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

From: Peter Richards <pedrichards_at_meteoritecentral.com>
Date: Wed, 6 Mar 2013 15:37:22 -0600
Message-ID: <CAENymwAZvGDANzL+V1xAn5rihs2Y8gBHkh8wZrq1Dg2LtXWxVA_at_mail.gmail.com>

       To preface this, I'll let you know: I have dealt with some
persons who such questions have been, rather, "over the head of," (pun
not intended)... one of whom seemed to settle on the theory that I
must be hurting my brain with too much thinking, and another who was
satisfied with a conclusion to a variation of the forthcoming problem
based on the idea that sand blows to the northeast U.S. from the
"midwest" region, while larger stones do not (not that these persons
are professional physicists, thankfully). Maybe this would be better
directed at a physicist, but since I am dealing with something which
pertains to meteorites, and certain specific falls, I will submit this
for consideration by the members of this list:
      On earth, acceleration of a suspended, then falling, or dropped,
object, such as from a standstill, is determined by the mass of the
object in a positive respect and the factor of air resistance in a
negative respect; hence, a denser material of the same shape and
orientation falls faster. This is because, here on earth, we have both
an atmosphere, and a specific directional pull of gravity. I've read
that, on the moon, where resistance of the atmosphere is negligible,
if not absolutely nil, two objects of unlike densities will be pulled
downwards at an equal rate (they say, even an elephant and feather
will be pulled downward at the same rate, only being resisted by
gravitational pull from other objects in the universe, I figure). If
those observations are correct (and I'm not entirely sure they,
although, it seems as if they very well may be, to me), then we've
identified two situations, 1. one in which mass and density with
relation to shape/and orientation does matter, but sum shape/volume
(short for what determines air resistance) does not, for if an object
is twice the size of the other, although not twice as dense, but an
equal density, and shape, and orientation, it will fall at the same
rate, because the ratio between its own mass and air-displacing
profile is equal (I am not saying this law is universal, at all
scales, but for practical purposes maybe it is?), and 2. another, in
which, shape and orientation don't matter, and nor does the mass, or
the density .
     So, finally, my question is this: Do we have a third situation in
which mass and density has a negligible effect, but air resistance due
to shape and orientation does (That is to say, compensating for
gravitational pull correlating to mass, or in a vector in which this
is negated, the objects would encounter particles travelling at
them.)? Again, it's somewhat difficult to imagine, but if there were
such a scenario, would a large heavy object, NOT be held more still
than a proportionally lighter and smaller object, but RATHER less so?
Hence, for a fourth time, would higher inertia be totally detached
from correlating to higher mass, thus correlating only with lower air
resistance, ie better aerodynamics?
     One might think that a bolide does not fit these criteria (or
support this thesis), since the larger, generally less aerodynamic
pieces tend to travel farthest, but is this not a result of these
particles having been subject to less air resistance, in sum, than the
smaller particles, which had broken from the outer surfaces of these
very objects, due to the very momentum the "main masses" carried, in
effect, absorbing the shock for them, somewhat (meaning they it is not
for lack of momentum, due to lower mass, that they end up travelling
less far)?

(a question of) Peter Richards
Received on Wed 06 Mar 2013 04:37:22 PM PST