Re: Oddities of Physics!


dave wrote:
> On 22 Aug 2005 05:44:02 -0700, "Henry Lemington-Wholeflavors"
> <cwocwocwo@xxxxxxxxxxx> wrote:
>
> >
> >dave wrote:
> >> On Mon, 22 Aug 2005 10:14:22 +0100, Palindr?me <sb382638@xxxxxxxxxxxxxxxxxxx>
> >> wrote:
> >>
> >> >>>
> >> >>>
> >> >>> Strictly speaking, heavier objects fall faster than lighter objects
> >> >>> even in a perfect vacuum, but the reason for this is slightly subtle,
> >> >>> and in most cases could be ignored.
> >>
> >> Really! Can you tell us what the error in time would be between say a 1Kg ball
> >> of lead and 0.1kg of lead falling 1m in a vacuum at sea level (on Earth)? ie
> >> expand the "subtle" bit.
> >
> >I could,
>
> Then how about showing us then?
>
> >although it would be vanishingly small for those masses.
> >There's not even anything like GR envolved here - just Newtonian
> >mechanics. I'm surprised no-ones got the reason why yet.
>
> I don't really care much whether you are surprised or not - but genuinely
> interested - I'm not trying to take the p (not on this occasion anyway.) :-)
>
> Clearly from your "those masses" comment it has to do with relative masses ie a
> huge and a tiny. Anyway, enlighten us. I'm not afraid to be educated.

It only really matters when the mass of the object that's falling is an
appreciable percentage of the mass of the object it's falling towards,
but it would still apply to your 1Kg and 0.1 Kg lead weights, albeit in
a minute, hair-splitting, infinitesemally small way.

If, for example, an asteroid falls towards Earth, it's acceleration
will be proportional to the mass of the Earth, and obviously also to
1/r^2, where r is the inter-centre-of-mass distance.

But, of course, the gravitational force the Earth exerts on the
asteroid is exactly the same as the gravitional force the asteroid
exerts on the Earth (but opposite in direction), and the Earth will
itself experience an acceleration, this time proportional to the mass
of the asteroid, causing 1/r^2 to increase quicker the greater the mass
of the asteroid is.

.

Relevant Pages

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