Can you see the quick forward snap?
One of the most critical pieces of evidence in the entire JFK assassination
is the quick forward snap of JFK's head immediately as he was hit in the head.
This movement proves that the head shot came from the rear. (See "Wound
Ballistics.") Unfortunately, the snap is a subtle motion that is best seen by
rapidly alternating between Zapruder frames 312 and 313 on a laserdisc or DVD
player. But it can also be seen in these images from J. Masland's web site
"Nook of Eclectic Enquiry" (http://www.jmasland.com
). If you put your
eyes close to the screen and rapidly move up and down between these two images,
you can see for yourself how JFK's head bends forward between 312 and 313. Focus
on the back of his neck and watch the angle change. Actual measurements on
black-and-white enlargements made from Life's color original negatives
showed that the back of JFK's head moved forward about three inches (Josiah
Thompson, Six Seconds in Dallas).
From the three inches of snap and the time between the frames (1/18.3 sec),
it is a simple matter to calculate the average forward speed of the head.
Combining the (estimated) mass of the head with the speed gives the forward
momentum of the head, which can them be compared with the momentum of the
incoming bullet from Oswald's rifle. If the two numbers are compatible, that is,
if the momentum of the head is a little smaller than that of the impacting
bullet, the snap is compatible with being caused by the bullet. This is exactly
how the numbers work out. (See "Physics of Head Shot.") Since we also
know that the two big bullet fragments found in the limousine's front seat came
from Lee Harvey Oswald's rifle to the exclusion of all other rifles, our working
hypothesis must be that the killing bullet was fired from Oswald's rifle. Given
that there is no strong evidence against this view, its probability of being
true is high indeed.
(Thanks to John Masland at "Nook of Eclectic Inquiry" for these images.)