**Next message:**Robert J. Bradbury: "Re: Paths to the Singularity"**Previous message:**Joe E. Dees: "Re: Phenomenology [unintentional]"**In reply to:**Spike Jones: "Re: Cooling technique for Jupiter brains"**Next in thread:**Spike Jones: "gimps and the singularity again"**Reply:**Spike Jones: "gimps and the singularity again"**Reply:**Damien Broderick: "Re: On the razor-sharp Ginrummy Arithmetic of Death"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]

Gee Whillikers, Spike, you use kitchen arithmetic better'n... well, I

can't say that, on account of the little'uns. But you're a pro, make no

mistake about it. "Me 'at's off to the Duke!" I always used 90 minutes,

so my numbers were always off. Now I see why. D'oh! :)

Spike Jones wrote:

*> If you are in a boring meeting and need to derive the mass of the
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*> earth, one need only remember the orbit time of 85 minutes, and it
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*> can be backed out with only that information. The lowest satellites
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*> take a little longer, since they need to be a couple hundred km above
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*> the deck so they dont get dragged down immediately by the atmosphere.
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*>
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*> There is another way, if you need the earth's mass to only one
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*> digit of precision: you know the volume of a sphere is 4/3pi*r^3,
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*> but for single digit accuracy, pi~3, so V~4*r^3, and you know
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*> that the km was initially proposed as 1/10,000 the distance from
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*> the equator to the pole, so the radius of the earth can be calculated
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*> to be 10,000/pi*2~6370 km. Cube that and quadruple it, and the
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*> volume of the earth comes out to close enough to 1E12 km^3, and
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*> since the density of iron and nickel are in the 8000 kg/m^3 range
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*> and granite and other rocky stuff is in the 4000 range, then assume
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*> an average density of about 6000 kg/m^3 and you get an earth
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*> mass of 6E24 kg, which is quite close enough.
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*>
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*> >From that, knowing that a 1 kg mass weighs a force of 9.8 newtons,
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*> one can calculate the universal gravitation constant without having
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*> any reference material handy, assuming you remember that
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*> F=GMm/R^2, since you know F, M, m and R.
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*>
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*> But I digress. {8-]
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**Next message:**Robert J. Bradbury: "Re: Paths to the Singularity"**Previous message:**Joe E. Dees: "Re: Phenomenology [unintentional]"**In reply to:**Spike Jones: "Re: Cooling technique for Jupiter brains"**Next in thread:**Spike Jones: "gimps and the singularity again"**Reply:**Spike Jones: "gimps and the singularity again"**Reply:**Damien Broderick: "Re: On the razor-sharp Ginrummy Arithmetic of Death"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]

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