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Author Topic: The final bullet that killed Kennedy -- and violent head wounds in general
RoofingGuy
The First USA Noel


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Ok, this has bothered me for a long time...

Pretty much everyone over 25 has seen Abraham Zapruder's film of the assassination (and probably quite a few under 25, but the film and the stills aren't shown as much anymore). We see the final impact, and we see a jet of cranial matter burst forward and Kennedy's head jerk back. Why, oh why does every author and researcher (and person-on-the street, for that matter) immediately say that the head moving backwards proves that the bullet came from the front?

It is a simple matter of physics.

First off, bodies in don't fly back ten feet through a plate glass window when someone gets shot, no matter what Hollywood thinks looks "cool". There is little to no motion of the target when a bullet strikes -- science says so, but even if you don't believe the math, Mythbusters did a nice episode about it. They hung a dead pig from a hook, such that anything more than the slighest motion would knock the pig off. Pistol? - hardly moved... high-powered rifle and shotgun? - maybe moved an inch... automatic rifle at full auto? - finally fell off the hook.

It's all conservation of momentum... you take a small projectile moving at high speed, and collide it with a stationary, much larger target, and the target's momentum hardly changes... and even less so if the projectile exits and keeps on travelling.

It was the violent jet of cranial matter shooting forward that caused the head to jerk back. Same concept as rocket propulsion -- you shoot hot gas out backwards, you move forwards, so that the total momentum of the exhaust/rocket system is conserved.

All the head moving back "proves", is that the jet shot forward... but we already knew this from the film and from where the jet contents landed. The actual shot could have come from anywhere, seeing as how the skull does have a nasty habit of bursting when dealt a blow, even when the blow doesn't penetrate (but a penetrating shot from the rear being the most statistically probable in this case).

If you don't like my physics, Luis Alvarez can back me up. The Nobel-winning physicist published the exact same conclusions in a 1976 physics journal that I recently found reference to.

Does this prove the bullet came from the 6th floor window? No. Does it prove there wasn't a second (or third or fourth) shooter? No. Does it even preclude multiple simultaneous impacts? No. But stop saying the motion of the head "proves" he was shot from the front. Dig through the archives and all the newly-released files and question the autopsy and the chain of evidence and everything else, if you like, but don't invent proof or ignore the truth -- that's what you're accusing the FBI and the Warren Commission of doing.

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Michael Cole
Deck the Malls


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INSULTINGLY STUPID MOVIE PHYSICS

Always worth a read...

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CaptainWunderpants
I Saw Three Shipments


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I first watched the Zapruder film in 94 and have intermittently asked myself the same question ever since, based on (thought provoking but completely irrelevant) observations when shooting roos.
Essentially I agree with you - except I'm not convinced about

quote:
Originally posted by RoofingGuy:

It was the violent jet of cranial matter shooting forward that caused the head to jerk back. Same concept as rocket propulsion -- you shoot hot gas out backwards, you move forwards, so that the total momentum of the exhaust/rocket system is conserved.


I would have thought that the violent jet of cranial matter shooting forward would suffer from the same lack of momentum (having a blank on the technical term - mass x velocity is what I mean) as a bullet, having a similar small effect on the inertia of the head as the bullet.

This is a guess done without calculations - I'm willing to learn that I'm wrong. To that end I'd love to read that paper if you have a cite.

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RoofingGuy
The First USA Noel


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quote:
Originally posted by CaptainWunderpants:
To that end I'd love to read that paper if you have a cite.

Well, the image quality is very poor at times, and most of Alvarez' article is talking about the timing of the shots and the acceleration of the car; the section on the motion of the head and the "jet" is fairly small. But I found the article here. I'll Google around and see if anyone has a clearer copy of that HSCA Appendix or the article itself.

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I refuse to get into a battle of wits with an unarmed person...

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Michael Cole
Deck the Malls


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quote:
Originally posted by CaptainWunderpants:

quote:
Originally posted by RoofingGuy:

It was the violent jet of cranial matter shooting forward that caused the head to jerk back. Same concept as rocket propulsion -- you shoot hot gas out backwards, you move forwards, so that the total momentum of the exhaust/rocket system is conserved.


I would have thought that the violent jet of cranial matter shooting forward would suffer from the same lack of momentum (having a blank on the technical term - mass x velocity is what I mean) as a bullet, having a similar small effect on the inertia of the head as the bullet.

This is a guess done without calculations - I'm willing to learn that I'm wrong. To that end I'd love to read that paper if you have a cite.

From memory, the head jerk was considered as being caused by a muscle spasm in the neck, and actually occurred slightly after the bullet hit.

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RoofingGuy
The First USA Noel


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quote:
Originally posted by Michael Cole:
From memory, the head jerk was considered as being caused by a muscle spasm in the neck, and actually occurred slightly after the bullet hit.

Well, even if the head jerk was muscular, and the "jet" wasn't strong enough to throw the head back, there still seems to be a small initial forward motion imparted by the impact Z312-Z313 which isn't inconsistent with a bullet strike from the rear, but would seem to be inconsistent with a frontal strike.

It still seems Zapruder in no way "proves" a shot from the front.

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I refuse to get into a battle of wits with an unarmed person...

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Pseudo_Croat
Angels Wii Have Heard on High


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"Back and to the left...."

- Pseudo "paging Oliver Stone" Croat

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The Rubber Chicken
The First USA Noel


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Penn & Teller do a demonstration of the concept on Season 3 of Bullsh!t. They take a honeydew melon and wrap it in seran wrap or something like that, put it on a pedestal, and shoot it with the same type of rifle that Lee Harvey Oswald used. The melon does indeed fall back towards the direction of the shot, while the melon innards fly forward with the bullet. If I remember correctly, they say their demonstration is actually a recreation of a demonstration done by the Warren Commission when investigating the assassination.

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robbiev - singin' off key
Happy Xmas (Warranty Is Over)


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quote:
Originally posted by RoofingGuy:

First off, bodies in don't fly back ten feet through a plate glass window when someone gets shot, no matter what Hollywood thinks looks "cool".

[slight hijack]

RoofingGuy,

You're my new best friend!

I'm a shooting instructor and you'd (generic you) be surprised how many people refuse to believe this, even after showing them videos that prove it.

More than once, someone has said to me that it MUST be true because that's the way they show it in movies. [Mad]
[\slight hijack]


on a side note: are you saying something's happened to president Kennedy? (25 pts for reference)

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Unusual Elfin Lights
Happy Xmas (Warranty Is Over)


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In my career I've had the opportunity to do a lot of ballistic work. Wound ballistics is my weakest area, but a quick google on the words Wound Ballistics turns up this gem of an article.

It is a wound ballistics article discussing Kennedy's fatal shot.

It is a bit technical but, from my limited experience, sound.

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Delta-V
Xboxing Day


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I've seen the film, and the stills, and the computer simulation of it all. It's obvious to me that at the point when the final shot hits Kennedy, his head is nearly in Jackie's lap, and he is leaning over. Any shot from the front above the level of the car's body would have gone straight into the top of his head. But the shot is pretty much inline with the direction Kennedy's head is facing. The only two possible angles that the shot could have come from are 1) from above, behind, and to the right of the car, or 2) a previously unknown assailant crouched on the floorboard in front of Jackie's seat.

It's also obvious, if you look at the layout of the seats (the car is in the Henry Ford Museum), that the middle row seats are positioned several inches inboard. Unlike the positions shown in JKF, Connelly wasn't directly in front of JFK, but farther towards the middle of the car, and turned so his body was nearly at the centerline of the car...directly in the path of a bullet through JFK from Oswald's position.

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All-American
Deck the Malls


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quote:
Originally posted by RoofingGuy:

First off, bodies in don't fly back ten feet through a plate glass window when someone gets shot, no matter what Hollywood thinks looks "cool".

The force being exerted backward on the person holding the rifle is equal and opposite to the force propelling the bullet forward. Since the person holding the rifle doesn't go flying backward, the person being impacted by the bullet won't go flying forward either. So, as you say, the plate glass window stays intact.

BUT, hold the butt of a high-powered rifle up against your face (okay, don't really or you'll hurt yourself) and fire the rifle. Will the rifle recoil jerk your head back? Probably yes.


quote:
There is little to no motion of the target when a bullet strikes -- science says so, but even if you don't believe the math, Mythbusters did a nice episode about it. They hung a dead pig from a hook, such that anything more than the slighest motion would knock the pig off. Pistol? - hardly moved... high-powered rifle and shotgun? - maybe moved an inch... automatic rifle at full auto? - finally fell off the hook.
Once again, the problem is that the mass of a pig is much greater than the mass of a human head, which weighs less than ten pounds.

quote:
It's all conservation of momentum... you take a small projectile moving at high speed, and collide it with a stationary, much larger target, and the target's momentum hardly changes... and even less so if the projectile exits and keeps on travelling.

It was the violent jet of cranial matter shooting forward that caused the head to jerk back. Same concept as rocket propulsion -- you shoot hot gas out backwards, you move forwards, so that the total momentum of the exhaust/rocket system is conserved.

This is where you go astray. You just claimed the momentum of a rifle bullet is not sufficient to move the head in the direction of the bullet, but it is sufficient to move the head in the opposite direction. This violates the conservation of momentum.

If the original momentum of the bullet is too small to move the head, the total momentum of the exiting bullet, skull fragments, and jet of cranial matter must also be too small to move the head. Unless you can show me where momentum (or energy) is being added to the system.

When Luis Alvarez asserts that the "jet effect" is enough to move Kennedy's head in the direction opposite to the bullet's trajectory, he's implicitly stating that the bullet's momentum is also enough to move the head in the same direction as the bullet. But he carefully neglects to mention this in his article.

Furthermore, his jet effect calculations contain serious errors which invalidate his entire assertion. He assumed the bullet exited Kennedy's skull intact, whereas in reality it fragmented into hundreds of pieces inside the skull. Hence, the total energy leaving Kennedy's skull was considerably less than he calculated. Also, he ignored the force exerted on the skull as the bullet entered it. If we're to believe the Warren Commission, the entire copper jacket on the bullet was peeled back from its lead core upon impact with the skull, which would've transferred a great deal of momentum to the head in the same direction as the bullet, and left even less momentum for the "jet effect".

Incidentally, more than one ballistics expert has questioned whether a copper-jacketed bullet (the ammunition fired from Oswald's Mannlicher-Carcano) would ever separate from its core in the manner supposed by the Commission. But that's a discussion for another time.

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All-American
Deck the Malls


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quote:
Originally posted by CaptainWunderpants:

I would have thought that the violent jet of cranial matter shooting forward would suffer from the same lack of momentum (having a blank on the technical term - mass x velocity is what I mean) as a bullet, having a similar small effect on the inertia of the head as the bullet.

Bingo! Either the bullet can move the head, or it can't. Regardless of direction.
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RoofingGuy
The First USA Noel


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Ok, again I left a key word out... I had meant to type that the loss of momentum of the bullet wouldn't drastically change the momentumum of the head, despite my actual saying it wouldn't change it at all (and as I posted later, the head does seem to move slightly forward just before the "jet").

quote:
Originally posted by All-American:
BUT, hold the butt of a high-powered rifle up against your face (okay, don't really or you'll hurt yourself) and fire the rifle. Will the rifle recoil jerk your head back? Probably yes.

And wouldn't that merely be how far a head would move in an inelastic collision where the bullet attaches to the head, stops and doesn't pass through? Where all the bullet's momentum is lost? Any remaining momentum in the bullet or bullet fragments, would lead to a lessening of the movement of the head.
EDIT: And even so, the bullet is estimated to have lost over a third of its velocity by the time of impact, so the movement would only less than two-thirds of the stock-against-your-forehead movement. And, if someone were to try this little experiment, there's a good chance that the impact of the rifle stock would blow either the front or the rear of their head out, in a jet like seen in Z313.


quote:
Originally posted by All-American:
If the original momentum of the bullet is too small to move the head, the total momentum of the exiting bullet, skull fragments, and jet of cranial matter must also be too small to move the head. Unless you can show me where momentum (or energy) is being added to the system.

Let's call direction of motion of the bullet "positive", shall we? So before we have head stationary and bullet with positive momentum. After impact, even if the bullet loses no speed (which obviously it really does) we have positive momentum = momentum of bullet + momentum of jet. There needs to be a negative momentum to balance the books. This is found in the backwards motion of the head. The "added" momentum you ask for is the jet itself, which was previously motionless matter. Again, this is how rocket power works... you start with zero momentum (stationary rocket, engine not firing) and end with zero momentum (rocket going one way, hot exhaust gas rushing the other) -- no momentum is "added".

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RoofingGuy
The First USA Noel


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quote:
Originally posted by All-American:

Furthermore, his jet effect calculations contain serious errors which invalidate his entire assertion. He assumed the bullet exited Kennedy's skull intact, whereas in reality it fragmented into hundreds of pieces inside the skull.

But the total momentum of all the fragments, is still equal to the momementum of the bullet prior to fragmentation (minus the momentum equal to the impulse causing fragmenting - which is quite small*), and the centre of gravity of the fragment collection still follows the path of the center of gravity of the intact bullet.


*ETA: The impulse is rather small because it is the product of the force of the skull on the bullet, multiplied by the length of time the skull and bullet are actually in contact... it is nowhere near negligible in this case, of course, but the resulting fragments still had quite a bit of momentum afterwards.

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All-American
Deck the Malls


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quote:
Originally posted by Michael Cole:

From memory, the head jerk was considered as being caused by a muscle spasm in the neck, and actually occurred slightly after the bullet hit.

The neuromuscular contraction theory was first espoused by ballistics expert Larry Sturdivan in testimony before the House Select Committee on Assassinations (HSCA).

At the request of the HSCA, Sturdivan performed experiments firing a Mannlicher-Carcano at human skulls coated with gelatin (to simulate skin) and filled with fluid the approximate density and viscosity of cranial tissue. He was somewhat flummoxed to discover that the skull always moved in the same direction as the rifle bullet. Every single time.

So as an alternative theory, he dug up some old footage of US military tests firing bullets point-blank into the heads of goats. (Yeesh!) The goats, with their heads locked in wooden stocks, exhibited the peculiar behavior of throwing their feet out from under themselves at the moment of impact. Sturdivan postulated that this is what happened with Kennedy.

I doubt this explanation for three reasons:

1. The goat reaction looks little, if anything, like Kennedy's head movement in the Zapruder film. (The goat film is available on the internet at the McAdams website.)

2. Neurologists have since stated that in instances where the brain is completely destroyed, such as Kennedy's was, there is no muscular reaction - the entire body simply goes limp. Remember, Sturdivan was a ballistics expert, not a neurologist.

3. From the Zapruder film, the head motion appears to be a direct reaction to the head shot, not a bodily jerk. Of course, this is just opinion.

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All-American
Deck the Malls


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quote:
Originally posted by The Rubber Chicken:

Penn & Teller do a demonstration of the concept on Season 3 of Bullsh!t. They take a honeydew melon and wrap it in seran wrap or something like that, put it on a pedestal, and shoot it with the same type of rifle that Lee Harvey Oswald used. The melon does indeed fall back towards the direction of the shot, while the melon innards fly forward with the bullet. If I remember correctly, they say their demonstration is actually a recreation of a demonstration done by the Warren Commission when investigating the assassination.

This is why Penn and Teller should not be allowed to have a TV show. [Smile]

Actually, the melon experiment was first performed by Luis Alvarez, in an attempt to validate his jet effect calculations. This was many years after the Warren Commission had folded its tent. The Commission itself never addressed the anomalous motion of Kennedy's head, believing that the public would never get to see the Zapruder film. When the Commission published still black & white photographs taken from the film, the two which showed the head shot were reversed in order, making it appear Kennedy's head moved forward from the impact. I kid you not... [Frown]

Anyway, the infamous honeydew melon experiment is disingenuous from the outset - it's designed in advance to produce the desired results. While it's possible Penn and Teller are too ignorant to know the difference, I find it hard to believe Alvarez wasn't aware his "experiment" used a stacked deck.

In order to produce the reverse motion from the jet effect, just choose a target with three characteristics:

1. The surface should be soft, and easily penetrated by the bullet. This guarantees very little momentum will be transferred from the bullet to the object as the bullet enters.

2. The "skin" should have a very low tensile strength, so that large chunks easily break free as the bullet is exiting.

3. The bullet should be allowed to exit intact.


All three of these elements are present in spades when one fires a rifle bullet at a melon. None of the three are true for a human skull, as Larry Sturdivan found out.

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RoofingGuy
The First USA Noel


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quote:
Originally posted by All-American:

In order to produce the reverse motion from the jet effect, just choose a target with three characteristics:

1. The surface should be soft, and easily penetrated by the bullet. This guarantees very little momentum will be transferred from the bullet to the object as the bullet enters.

2. The "skin" should have a very low tensile strength, so that large chunks easily break free as the bullet is exiting.

3. The bullet should be allowed to exit intact.


All three of these elements are present in spades when one fires a rifle bullet at a melon. None of the three are true for a human skull, as Larry Sturdivan found out.

1) But Alvarez wrapped the melon in one inch of Scotch tape to simulate hard skull, with the melon simulating the inner soft brains.

2) Alvarez wrapped the melon in one inch of Scotch tape to simulate hard skull, with the melon simulating the inner soft brains.

3) The bullet doesn't have to exit at all, let alone intact, for the skull to burst.


An exploding head is why safety helmets have an internal head band -- the bullet (or a blow from anything else) doesn't have to pierce the skull at all to cause a jet to explode outward through the weakest portion, which is usually either the front, the back, or an exit hole from a projectile. The head band in a crash helmet protects the head from the jarring motion; it prevents the shock wave from entering the skull with such force -- it's not there to simply provide ventilation around the head.


ETA: And besides, bone doesn't have all that high a tensile strength -- it's comparable to glass, and less than half that of cotton... and almost identical to adhesive tape. But the work of fracture for bone or melon/tape is really much more important than the actual tensile strength in this particular case.

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RoofingGuy
The First USA Noel


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quote:
Originally posted by All-American:

2. Neurologists have since stated that in instances where the brain is completely destroyed, such as Kennedy's was, there is no muscular reaction - the entire body simply goes limp.

Without going in to the whole mess about autopsy coverup/non-coverup, only the right cerebrum was mostly destroyed, the left cerebrum, the cerebellum, the hippocampus and the spinal cord were intact. If there entire brain was destroyed, then yes, there could be no muscular spasms, but there would have been no respiration or faint pulse on arrival at Parklands.

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I refuse to get into a battle of wits with an unarmed person...

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CaptainWunderpants
I Saw Three Shipments


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Ok, I've watched this thread and read the articles with great interest. My great thanks to Roofing Guy and All-American for their excellent contributions.

I've read the ballistics paper linked by UEL and now understand how a head explodes after being shot.

There is still something I'm not sure on concerning the nature of the "jet". AA covered this already, but I'll go into more detail.

If a bullet enters the back of the skull, and exits the front, accompanied by a jet of brain matter, and the total force going out the front is greater than the total force going in the back, where does the extra energy come from?

i.e. p(momentum) = m(mass) x v(velocity).
Just because there is more mass coming out than going in (bullet + brains versus just bullet) doesn't mean more momentum, as there is a corresponding drop in velocity to balance things out. This holds true if the bullet doesn't exit.

Intuitively, you would think the momentum calculations would run something like this.

Forward momentum p = m(of bullet) x v (taking into account reduction of velocity due to friction).

Reverse momentum p = m(of bullet + brain matter) x v(of bullet and brain matter).

Final momentum = forward p - reverse p, but you would have to take into account energy lost transfers other than kinetic transfer, e.g. heat, sound (possibly very minimal).
Anyway you compute it, without an extra source of energy the final momentum should be forward, if only negligibly.
Of course, this is based on an assumption that it all happens at once, which it clearly doesn't, and the video seems to show two separate acceleration events, but I don't understand how this ultimately changes the final outcome - the head does appear to me to go further back than its starting position.

To ignore this is to violate a certain law of thermodynamics. Of course, it may be that Lee Harvey Oswald stumbled on a perpetual motion machine, even if it is a bit expensive in terms of the number of US Presidents it needs as fuel.

The only thing I can think of that might answer this is if the brain is pressurised - i.e. it contains stored energy that is added to the equation, much like shooting an aerosol can.

I know little of anatomy, but I was of the opinion that the brain is in fact not pressurised.

In short, I don't understand how the facts fit the theory, even for the melon experiment.

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RoofingGuy
The First USA Noel


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CaptainWunderpants: Good question, and I'll try to explain as best as I am able.

If we take the President's body as a frame of reference, so that we don't have to also account for the motion of the car, then before impact the head is essentially motionless, and the bullet has both kinetic energy of 1/2*m*v² and momentum of m*v. After impact, the bullet has undergone a loss of velocity. This lowers the bullet's momentum, but due to the second power, lowers the kinetic energy by more.

Some of the "lost" kinetic energy goes into fragmenting the bullet, and some goes in to fracturing the skull, and some is lost as heat, but most is transferred into the fluid-like brain matter and stored temporarily in the form of a pressure, caused by the shock waves of the impact and of the bullet's passage (and some of this energy-as-pressure comes from potential energy released during fracturing of bone, it's not all from the bullet).

The shock waves in the head bounce around and echo at the speed of sound, but since in this case the bullet was still supersonic*, it has already passed out of the head.

The elasticity of the cerebral matter and the kinetic energy stored as the pressure front are what launch the "jet". So the kinetic energy of the jet can actually be more than the kinetic energy lost by the bullet, since some potential energy is transformed to kinetic.

So the kinetic energy can easily "not add up" if you are only looking at kinetic energy, but in the system as a whole, there is no energy created out of nothing, and no "perpetual motion machine".

Since there were large fragments of skull ejected, along with the brain matter, the mass of the jet is much higher than the mass of the bullet, and the jet/head mass ratio is much higher than the bullet/head mass ratio.

So, although the jet is "high-speed", it is much slower than the bullet. It's momentum is considered "high" due to the high mass, moreso than a truly "high" velocity.

So, to balance the books we have the momentum of the bullet before impact = momentum of bullet after impact (lower) + momentum of jet. But due to the energy transfer systems, and the relatively high mass of the ejecta, the equation doesn't balance. We end up needing a negative momentum because some of the ejecta's momentum has come from stored potential energy, and not from the momentum of the bullet itself. To balance the equation, momentum of bullet before impact = momentum of bullet after impact + momentum of jet - momentum of head.

Momentum is conserved, total energy is conserved (except that lost as heat), and the head moves in the opposite direction to the "jet".


ETA: The energy release on fracture can easily be seen when you snap a piece of uncooked spaghetti. Often a small piece breaks off and flies away with seemingly more energy than what you are adding to the system by applying force (i.e. the piece wouldn't fly so far or so fast if you pushed it with the same force you are applying to the whole). The "extra" energy is released during the creation of the fracture planes. Again, there is no "perpetual motion", just an energy transfer from potential to kinetic.

*ETA: Actually I was in a rush to reply and made a minor goof. The bullet was most likely subsonic as it exited, but, since the speed of sound in both bone and brains is much higher than in air, the bullet (or bullet fragments) was quite dramatically subsonic, not "still supersonic", as it passed through the brain, but that little nitpick doesn't change the fact that the shock waves form and then collapse behind the bullet's path and the bullet is long gone by the time the "jet" starts.

--------------------
I refuse to get into a battle of wits with an unarmed person...

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All-American
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quote:
Originally posted by UEL:

In my career I've had the opportunity to do a lot of ballistic work. Wound ballistics is my weakest area, but a quick google on the words Wound Ballistics turns up this gem of an article.

It is a wound ballistics article discussing Kennedy's fatal shot.

It is a bit technical but, from my limited experience, sound.

Actually, the article is pretty shoddily written. And you can tell him I said so. [Smile]

"For purposes of illustration, assume the final speed to be 400 feet per second. The average speed through the head would then be (1800 + 400)/2, or 1100 feet per second."

"Curiously, however, the second scenario gives the same time of transit as the first scenario, as can be seen by a simple example. Imagine that the bullet instantaneously decelerates by 300 ft s-1 each time it penetrated the cranium. It would then impact at 1800 ft s-1 and reduce immediately to 1500 ft s-1. It would then impact the other cranium wall at 700 ft s-1 and immediately decelerate to 400 ft s-1. Its average speed through the head would then be (1500 + 700)/2, or the same 1100 ft s-1 found for the original scenario. A little thought will convince the reader that no matter how much the bullet decelerates while entering and exiting, its average speed will be 1100 ft s-1. Thus the transit time of 0.5 ms is an invariant number."


Let's ignore the fact that he expresses the deceleration in units of velocity instead of acceleration, and just address what he's trying to say. The only reason the transit time is an "invariant number" is because he sets it up that way. First, he arbitrarily assumes an exit velocity of 400 ft/s with absolutely no justification. Then he changes the decrease in velocity across the cranium to whatever number is required to produce that final 400 ft/s. And then he marvels over how he always gets the same number. [Roll Eyes]

To wit:

When he assumes the bullet "instantaneously decelerates" by 300 ft/s for each penetration of skull bone, he also assumes the intercranial velocity decrease is 800 ft/s. But if we assume the bullet instantaneously decelerates by 200 ft/s for each penetration, his equation is set up so that the intercranial velocity decrease will rise to 1000 ft/s. Instead of (1500 + 700)/2, the numbers become (1600 + 600)/2. There is certainly not an inverse relationship between the loss of velocity through the bone and the loss of velocity through the brain. And his total claim of a 0.5ms transit time is therefore completely unsubstantiated. The author is an idiot. [Smile]

But it gets worse. He claims

"In summary, then, a high-speed bullet striking a head produces two separate motions, an immediate snap in the same direction as the bullet, and a subsequent motion 5-10 milliseconds later, in a direction not predictable but calculable after the fact from the aggregate motions of the fragments ejected by the exploding head."


He's so sure of that 5-10 millisecond number, he states it three times in the article, so we know it's not a typo. What he proves, without realizing it, is that the alleged forward movement of Kennedy's head in the Zapruder film cannot be from the same shot which causes his head to "explode".

Zapruder's camera ran at approximately 18 frames per second. Each frame therefore represents .056 seconds of time, or 56 milliseconds. Actual exposure time for each frame is usually about 1/2 the total frame time (with the other half being used to advance the film to the next frame).

The supposition is that Kennedy's head jerks forward in frame 312 of the Zapruder film, one frame before it explodes. Detection of this jerk is allegedly made by comparing his head position in frame 312 relative to frame 311. (I say "allegedly" because I'm not convinced it even truly exists.) So the "rear shot" must have impacted Kennedy's head between frames 311 and 312. But the head burst isn't seen until frame 313, meaning the time period that frame 312 was being exposed (28 milliseconds) is the minimum time between the supposed rear head strike and the head explosion.

This proves:

A. By the author's own numbers, the head explosion could not have been caused by the alleged head shot between frame 311/312.

B. The Zapruder film would be physically incapable of recording the alleged head shot and subsequent explosion as two separate events.

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All-American
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quote:
Originally posted by RoofingGuy:

1) But Alvarez wrapped the melon in one inch of Scotch tape to simulate hard skull, with the melon simulating the inner soft brains.

2) Alvarez wrapped the melon in one inch of Scotch tape to simulate hard skull, with the melon simulating the inner soft brains.

3) The bullet doesn't have to exit at all, let alone intact, for the skull to burst.

Are you saying the bullet's ability to penetrate a skull is equivalent to it's ability to penetrate Scotch tape?

The bullet most certainly does have to exit the skull for the jet effect to work. If not, when it's stopped inside the head, all of it's forward momentum will be transferred to the head. Any motion will be in the direction of the bullet travel.

quote:
An exploding head is why safety helmets have an internal head band -- the bullet (or a blow from anything else) doesn't have to pierce the skull at all to cause a jet to explode outward through the weakest portion, which is usually either the front, the back, or an exit hole from a projectile. The head band in a crash helmet protects the head from the jarring motion; it prevents the shock wave from entering the skull with such force -- it's not there to simply provide ventilation around the head.
Um... what? [lol] The head band keeps the head from exploding? Really?


You're actually arguing a cause that's already lost. It's already been proven in a laboratory environment, by an impartial investigator, that a human skull will not exhibit the jet effect:

From Larry Sturdivan's testimony before the HSCA

Mr. STURDIVAN - The skull was, as I said, the dried skull, obtained from a biological supply house, was filled with gelatin tissue simulant and the shiny effect on the outside is a coating of gelatin on the outside of the skull. To the left is a piece of goat skin simulating the scalp and hair. I will run right through the first one which is rather dramatic, and I will stop action on the second skull [describing second skull impact]. The bullet has come in from the left, has impacted the skull through the scalp simulant and is now within the skull. As you can see, the radial velocity that is imparted at the first part of the track has begun to crack the back piece of the skull. This is the very next frame. It shows the fragmented bullet and fragments of the skull being blown away from the front of the skull.

Mr. MATHEWS - The bullet is gone now; is that correct?

Mr. STURDIVAN - Pieces of the bullet have exited the skull. It is hard to tell whether they have actually gone out of the frame or whether they may be incorporated into that white mass which is mostly bone with a little bit of gelatin tissue simulant in it. As you can see, the radial velocity has already begun to fracture the skull extensively along and across suture lines. As you can see, each of the two skulls that we have observed so far have moved in the direction of the bullet. In other words, both of them have been given some momentum in the direction that the bullet was going. This third one also shows momentum in the direction that the bullet was going, showing that the head of the President would probably go with the bullet. This is amplified, however, in these skulls because they are not tied to a human body. They are free to move from the table. Also, you will see that as the skull goes forward, some of the material of the skull and the contents were blown out toward us. Consequently, the opposing momentum carries the skull away from us, rotates it away from us so that we can actually see the bottom part of the skull in this shot. In fact, all 10 of the skulls that we shot did essentially the same thing. They gained a little bit of momentum consistent with one or a little better foot-per-second velocity that would have been imparted by the bullet and they also lost material toward us, that is, toward its right and, therefore, rotated toward its left.


So, should we discuss what happens when a bullet penetrates a real human skull, or shall we focus our attention on watermelons?

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All-American
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quote:
Originally posted by RoofingGuy:

The elasticity of the cerebral matter and the kinetic energy stored as the pressure front are what launch the "jet". So the kinetic energy of the jet can actually be more than the kinetic energy lost by the bullet, since some potential energy is transformed to kinetic.

No it can't. Are you trying to say the inside of a human head is under pressure? Any "potential energy" created by stretching the cranium is equal to or less than the kinetic energy lost by the bullet. Period. Else we're back to Captain Wunderpants' perpetual motion machine.

quote:
...because some of the ejecta's momentum has come from stored potential energy, and not from the momentum of the bullet itself.
Again, no. There is no "stored potential energy". The melon motion can be and is explained simply by two facts:

1. The force required for the bullet to enter and exit the melon is lower than the force required for the bullet to move the whole melon. Hence, the melon does not move in the direction of the bullet.

2. Because of the geometry of the melon, and its low tensile strength, considerably more material is carried away when the bullet exits than when it enters. This is for the same reason that drilling through a piece of wood produces a round hole on the entrance surface and splinters on the exit surface, and why dams are always built so their convex surface faces upstream. The ejection of melon pieces causes the melon to move in the opposite direction. There is no "stored potential energy", nor is more energy released than was carried in by the bullet.

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RoofingGuy
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Ok, AA, let's go step by step...

First you say
quote:
Let's ignore the fact that he expresses the deceleration in units of velocity instead of acceleration,
yet in your quoted sections he never does so, he only refers to a change in velocity (not a change over a specified time):
quote:

The average speed...

...decelerates by 300 ft s-1 each time...

...reduce immediately to 1500 ft s-1....

...immediately decelerate to 400 ft s-1...

He never claims to be giving decelerations, just what the change in speed is. If you are driving at 65mph and hit the brakes and decelerate to 25mph, that is proper wording. You are not giving the deceleration as 40mph, you are giving the change in speed due to decelerating as 40mph.

You then say:
quote:
First, he arbitrarily assumes an exit velocity of 400 ft/s with absolutely no justification.
And yet the article said:
quote:
Assuming the bullet entered the head moving at 1800 feet per second, as proposed by the Warren Commission, and exited with sufficient speed to dent the inside of the limousine’s windshield and the chrome strip above it, its final speed might still have been hundreds of feet per second. For purposes of illustration, assume the final speed to be 400 feet per second.
The article you are quoting from is an overview of the theory and the math... the actual calculated exit velocity in the other 38 chapters of the same article is 200ft/s.

I'm also not quite sure how you find a problem with you choosing 200ft/s instead of 300ft/s for the loss through bone. Isn't (1500+700)/2 = (1600+600)/2 ?? Don't they both come to 1100? Isn't that why he calls it an invariant number? Won't the change in velocity always be invariant once you've chosen starting and ending points for purposes of illustration? If the loss through bone goes down from 300 to 200, and the loss through cranial matter thus goes up from 800 to 1000 isn't that an inverse relationship? It's not proportional, but I always thought that was what "inverse" meant -- one goes up, the other goes down.

You then say:
quote:
The supposition is that Kennedy's head jerks forward in frame 312 of the Zapruder film, one frame before it explodes. Detection of this jerk is allegedly made by comparing his head position in frame 312 relative to frame 311. (I say "allegedly" because I'm not convinced it even truly exists.) So the "rear shot" must have impacted Kennedy's head between frames 311 and 312. But the head burst isn't seen until frame 313, meaning the time period that frame 312 was being exposed (28 milliseconds) is the minimum time between the supposed rear head strike and the head explosion.
I've never seen anyone claim this... the comparisons are made between Z312 and Z313. Somewhere between Z312 and Z313 the bullet strikes. The forward motion is always noted between Z312 and Z313, not between Z311 and Z312. This is why the timing doesn't work for you. The Warren Comission found the bullet to hit between Z312 and Z313. I find no sites (either "consipracy" sites, or sites defending the Warren Commission) that claim the head is struck between Z311 and Z312 with the head moving forward between these two frames.


Then:
quote:
Are you saying the bullet's ability to penetrate a skull is equivalent to it's ability to penetrate Scotch tape?
No, that's not what I said at all... read again... you ignore the other engineering and structural aspects of the whole matter, and focus on the tensile strength of skull vs. melon skin. I then point out that the scotch tape "skull" the melon had has the same tensile strength as bone. According to your science, Alvarez' experiment should exactly model a human skull.

As to:
quote:
The bullet most certainly does have to exit the skull for the jet effect to work. If not, when it's stopped inside the head, all of it's forward momentum will be transferred to the head. Any motion will be in the direction of the bullet travel.


Um... what? [lol] The head band keeps the head from exploding? Really?

Please allow me to quote from prof. J.E. Gordon's The New Science Of Strong Materials in the section on "Impact Strength" (pg 102 of 2nd edition)

quote:
...
When a shell is fired against armour plate, if the shell does not penetrate, then what is known as a "scab", a jagged piece of armour, sometimes becomes detached from the inside or back surface. If this happens, the scab may bounce about with great speed and energy within the turret and may do as much damage as if the shell had actually penetrated.

In a similar way, when a projectile is fired into a tank of liquid, such as the fuel tank of an aeroplane, it is the exit hole which is much the largest and the most difficult to seal since the shock waves which are readily transmitted through the fluid may burst the back of the tank. Unfortunately the human head is structurally rather like a tank of liquid and the consequences when it is struck by a bullet are well-known. What is less well-known is that rather similar effects may happen with a blow on the forehead which does not penetrate. The important factor in the design of crash-helmets is therefore the cushioning of the shock wave so as to prevent damage at the back of the skull. This is the reason for the internal head-band in helmets which looks as if it was put in in order to provide ventilation.

Italics added by me. In both the airplane case and the head case, the bullet doesn't have to exit (or even enter) for the shock wave to burst an "exit hole".

You then remark:
quote:
You're actually arguing a cause that's already lost. It's already been proven in a laboratory environment...
But wait... could there possibly be a reason that engineering and materials books list completely different properties for live bone, sinew, muscle, skin, etc.. and for dead samples? Using a "dried skull" must automatically reproduce the exact behavior of a living head, despite such variations in physical properties, right?


quote:
So, should we discuss what happens when a bullet penetrates a real human skull, or shall we focus our attention on watermelons?
Well, thanks for the snark, but as I pointed out in the Gordon quotation, I was discussing the true reactions of human skulls to various blows, whether penetrating or not.

--------------------
I refuse to get into a battle of wits with an unarmed person...

Posts: 724 | From: Ontario, CAN | Registered: Jan 2005  |  IP: Logged | Report this post to a moderator
RoofingGuy
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AA, you keep saying:
quote:
There is no "stored potential energy".
Again, let me quote from prof. Gordon, this time from Structures, pg 92

quote:
All elastic substances which are under load contain greater or less amounts of strain energy, and this strain energy is always potentially available for the self-destructive process which we call 'fracture'.
So, when the bullet tip first starts to press on the skull, before any cracks can form in the bone, the bullet is straining the bone and storing potential energy in the bone, despite how many times you deny its existence.

Again from Gordon:
quote:
The sixty-four thousand dollar question whether the structure actually breaks at any particular juncture depends on whether or not it is possible for this strain energy to be converted into fracture energy so as to create a new crack.
Since the bone can elastically store more energy than is eventually needed to fracture it, there is a release of energy when fracture occurs, just like in my spaghetti example.

ETA: And again, the shock waves from the blow and from the bullet's passage are pressure differences in the material, be it solid, liquid or gas, and a difference in pressure is potential energy, no matter how many times you insist otherwise.

ETAA: And the reason the potential energy released can be more than the kinetic energy lost, is that there already is stored strain energy (and chemical energy in the bonds which must be broken for fracture) in the bone, before new strain energy is added by the bullet. There still is no "perpetual motion" problem. Breaking chemical bonds releases potential energy -- look at TNT.

--------------------
I refuse to get into a battle of wits with an unarmed person...

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RoofingGuy
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Back to the "dried skull" example, for a moment...

Seeing as how the dried bone has completely different values for Young's modulus, tensile strength, compressive strength, etc... that is precisely why Sturdivan's experiments do not show the described behaviour. The dried bone doesn't have the same strain energy characteristics and energy-transfer characteristics, and is considerably more brittle. His experiments were designed (either purposefully, or from lack of engineering) to not show what live bone reacts like. The same energies aren't stored upon impact, so are not subsequently released. Sturdivan mentions small pieces of bone ejecting in both directions, but not the large (4"+) chunks of bone that were blown from Kennedy's head due to the shock waves.

So, ironically, Alvarez' Scotch tape is a closer model to the true behaviour, from a materials and structures (i.e. engineering) perspective.

--------------------
I refuse to get into a battle of wits with an unarmed person...

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NobbyNobbs
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quote:
Originally posted by RoofingGuy:
It's all conservation of momentum... you take a small projectile moving at high speed, and collide it with a stationary, much larger target, and the target's momentum hardly changes... and even less so if the projectile exits and keeps on travelling.


Not to nitpick, but it is not true that the target's momentum hardly changes at all. In fact, it changes by *exactly* the amount that the bullet's momentum changes. That's what conservation of momentum is all about.

What you meant to say is that the *velocity* of the target barely changes. This is due to its larger mass. Momentum is the product of mass and velocity. Shoot that bullet at an apple, the apple changes velocity quite a bit. Shoot it at a barn, the barn hardly changes velocity at all. It's all due to relative mass.

This has nothing at all to do with your other points. Just wanted to clear up some semantics.

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Back in the days before electricity, we were forced to watch TV by candlelight.

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RoofingGuy
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quote:
Originally posted by NobbyNobbs:
What you meant to say is that the *velocity* of the target barely changes.

I understand your semantic issue about the conservation of momentum, and the bullet's loss is exactly equal to the target's gain. The bullet loses some velocity and momentum, the target gains some velocity and some momentum. I was thinking "target velocity hardly changes/change in momentum is barely noticible" (due to the much larger mass, as you rightfully point out) but ended up typing "momentum hardly changes".

Thanks for keeping me honest [Big Grin]

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I refuse to get into a battle of wits with an unarmed person...

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The Rubber Chicken
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quote:
You're actually arguing a cause that's already lost. It's already been proven in a laboratory environment, by an impartial investigator, that a human skull will not exhibit the jet effect
Not exactly. Dr. Olivier, during the Rockefeller Commission, used the same procedure that Dr. Sturdivan used, and added this caveat:

"The skulls that we shot invariably rolled away from the gun. And this was a reason for this, that you didn't get any jet effect, because the gelatin that we used was 20 percent gelatin, this was our simulant for tissue. We also used it as a simulant for the brain.

There is one bad thing about that. If you want to see this movement, the gelatin is too elastic, it recovers, in other words, any gelatin that expands out comes back like a rubber band. So it didn't fly loose from the skull to get a jet effect. "

Emphasis mine. Thus, it is not clear that the gelatin used is any better a simulation of human tissue -- if testing for the jet effect -- than a melon.

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