[time-nuts] Pendulums & Atomic Clocks & Gravity
Brooke Clarke
brooke at pacific.net
Sat May 26 13:17:55 EDT 2007
Hi:
Just starting to adjust the bob on a pendulum clock, see:
http://www.prc68.com/I/SWCC.shtml
and doing some calculations regarding the pendulum. Which soon leads to the
value of "g". This can be found for U.S. locations using an on line calculator
at: http://www.ngs.noaa.gov/cgi-bin/grav_pdx.prl (need Lat, Lon, elev)
Then a pendulum calculator at:
http://www.ajdesigner.com/phppendulum/simple_pendulum_equation_period.php
allows solving any of 8 pendulum related equations.
Tom has pointed out that the stability limit on pendulum clocks is in the area
of 1E-7 because of the complex effect of the Sun and Moon on the value of "g".
http://www.leapsecond.com/hsn2006/ch1.htm
Gravity also effects atomic clocks, see: http://www.leapsecond.com/great2005/
and this puts a limit on what can be done with any atomic clock that's on
Earth. "g" will always have minor fluctuations (noise) due to all sorts of
things like the Sun, Moon, planets, asteroids, earthquakes, etc. It's still a
direct "g" effect called red shift like (U2 − U1)/c2, where the Us are
gravitational potentials, only smaller by c squared.
I expect that in not too many years the official master clocks will no longer
be on Earth, but instead in satellites. There "g" is precisely known to be
zero. Since GPS satellites are excellent for time transfer that's where they
will be. The ensemble will be the full constellation.
In "Time Too Good to Be True" Kleppner
http://www.physicstoday.org/vol-59/iss-3/p10.html
says "...a primary standard in space would not overcome the problem of
comparing time or frequency at different locations on Earth."
I don't understand why that would be the case with a standard in a GPS
satellite. Granted E-18 can not now be done using the current GPS system, but
when atomic clocks get into the E-16 or better area and are in satellites, I
think the quality of time transfer will keep up.
Just an idea & Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com
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