Would A Bullet Really Knock You Backwards? DEBUNKED

[Dan O'meara]

So long as one offers a plausible mechanism to explain the body's motion and so long as there is no evidence at all of a shot from the front right, that is all one needs.  Introducing an uncertain mechanism to explain the body's motion is just giving fuel to the conspiracy fanatics. 

I don't see how the feet being jammed under the front seat helps prove that there was a neuromuscular spasm.  There is nothing to show that JFK did not put his feet there before the shot. There was not a lot of room between the seats.  That would be especially so with Connally in front because he was quite tall and he would likely have pushed the seat back as far as it would go.  Besides, wouldn't a push of the body upward from the feet push the feet down?

The recoil from the exploding head provides a mechanism based on the evidence of what we can actually observe (matter driven out of the head at high speed).  The mechanism of a neuromuscular spasm due to catastrophic loss of brain matter from the right side (which controls the left side of the body) does not have sufficient basis in fact.  It may be possible but we really can't say it occurred.  We can, however, say based on what is observed in the zfilm, that the head received a left-rearward impulse from the matter exploding out of the front right side of his head.

The recoil from the exploding head provides a mechanism based on the evidence of what we can actually observe (matter driven out of the head at high speed).

I don't think you understand what the so-called "jet effect" entails.
Do you believe that the momentum  of any matter traveling away from the head has an equal and opposite impulse on the head?
Do you believe that when the bullet fragments exit the head they have a recoil effect on the head?

[Andrew Mason]

The recoil from the exploding head provides a mechanism based on the evidence of what we can actually observe (matter driven out of the head at high speed).

I don't think you understand what the so-called "jet effect" entails.
Do you believe that the momentum  of any matter traveling away from the head has an equal and opposite impulse on the head?

First of all, it is not about belief. This is demonstrated, repeatable, measurable,  physical science: Newton's laws of motion.

If matter experiences a change in motion, there must be a force acting on it for a period of time (Newton 1). That force multiplied by time integrated over the period of its duration is the impulse or change in momentum it experiences.(Newton 2).

But forces are always paired (Newton 3). So if matter changes its momentum by experiencing forces for a period of time, another body must experience an equal but opposite force for the same period of time and, therefore, an equal and opposite change in momentum.(Newton 3).

So it is not about matter travelling away from the head. It is about matter experiencing a change in motion. The matter ejected from the head experienced a change in its motion due to a force supplied by other matter in the head from which it was ejected.  Therefore, that other matter-the remaining head - experienced an equal and opposite change in momentum.

 

Do you believe that when the bullet fragments exit the head they have a recoil effect on the head?

The laws of physics apply. If the bullet experiences a change of momentum while in contact with matter, that matter experiences an equal and opposite change in momentum. If the matter was the head, the head experiences a momentum change that is equal in magnitude and opposite in direction to the change in momentum of the bullet.

If the bullet experienced an increase in its forward momentum in passing through the head, which seems unlikely, but possible, it would impart some recoil momentum to the head. For example, if the bullet came to a stop in the head and then exploded out of the head due to the built-up pressure in the head and the skull opening up, this would occur.

If the bullet passed through the head and just slowed down, the change in momentum of the bullet is opposite to its direction of travel (ie. toward the shooter). So the head would experience a change in momentum that is equal and opposite to the change in bullet momentum (ie. forward, away from the shooter). In that case, the bullet fragments do not experience any increase in forward momentum on leaving the head so the head does not experience any increase in rearward momentum (recoil). This is, perhaps, the more likely of the two possible scenarios.

[Dan O'meara]

First of all, it is not about belief. This is demonstrated, repeatable, measurable,  physical science: Newton's laws of motion.

If matter experiences a change in motion, there must be a force acting on it for a period of time (Newton 1). That force multiplied by time integrated over the period of its duration is the impulse or change in momentum it experiences.(Newton 2).

But forces are always paired (Newton 3). So if matter changes its momentum by experiencing forces for a period of time, another body must experience an equal but opposite force for the same period of time and, therefore, an equal and opposite change in momentum.(Newton 3).

So it is not about matter travelling away from the head. It is about matter experiencing a change in motion. The matter ejected from the head experienced a change in its motion due to a force supplied by other matter in the head from which it was ejected.  Therefore, that other matter-the remaining head - experienced an equal and opposite change in momentum.

 The laws of physics apply. If the bullet experiences a change of momentum while in contact with matter, that matter experiences an equal and opposite change in momentum. If the matter was the head, the head experiences a momentum change that is equal in magnitude and opposite in direction to the change in momentum of the bullet.

If the bullet experienced an increase in its forward momentum in passing through the head, which seems unlikely, but possible, it would impart some recoil momentum to the head. For example, if the bullet came to a stop in the head and then exploded out of the head due to the built-up pressure in the head and the skull opening up, this would occur.

If the bullet passed through the head and just slowed down, the change in momentum of the bullet is opposite to its direction of travel (ie. toward the shooter). So the head would experience a change in momentum that is equal and opposite to the change in bullet momentum (ie. forward, away from the shooter). In that case, the bullet fragments do not experience any increase in forward momentum on leaving the head so the head does not experience any increase in rearward momentum (recoil). This is, perhaps, the more likely of the two possible scenarios.

The matter ejected from the head experienced a change in its motion due to a force supplied by other matter in the head from which it was ejected.  Therefore, that other matter-the remaining head - experienced an equal and opposite change in momentum.

What was the "force supplied by other matter in the head"?
What force did the remaining head use to eject matter?
Where did this force come from?
Because it's not the bullet.
You are saying the remaining head provided a force that ejected the jet of material.
How was this force provided?

[Andrew Mason]

The matter ejected from the head experienced a change in its motion due to a force supplied by other matter in the head from which it was ejected.  Therefore, that other matter-the remaining head - experienced an equal and opposite change in momentum.

What was the "force supplied by other matter in the head"?
What force did the remaining head use to eject matter?
Where did this force come from?
Because it's not the bullet.
You are saying the remaining head provided a force that ejected the jet of material.
How was this force provided?

The force was provided by pressure that was built up inside the head by the bullet and suddenly released. 

We know that there was pressure built up because the skull opened up and matter exploded out of the head in wide directions.  We can see that in the zfilm.

As you know, the bullet passing through tissue creates a temporary cavity around it.  But in a head, there is no ability to expand the volume.  The brain, like water, is almost incompressible so a very small compression of volume increases the pressure tremendously.  So the energy deposited in the head builds up pressure.  When that pressure is released by the rupturing of the skull (likely initiated by the bullet exiting through the front of the head) matter is propelled out of the opening from the tremendous force (pressure x area).

If the pressure increase was just one atmosphere (1 bar or just over 100 kPa or 100,000 N/m^2) and the area of the skull that opened up was (estimating the size of the opening) was, say, 10 cm x 10 cm (4"x4") or .01 m^2, the total force on the matter expelled (force=Pressure x area) would have been 1000 N. if the matter expelled was 400 grams or .4 kg, then the acceleration would have been:


a=F/m=1000/.4= 2500 m/s².


So in 10 ms. or 1/100th of a second, the speed would have been v=at=2500/100=25m/s  That represents a momentum change of .4 x25 = 10 kg m/s and an equal and opposite momentum change to the head.  Since the total incoming bullet momentum was .01g x 610 m/s =6.1 k m/s, the momentum of the recoiling head exceeds the maximum forward momentum imparted by the bullet. So head goes backward.

[John Mytton]

I think it was a combination of elements that created the back and to the left motion.

Kennedy's back brace stopped him from falling forward.




The jet effect drove him backwards.



And I also agree with Joe's thread opener that a penetrating bullet simply lacks the kinetic energy to throw anyone anywhere.

Mythbusters fired a 50 cal bullet into a steel plated dummy with no penetration and it barely moved.
Also in the following video, a firing squad shoots multiple men and they just drop down and virtually all of them fall back towards the shooters.

@ 0.37

JohnM

[Andrew Mason]

I think it was a combination of elements that created the back and to the left motion.

Kennedy's back brace stopped him from falling forward.



The jet effect drove him backwards.

Great clips of jet-effect.  I will add Chad Zimmerman's turkey shoot:

And I also agree with Joe's thread opener that a penetrating bullet simply lacks the kinetic energy to throw anyone anywhere.

Again it is not about insufficient kinetic energy.  The bullet has more than enough kinetic energy to throw a body.  A .01 kg bullet at 610 m/s has kinetic energy of .005 x (610)^2 Joules = 1860 Joules.  A 100 kg body recoiling at 1 m/s has only 50 Joules of kinetic energy (mv^2/2) or only about 2.5% of the bullet energy..   What is lacking is the mechanism to convert bullet energy into motion of the body.  Jet effect is a rather crude energy converter and uses a small fraction of the bullet kinetic energy.  But the jet effect can impart significant momentum as your clips show - more than the incoming bullet if enough matter explodes from the body.

Suppose a 1800 Joule bullet could be "caught" by a mechanism that compresses a spring in a 100 kg body as the bullet slows down so that the kinetic energy of is all transferred to the spring. The release of that spring against a fixed wall, say, would cause the 100 kg body to be thrown at a speed of:  v= √{2E/m}= √36=6 m/s

[John Mytton]

Great clips of jet-effect.  I will add Chad Zimmerman's turkey shoot:

Again it is not about insufficient kinetic energy.  The bullet has more than enough kinetic energy to throw a body.  A .01 kg bullet at 610 m/s has kinetic energy of .005 x (610)^2 Joules = 1860 Joules.  A 100 kg body recoiling at 1 m/s has only 50 Joules of kinetic energy (mv^2/2) or only about 2.5% of the bullet energy..   What is lacking is the mechanism to convert bullet energy into motion of the body.  Jet effect is a rather crude energy converter and uses a small fraction of the bullet kinetic energy.  But the jet effect can impart significant momentum as your clips show - more than the incoming bullet if enough matter explodes from the body.

Suppose a 1800 Joule bullet could be "caught" by a mechanism that compresses a spring in a 100 kg body as the bullet slows down so that the kinetic energy of is all transferred to the spring. The release of that spring against a fixed wall, say, would cause the 100 kg body to be thrown at a speed of:  v= √{2E/m}= √36=6 m/s

The bullet has more than enough kinetic energy to throw a body.

Of course you are right, I should have said that the amount of movement would be limited to an inch or two, just like we see in the Zapruder film and the Mythbusters clip.

JohnM

[Joe Elliott]

The force was provided by pressure that was built up inside the head by the bullet and suddenly released. 

We know that there was pressure built up because the skull opened up and matter exploded out of the head in wide directions.  We can see that in the zfilm.

As you know, the bullet passing through tissue creates a temporary cavity around it.  But in a head, there is no ability to expand the volume.  The brain, like water, is almost incompressible so a very small compression of volume increases the pressure tremendously.  So the energy deposited in the head builds up pressure.  When that pressure is released by the rupturing of the skull (likely initiated by the bullet exiting through the front of the head) matter is propelled out of the opening from the tremendous force (pressure x area).

If the pressure increase was just one atmosphere (1 bar or just over 100 kPa or 100,000 N/m^2) and the area of the skull that opened up was (estimating the size of the opening) was, say, 10 cm x 10 cm (4"x4") or .01 m^2, the total force on the matter expelled (force=Pressure x area) would have been 1000 N. if the matter expelled was 400 grams or .4 kg, then the acceleration would have been:


a=F/m=1000/.4= 2500 m/s².


So in 10 ms. or 1/100th of a second, the speed would have been v=at=2500/100=25m/s  That represents a momentum change of .4 x25 = 10 kg m/s and an equal and opposite momentum change to the head.  Since the total incoming bullet momentum was .01g x 610 m/s =6.1 k m/s, the momentum of the recoiling head exceeds the maximum forward momentum imparted by the bullet. So head goes backward.

I'm not certain I agree with these calculations. But putting this aside, you say that after 10 ms, the head started to move backwards. If so, how is it, that according to the study by Physics Graduate Student William Hoffman, in his work for Josiah Thompson for the book "Six Seconds in Dallas" measured JFK's head at frame 313, two inches, or 5 cm, forward of the 312 position, by frame 313?

Why did the head immediately, or almost immediately (after just 10 ms) start moving backwards, and yet ended up 2 inches forward?

Provide me with a possible scenario. Don't use the excuse "Well, we can't tell exactly what happened". Just give us a possible scenario. That would be good enough.

We can use the following time system. z312.0 is when the shutter opens on frame 312. z312.5 is when the shutter closed on frame 312.

So, I need to see something like the following:

z312.5 - the bullet strikes.
during z312.5-z312.7, the head moves forward 2.5 inches, or 6.25 cm, at a rate of 12.5 mph.
z312.7 - the head explodes and the head starts moving backwards, at a rate of 0.6 inches per frame, or about 0.6 mph.
z313.5 - the head has moved back to a position where the head is 2.0 inches ahead of the position in frame 312.

This scenario is clearly impossible, for the bullet to push the head forward at 12.5 mph.

But what possible scenario, not a scenario you can 'prove', but a possible scenario, that would allow the head to start moving backwards after 10 ms, and still have the head 2 inches ahead of it's frame 312 position by the time the shutter closed at frame z313.

So, to summarize:


Questions:

Is there a possible scenario that fits the William Hoffman data?

Is this scenario in accordance with Classical Physics?

Is so, what is that scenario?