[time-nuts] Pendulums & Atomic Clocks & Gravity

Bill Beam wbeam at gci.net
Sat May 26 17:06:10 EDT 2007

On Sat, 26 May 2007 13:34:24 -0700, Brooke Clarke wrote:

>Hi Bill:
>It's my understanding that a satellite is in free fall, hence zero g.

'Free fall' implies that g is not zero!

If g=0 was true, then the satellite would not be falling at all.
It is beacuse g is not zero, that the satellite is in 'orbit' rather
than moving off in a straight line.

Jumping off a cliff also is "free fall" and surely g is not zero.
The only difference between the cliff jumper and a satellite
in orbit is the satellite never reaches the ground.

The rate of a clock does depend on g.

Now a pendulum clock in orbit has infinate period, but not because
g is zero. This is because the pendulum support point is also
in orbit.  This is no different than pushing a pendulum off a cliff.

A pendulum swings back and forth because two forces act on
the bob.  One of the forces is mg and the other is the force of
the pendulum support rod.


>Of course there's a gravitational field at the location of the satellite, the 
>one from Earth being the largest.  Orbital mechanics gives me a headache so 
>let's hear from someone more knowledgeable.
>Have Fun,

Bill Beam

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