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Re: [Phys-l] Gravity?

Jim,

Is the pull of the whole earth the integrated sum of gravitation force terms from collection of infinitesimal mass elements that constitute the earth. I.e. Int (G m dM /r^2 * (-r_hat)) ?

I guess I'm really asking what do you mean by "the pull of the whole Earth"; I need to know that before I would agree that g is the free-fall acceleration of an object near the surface of the earth.

Joel

_________________________

Joel Rauber, Ph.D 
Professor and Head of Physics
Department of Physics
South Dakota State University
Brookings, SD 57007
Joel.Rauber@sdstate.edu
605.688.5428 (w)
605.688.5878 (fax)


-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of Espinosa, James
Sent: Thursday, November 18, 2010 11:29 AM
To: Forum for Physics Educators
Subject: [Phys-l] Gravity?

Joel, g is still the free-fall acceleration of bodies near the surface
of the Earth, which istself is due to the pull of the whole Earth. I
only assume Newton's Laws of Motion and a state of Equilibrium to derive
N = mg. My students understand it. Try avoiding the use of "weight"
when students constantly hear or read about "losing weight."
Individuals leaning against the wall require friction and horizontal
forces for equilibrium; I do not consider such, only vertical forces.

James Espinosa
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