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

One of the helpful references in this thread pointed to the Autodesk proprietor's science web site.
Though he has the usual boring Republican line on the "Liberal media", he shows a splendid setup
with a step ladder, to which a short length of 6lb rated nylon monofilament is tied, secured by a
bridle to a lath of foam insulation with a lead fishing weight placed at each end.
Beneath the lath is fixed a blade of thick aluminum foil cut from a cooking tray which dips
in a can of water on the floor as a damper.

The most esoteric item of the setup, of which he shows time lapse video, is the room location
- a basement store room set in a limestone stratum which provides a rather stable temperature.
The experiment is observed with a web cam and a video camera to avoid drafts.

The cost might run to $5 plus cameras. He warns that the suspension must relax for 2 or 3 days
before it will be stable. (The nylon he used can easily be replaced with a stiffer polyester tape
or VHD polyethylene line or tape, no doubt.)

Brian W

On 10/28/2010 11:00 PM, 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!