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Re: [Phys-l] How did Newton estimate the Gravitational constant?

It's actually not so hard to _demonstrate_ Fg attraction with a crude torsion balance built of junk using a VHS tape suspension; the _real_ difficulty is getting good measurements. I had a student replicate
a balance apparatus described at
and videotape quite successfully overcame the endless spinning relaxation you must endure with twine or monofilament.

The student was quite bemused with standing still for about 5min near the apparatus; he could deflect the balance arm with himself.

Dan M

Dan MacIsaac, Associate Professor of Physics, SUNY-Buffalo State College
222SciBldg BSC, 1300 Elmwood Ave, Buffalo NY 14222 USA 1-716-878-3802
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Physics Graduate Coordinator ON SABBATICAL Fall 2010 / Spring 2011

Fall 2010 Visiting Scholar
Helsingin yliopisto 224 Physicum, Kumpula Campus
Gustaf Hällströmin katu 2a FI-00560 Helsinki

On Oct 29, 2010, at 7:00 AM, Bernard Cleyet wrote:

BTW, Stong's Amateur Scientist (Sci. Am. Sept. '63)

gives instructions for a Mitchell torsion balance; it's large -- suspension 55" (#36 music wire**) arm, 41" weights (masses) 46 oz. juice can lead filled, and 100 gm. Both cylindrical -- like the recent rather more accurate one using W. Spheres are best, but diff. to accurately machine, no?

** I remember reading another one using 1/4" mag. tape.

bc notes included an electrostatic shield -- much larger constant!

On 2010, Oct 28, , at 10:39, Bernard Cleyet wrote:

Yes, and I think credit should be given to Michell who made the beta version of the balance and gave it (indirectly) to C. just before he (Michell) died.

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