On 12/4/2018 5:35 PM, John Clark wrote:
Brent Meeker wrote:
> / finding the value of G depends on scaling the result by that
ratio of masses (1.37e25 lbm/348 lbm). /
The mass of the Earth played no part in Cavendish's determination of G
because he was measuring gravitational attraction in a direction that
was parallel to the Earth's surface.
But in comparing it to the clock precision you have to consider that the
clock is measuring the change over a cm of a very much greater
potential, while Cavendish is measuring a much smaller change in a much
smaller potential.
/The way you are looking at consider how far you would have to
move the cesium clock from the surface of the 348lbm cannon ball
in order to detect the change in gravitational time dilation
affecting the clock. /
OKlets look at it like that, the new clock can detect the difference
in time dilation between 1g and 1.000000003g, so I'm sure it could
detect the time dilation caused by a 348 pound mass a foot or so away.
Could it? The gravitational time dilation factor is tau = sqrt[1 -
2GM/rc^2]. So a clock that can detect a one cm change in height at the
Earth's surface is in fact not accurate enough to to detect the
difference between being adjacent to a 348lbm 18" ball and being
arbitrarily far away from it.
But .000000003gis so weak a force it would not have caused Cavendish's
torsion balance to move at all, air resistance and the rigidity of the
wire holding it up would have prevented it.
The description I read of Cavendish's experiment said the smaller masses
were 9" from the cannon balls.
/> It's the number I cited, far bigger than the 0.25mm Cavendish
cited as the limit of his measurement./
There is no way Cavendish could have placed the centers of two
248pound lead balls 0.25mm apart, lead just isn't that dense.
No, 0.25mm is his estimate of the smallest change in deflection he could
detect. The weights on his torsion balance were 9" from the cannonballs
center, which I assume was the radius of his cannon balls since the
measurement would be most accurate when the torsion weights were nearest
the cannon balls.
Brent
John K Clark
--
You received this message because you are subscribed to the Google
Groups "Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send
an email to [email protected]
<mailto:[email protected]>.
To post to this group, send email to [email protected]
<mailto:[email protected]>.
Visit this group at https://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/d/optout.
--
You received this message because you are subscribed to the Google Groups
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at https://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/d/optout.
