Physics and the frontal hit that never was

16 February 2003

    From 1994 through 1997 I spent a lot of time trying to quantitatively understand JFK's double response to the fatal head shot, the original topic that drew me into the JFK assassination. By "double response," I mean the quick forward snap (that is now conveniently ignored by most writers) and the longer, slower rearward lurch, the only movement seen when the Zapruder film is viewed at full speed. My goal was to see which of these movements was compatible with the Mannlicher-Carcano bullet that hit the rear of JFK's head, exited in pieces from the front right side, and then went on to hit the windshield and possibly also fly over the top and hit James Tague or the curb near him.
    I was struck by the fact that this problem could be approached, at least in principle, by combining the basic physics of colliding bodies with some principles of wound ballistics. I was also surprised that no one seemed to have done this either qualitatively or quantitatively. I began simply, with the forward snap, and learned quickly that its speed was fully compatible with the Carcano bullet and reasonable exit velocities. I then combined the rearward motion, the real goal of the work, with the forward snap and learned that the former was also compatible with the known hit. In the process, I generated seven simulations, each of increasing complexity, separately for translational (linear) and rotational (angular) motions, for 14 simulations in all. I ended by adding an eighth simulation for angular motion and a treatment of some of the major errors that could render some of my conclusions suspect.
    Along the way, I tried to present a summary of this work at two JFK conferences, COPA in 1997 and Lancer in 1998. COPA toyed with the paper and then declined it because I refused to tell them precisely what my conclusions were going to be. (I followed standard scientific practice and submitted an abstract of the type they requested, but no more. This smacked of censorship to me, and was an eye-opening experience.) I then submitted a similar abstract to JFK Lancer's meeting in Dallas. Their program chairman George Michael Evica effectively pocket-vetoed that abstract by refusing to act one way or the other on it until it was too late. That was another eye-opening experience. The two experiences jointly showed that the JFK community was not interested in serious discussion of the possibility that the prime piece of evidence for conspiracy, JFK's rearward lurch, might actually have been a physical effect of a shot from the rear. Talk about being closed-minded!
    In 1997 I had to put this work aside and turn to other things. Only in November 2002, five years later, did I find myself with enough time to begin to prepare an Internet version of it. I have greatly expanded it, and am posting it in detail so that others may judge the data, calculations, reasoning, and conclusions as fairly as possible. Rational comments are always appreciated, particularly on points that appear weak. I can be reached at krahn@uri.edu or kenrahn@kenrahn.com .
    This monograph addresses four basic questions:

1. Can the forward snap be accounted for by a rearward shot from Lee Harvey Oswald's rifle? Answer: Yes, with ease.
2. Can the initial rearward lurch of head and body be accounted for by a rearward shot from the same rifle? Answer: Yes, with ease.
3. Must a rearward shot from this rifle have created a rearward lurch similar to that observed? Answer: Yes, provided only that a cloud of brain matter was thrown forward.
4. Can a shot from the grassy knoll explain or contribute to the rearward lurch? Answers: No; qualified yes.

The answers effectively debunk the notion of a frontal hit and thereby remove the major piece of evidence for conspiracy in the JFK assassination.
    The questions are addressed by the 39 chapters of the monograph shown below.

Abstract

Setting the stage

1. Introduction
2. The Zapruder film: movements to be explained
3. The physics of colliding and exploding objects
4. Wound ballistics and physics
5. Variables and values

Question 1: Can the forward snap be explained by a shot from Oswald's rifle?

6. The forward snap—linear calculations
7. The forward snap—angular calculations

Question 2: Can the rearward lurch by explained by a shot from Oswald's rifle?

8. Plausibility analysis of the rearward lurch
9. Lurch 1 Linear—simplest analysis, with bullet, body, and cloud
10. Lurch 2 Linear—adds large fragments
11. Lurch 3 Linear—adds conical 3-D motion of cloud
12. Lurch 4 Linear—adds 3-D motion of large fragments
13. Lurch 5 Linear—adds 3-D motion of body
14. Snap/Lurch 6 Linear—adds four time intervals and solves for v_cloud
15. Snap/Lurch 7 Linear—adds four time intervals, sets v_cloud, and solves for PE
16. Lurch 1 Angular—rotational analog of Lurch 1 Linear
17. Lurch 2 Angular—rotational analog of Lurch 2 Linear
18. Lurch 3 Angular—rotational analog of Lurch 3 Linear
19. Lurch 4 Angular—rotational analog of Lurch 4 Linear
20. Lurch 5 Angular—rotational analog of Lurch 5 Linear
21. Snap/Lurch 6 Angular—rotational analog of Snap/Lurch 6 Linear
22. Snap/Lurch 7 Angular—rotational analog of Snap/Lurch 7 Linear
23. Summary of solutions and most important variables

Question 3: Must the rearward lurch be explained by a shot from Oswald's rifle?

24. Introduction to the built-in constraints
25. Preconstraining with m_head, d_snap, t_lurch, and v_frags
26. Constraints on Θ_cl and PE
27. Constraints on m_cloud and v_cloud from Θ_cl vs. m_cloud
28. Constraints on m_cloud and v_cloud from Θ_cl vs. PE
29. Constraints on m_cloud and v_cloud from m_cloud vs. v_cloud
30. Grand summary of constraints

Question 4: Can the rearward lurch be explained or contributed to by a frontal shot?

31. Introduction to a frontal hit
32. Scenario 1—no cloud or large fragments
33. Scenario 2—cloud and fragments as observed
34. Scenario 3—frontal hit right after rear hit
35. Scenario 4—rear hit provides only snap
36. Summary of the frontal scenarios

Synopsis

37. The unification of the physical evidence provided by these calculations
38. Objections and replies
39. Future work

Acknowledgments

Additions and Corrections