>>Some years ago, I read that the forces necessary to make a fast
>>moving meteoroid have a visual directional change of any kind will
>>immediately destroy it. George Zay
Wouldn't that be an overly generalized statement, with it's application here? There are enough examples of what looks like, sounds like and feels like "zig zag" (such as the Pasamonte example posted) appearing trails to show it is not completely true.
But the overstatement certainly has some truth in it as well under other conditions. As the bolide spirals or gradually zig zags, odds are that it it sloughing off non-ablated material as it goes along. I would guess that that is the tossed material is specifically at the pressure points which cause the zig zaging to begin with, and from the meteor's point of view is like being hit along the edges with a hammer.
Meteorites recovered on earth are almost always made much smaller than the incoming body principally by this destructive action - right?, and not by smooth ablation which I have no references for, but would suppose accounts for not much more than several centimeters depending on composition and momentum as well. The exceptions are the well oriented pieces.
In studying the changing of direction -"zig zagging"- it is probably important to consider that these changes in direction are cycles are slipped into gradually, not instantly, allowing a much greater disippation of energy. In other words, like the puttering jalopy sounds I mentioned, the entire cycle takes place over seconds, and in the Pasamonte example as well as the one I have researched, the clever choice of words of the Australian witness as "gradual zig zags" which are very noticable, is caused by a rock that spins or tumbles at a relatively gentle rate given the situation, and with each tiny advance in time the overall sheer pressure the rock experiences is basically continuous - tangentially increasing or decreasing in a sense. Should the rock quickly flip or not loose enough momentum, then it might explode in a major way - like Pasamonte eventually did, captured right at that moment after zig zagging, which so enchanted Nininger.
It is worth adding that in space visual changes of direction at meteoritical speeds thankfully are possible, with no problem (Cassini orbital insertion, etc.). Undoubtably your old reference was for meteorite entry into the lower atmosphere. Taking into consideration the exponential nature of the mass distribution (scale height) of the atmosphere, it seems clear that ablation processes dominate meteorites traveling straight as an arrow would (ie, parabolically), removing "cosmic velocity" until the atmospheric soup gets thick and sloughing begins to takes over from ablation for most convient sized meteors. So the zig zagging would be most likely beginning after the initial loss of much momentum, at the lower most visual altitudes for meteors that are interestingly enough most probable to survive as meteorites.
As an after thought, a meteorite which is still smoking and glowing somewhat, creating a smoke trail, at say 1000 miles per hour, that weighs 100 pounds still only needs only a negligable force applied perpendicular to it's entry angle (and moreover, it could be downward) to zig zag. A very noticable zig in the velocity vector, since cosine of up to 8 degrees is over 99% conserved and only affects the momentum (or energy) in this corresponding little bit. Just like a man on a swing really going at it can be pushed laterally by a small child and do (quickly damped by other forces) zig. Or a batter in baseball doesn't even feels the tipping of a fastball yet it goes over the Catcher's head.
And finally, the nice photos - and wood carvings - which appear to have famous bolide families traveling in straight lines - like Peekskill or Newark on Trent. But a good question in those cases, is why they all aren't colinear...clearly something has happened at quite high speed that allowed a change of direction up or down which appreciable-sized fragments survived. There may be a counter argument that they started out as a group. I don't believe that for the majority of those cases. I can't believe small objects in space have much chance of stayying so close together after millions of years. Then there are always the bolides that hit earth at cosmic velocities and manage to "skip" off the atmosphere. It is hard to buy that they hit at perfecty tangents, and the one from California 8 years ago only broke in two - and you know it was going fast as I believe it practically completed one orbit...
Saludos
Doug
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