[meteorite-list] Physics Questions (Having to Do, Theoretically, with Bolide Trajectories)

From: Peter Richards <pedrichards_at_meteoritecentral.com>
Date: Fri, 15 Mar 2013 00:43:56 -0500
Message-ID: <CAENymwAZ2=2nSTSqKEczjr3B888=6-MGXMc7neJWfoDyAFbo-w_at_mail.gmail.com>

Chris Peterson said: "[re: a falling body]...How the body behaves
depends on the drag force,
which is proportional to the product of the coefficient of drag, the
square of the body's aerodynamic cross section, the density of the air,
and the square of the velocity. The cross section and the coefficient of
drag are related to the size and shape of the body. Mass is not part of
determining the force of drag, and therefore density isn't, either.
However, if there are unbalanced forces (because the body hasn't reached
its terminal velocity) there will be an acceleration that is dependent
on mass (A = F / m , per Newton's Second Law)... The meteor has only a
single significant
force acting on it, drag. Its behavior can theoretically be understood
by considering its mass and the force of drag (since this involves mass,
size, and shape, density is a factor)...[re: particles in free fall,
subject to wind] the smaller, less massive bodies are moved more than
the
larger, more massive ones"

The following hits on my question: Why is drag not dependent on mass
in the former situation described by Mr. Peterson, but dependent on it
in the latter?
It seems that the reason larger fragments tend to travel farther may
be because the compressed air coming off those more massive fragments
provides extra resistance, as the air "funnels" to fill the void
created behind the "bolide" (if that's the correct term), which
retards the progress of the less massive, and less voluminous
(assuming these are relatively homogeneous in material properties as
many meteorites seem to be) particles which have fragmented from that
main mass. Note that this increased pressure, in theory, played a role
in the original fragmentation of the bolide. Hence, according to this
theory, it would be the larger volume dictating the greater "swept"
area of "liquid" atmosphere, ie. air, that dominates the smaller
particles (due to adjacency), rather than the "momentum" garnered from
the mass. I had considered that these bolides might be under the sway
of a force similar to gravity, although, that doesn't explain a
particle which is ejected from a body, due to an impact, as many
meteorites are, which would be propelled, and, for the most part,
relying on maintaining that "escape velocity," and, of course, it
would mean they would have been accelerating a noticeable amount, as
if falling, in those vectors other than that depending on earth's
gravitational pull, and subject to some huge gravitational pull.
(Although maybe they are accelerating toward, say, the sun, but
seemingly that pull is not understood to be a hugely significant
factor... cf/ http://abyss.uoregon.edu/~js/glossary/meteor.html). So,
basically I have offered an explanation as to why bolides/meteoroids
may act as they do, which would suggest they are typically propelled,
and have momentum, but behaviour which is not comparable to that of a
falling body, specifically in those vectors apart from that created by
the pull of the earth. What this, also, may suggest is that the winds
affecting the particles during the "dark flight" stage affect the more
massive particles more drastically. To return to my first sentence on
this topic, unlike rocks laying on the ground, the fluid atmosphere is
moving, so although these more massive bodies have a higher velocity,
if what Mr. Peterson has said about surface area, in a free fall,
being dominated by the greater mass of a relatively homogeneous body
is true, and, consequently, a greater drag, these drag/resistant
forces acting upon them would be subject to the wind as would be their
larger volumes, wind forces analogous to the drag forces described as
being independent of mass, again, in theory.
Thoughts? Rebuttals? Is my question at all understandable?

Peter Richards
Received on Fri 15 Mar 2013 01:43:56 AM PDT