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Re: Effect of Moon on balance?



I wrote:

The gravitational pull of the Moon cannot be measured on the Earth using a
balance; precision of the balance has nothing to do with it.
The Earth is in free fall toward the common center of mass in the Earth-Moon
system.

John Denker wrote:

That might be true if the earth were pointlike. But it's not.
The "center" of the earth is in free-fall toward the center of mass, but your
laboratory is not.
Tides are easily detectible. http://www.monmouth.com/~jsd/physics/tides.htm

Yes, I can see that (excellent web page!). But my question was: is it possible
to measure changes of gravitation force due to Moon
when you have:

-- a laboratory somewhere on the Earth
-- constant conditions (e.g. density of air which may affect buoyance etc.) in
the laboratory
-- very precise balance
-- object of known mass on the balance

So all other things being equal: would the *balance reading* in the laboratory
vary in time due to change in relative position of the Earth and Moon?
My answer is no. Should I change my opinion?

Regards,

Antti

Antti Savinainen
Senior Lecturer in Physics and Mathematics
Kuopion Lyseo High School
Puijonkatu 18
70110 Kuopio, FINLAND
E-mail: antti.savinainen@kuopio.fi
Personal web page: http://kotisivu.mtv3.fi/oma/physics/