sq inch.  The Mendoza line of armed self defense?

15 pounds per square inch.  That is the force required to crack open the human skull.  Doesn’t sound like much does it?  That’s because it isn’t.  But is it enough of a reason to defend yourself with a gun?  Does it cross the Mendoza line?

That is the question now being argued in the George Zimmerman case since the prosecution’s main witnesses basically blew up in his face.  The first, Rachel Jeantel, alluded that Martin was spoiling for a fight since he noticed a “creepy ass cracker” was following him.  The second, John Good, described the scene he witnessed with Trayvon Martin atop Zimmerman raining blows down upon him, “ground and pound style”.

So we find ourselves with a neighborhood watch captain, investigating a stranger in the neighborhood and then calling the police to report it, on his back being bludgeoned by a  middleweight.

This is the moment.  This is when the anti gun media and all the gun grabbers are going to point to and say that Zimmerman should have just gotten his ass kicked and the need to shoot was excessive.  It’s also the only play the prosecution seems to have been left by the debacle they orchestrated by their own witnesses.

15 lbs of pressure per square inch.  That is the threshold between living and probably dying.  That is when your skull with crack and shatter.  We all ready know that Martin was at least half way there because the amount of psi required to break a nose is between 7 and 9 psi.

Now, you may think that boxers get punched harder than this all the time.  You’re right, they do.  But the force of the punches that boxers  take(and anybody really) is dissipated by the body absorbing it and recoiling backwards.

BUT, when you are on the ground and your head does not have any room to recoil and dissipate the force, the threshold for damage is lowered dramatically.

To illustrate it in another way, think of a catcher in baseball being run into at home plate.

Now imagine that that catcher is against a wall.

That is the difference between a normal punch to the head and what George Zimmerman was facing that night.  What sane person can really try to justify that Zimmerman should have just laid there and took it and hope that Martin stopped before any permanent damage was done?

Oh yeah…these people:


Then again, I did say sane.

There are reasons that MMA refs stop fights quickly when a ground and pound is being done on an opponent without the ability to defend themselves.  And they aren’t fighting in the street getting their head smashed into the asphalt.

There wasn’t a ref to step in and help George Zimmerman that night.  So he defended his own life in the only way left to him short of just hoping that Trayvon Martin would stop killing him.



4 responses »

    • Not exactly. Considering we have evolved and adapted to our environment over the past millenia, the 15 psi necessary to fracture our skull is on top of the atmospheric pressure of Earth. If you were, let’s say, the clouds of Jupiter, where the atmospheric pressure is ten times as great the force needed to crack your skull (assuming it needed a catalyst and didn’t just implode on its own) would be little more than a flick of the finger.

      • Actually you don’t quite understand the physics involved. At ~10 m under water the pressure is about 2 atmospheres or close to 30 psi. Scuba divers heads don’t explode at 33 ft under water. Even if they bump their heads. Same is true at the usual limit for recreational scuba diving, ~130 ft with nearly 5x atmospheric pressure.

        Look at it this way, you can take a pencil eraser with a 1/4″ diameter which will have a surface area is ~0.05 sq. in. to get 15 psi you only need to press with 0.75 lbs, or the weight of 1.5 cups of water. Sorry but you wont crack your skull if you balance 1.5 cups of water on a pencil eraser on your head (you may get wet though).

        The misunderstanding seem to be based on confusing terms. PRESSURE is Force per unit area.
        What you want to be thinking about is IMPULSE per unit area. Impulse is defined as Force times delta(t).

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