What physics reveals about the JFK event

[Andrew Mason]

  I never said the conservation of momentum and the jet effect are two different principles but rather that they are antagonistic to one another in the given circumstance at hand There are indeed two competing variables. Lets use the illustration of a head shot where no exit wounds or blood splatter of any meaningful amount exits the skull. In such a situation we can conclude the force of the bullet has been absorbed, or if you prefer the language of the physicist, transferred to the skull. The transference of the that force occurs both in terms of internal damage to the skull and the the movement of the skull and body in accord to the law of conservation of momentum

Momentum is conserved regardless of how much damage occurs. If the bullet does not exit the skull and no matter exits the skull then the momentum of the head + bullet will be equal to the momentum of the bullet immediately prior to the bullet contacting the head (assuming the head is able to move independently from the body). 
 

It looks like Tony Szamboti focuses on the major error behind Alvarez's equation here


The temporary
cavity pressure generated in the wake of a projectile’s path through an encased fluid filled
volume is not directly related to the shock wave momentum forward of the projectile in the
way the forward acting pressure of a jet engine is related to the momentum of its exhaust.

I am not sure what the point is.  The pressure in front of the bullet is built up by the bullet pushing matter forward toward the front of the skull. A jet engine take incoming air from the front, builds up the pressure inside the engine by compressing that air and adding heat and then expelling it out the back. What matters is the pressure and volume of matter inside just before the matter exits.

[Matt Grantham]

Momentum is conserved regardless of how much damage occurs. If the bullet does not exit the skull and no matter exits the skull then the momentum of the head + bullet will be equal to the momentum of the bullet immediately prior to the bullet contacting the head (assuming the head is able to move independently from the body). 
 I am not sure what the point is.  The pressure in front of the bullet is built up by the bullet pushing matter forward toward the front of the skull. A jet engine take incoming air from the front, builds up the pressure inside the engine by compressing that air and adding heat and then expelling it out the back. What matters is the pressure and volume of matter inside just before the matter exits.

 Nope a car crash is a perfect example of how kinetic energy/force is transferred into damage to the vehicle and momentum is lost

[Andrew Mason]

Nope a car crash is a perfect example of how kinetic energy/force is transferred into damage to the vehicle and momentum is lost

Nope. Kinetic energy is transferred into damage to the vehicle but momentum cannot be lost.  Momentum is always conserved. Conservation of momentum is among the most fundamental laws of physics.  A car crash is an example of an inelastic collision where kinetic energy is lost due to the damage (but not momentum).  A collision of two billiard balls is an example of an (almost) elastic collision where kinetic energy is retained as is momentum.   Momentum is NEVER lost in any kind of collision. See: http://hyperphysics.phy-astr.gsu.edu/hbase/elacol.html

[Matt Grantham]

Nope. Kinetic energy is transferred into damage to the vehicle but momentum cannot be lost.  Momentum is always conserved. Conservation of momentum is among the most fundamental laws of physics.  A car crash is an example of an inelastic collision where kinetic energy is lost due to the damage (but not momentum).  A collision of two billiard balls is an example of an (almost) elastic collision where kinetic energy is retained as is momentum.   Momentum is NEVER lost in any kind of collision. See: http://hyperphysics.phy-astr.gsu.edu/hbase/elacol.html

 Likely there is a linguistic misunderstanding of some sort here but when a car hits a wall damage occurs and momentum is lost. Or momentum is transferred into the structures that are transformed into damage if you prefer

[Andrew Mason]

Likely there is a linguistic misunderstanding of some sort here but when a car hits a wall damage occurs and momentum is lost. Or momentum is transferred into the structures that are transformed into damage if you prefer

The wall is attached to the earth.  Although it is not perceptible due to enormous mass of the earth, the earth's momentum increases.  The total momentum of the car + wall/earth are the same before and after the collision.  Kinetic energy is generally not conserved in collisions but momentum is always conserved.  Momentum cannot disappear.  It does not matter how or how much energy disappears as heat in the collision. In fact, if it is a collision where one body collides with another and the two bodies end up being stuck together, we can use the conservation of momentum to determine the final speed of the bodies and, thereby, determine exactly how much kinetic energy was lost in the collision.

The bottom line: If the bullet strikes the head and matter is ejected from the head, that ejected matter carries momentum and the remaining part of the head must gain an opposite amount of momentum such that the total momenta of the head matter and bullet are the same before, during, and after the impact.

[Matt Grantham]

  Matt said

                          In such a situation we can conclude the force of the bullet has been absorbed,


   There is no mention of momentum in this statement. So lets talk in terms of kinetic energy and force unless there is a problem with that?

[Andrew Mason]

  Matt said

                          In such a situation we can conclude the force of the bullet has been absorbed,


   There is no mention of momentum in this statement. So lets talk in terms of kinetic energy and force unless there is a problem with that?

If you want to discuss physics you have to use terms that have clear physical meaning.  While force and kinetic energy are well understood terms (F = ma; KE = mv^2/2), the concept of "absorbing a force" is not at all clear. You will have to explain what that means.

[Matt Grantham]

If you want to discuss physics you have to use terms that have clear physical meaning.  While force and kinetic energy are well understood terms (F = ma; KE = mv^2/2), the concept of "absorbing a force" is not at all clear. You will have to explain what that means.

 Indeed and if you are to switch terms you too should be clear. I have already explained that absorbing force is simply the transference of kinetic energy into the damage of structures. Did you miss that? Or if you like it another way, the resistance a given substance has to a  force, in this case a projectile. The pedantic posturing here seems a bit hollow for anyone who is yet to cite anything concrete in terms of the jet theory