Hi Tom: I get it. It's really "g" that matters and not the force (F = m * g).
Have Fun, Brooke Clarke http://www.PRC68.com http://www.precisionclock.com Tom Van Baak wrote: >>Then a pendulum calculator at: >>http://www.ajdesigner.com/phppendulum/simple_pendulum_equation_period.php >>allows solving any of 8 pendulum related equations. > > > Note that this simplistic l/g formula does not characterize the > period of precision pendulum clocks, as it ignores factors > such as circular error, and a host of other static and dynamic > corrections. But it should be good enough for your SWCC. > > >>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 > > > You'll enjoy ch2 and ch3 too; when they're ready... > > >>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 think 99.999% the Moon and Sun. You can ignore all other > objects. True, mathematically, any object of any mass has a > non-zero effect on g, but if you do the tide calculations even > something as massive and as "close" as Jupiter is so far down > in the noise (a few millionths the effect of the moon) that we > don't worry about it for delta g calculations. > > >>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. > > > No, g isn't zero at all. Remember g is inverse square to the > distance from Earth. The other way to think about it is that > satellites wouldn't be (free-fall orbiting) satellites if g were > zero, eh? > > >>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. > > > I believe the point he is making is that time/frequency on earth > is dependent on altitude. Altitude is both a function of place and > of time (e.g., time of day, time of month, as in tides). And since > altitude is wiggling up and down by fractions of a meter (due to > earth tides) you have a real time transfer problem down in the > 18th decimal place. > > By analogy, how do you ultra-precisely measure the elevation > of a lake when there are winds, waves, or ripples? Now think > about ripples on the space-time pond. > > If you want more references on tides, let me know. > Also, related, here's a humbling four-part paper on: > > What Does Height Really Mean? > http://www.aagsmo.org/resources.htm > > /tvb > > > > _______________________________________________ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts