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

From: Michael Mulgrew <mikestang_at_meteoritecentral.com>
Date: Wed, 6 Mar 2013 13:48:41 -0800
Message-ID: <CAMseTy0Onv1BGWgLYD-rf-D0vK-bOWWHZ5iv6CJzcOOEcdRYOw_at_mail.gmail.com>

Peter, when an object is dropped from rest on Earth its mass has
nothing to do with its acceleration. Drop two objects of differing
mass (but similar aerodynamic properties) and they'll both hit the
ground at the same time; this is physics 101. I didn't read past that
part of your post because I figured the rest of whatever you were
trying to reason out would be flawed since your initial understandings
were in error.

Michael in so. Cal.

On Wed, Mar 6, 2013 at 1:37 PM, Peter Richards <pedrichards at gmail.com> wrote:
>
> 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
> ______________________________________________
>
> Visit the Archives at http://www.meteorite-list-archives.com
> Meteorite-list mailing list
> Meteorite-list at meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list
Received on Wed 06 Mar 2013 04:48:41 PM PST