# [time-nuts] Pendulums & Atomic Clocks & Gravity

Ulrich Bangert df6jb at ulrich-bangert.de
Sun May 27 13:59:22 EDT 2007

```Didier,

> gravitational forces, so do objects in Lagrange points. These points
> represent areas where the centrifugal forces compensate for
> gravity....

I am almost sure that this will again produce me a lot of trouble in
answering a lot of people but the idea that there are centrifugal forces
which compensate for gravity are one of the BIGGEST misconcepts that one
may have in physics at all although it is quite common and you may find
statements like that eben in (bad) physics textbooks.

Centrifugal forces are so called fictitious forces which are only
observed from within accelerated systems. Normal physics is done in
inertial systems. In an inertial system consisting of earth and an
satellite there are only TWO forces available: The gravity force by
which earth attracts the satellite and the gravitational force by which
the satellite attracts earth. They are of the same magnitude but of
opposite direction. That is the reason why the "sum of forces" is zero
for the closed system consisting of earth and satellite. There is no
place for any other force like centrifugal or so because there is no
counterforce available that would make the sum of forces zero i case a
centrifugal force would exist. In case you like to discuss it a bit
please go on but be prepared that I will to blow your arguments into
little bits. A good idea to start with is to look after what Newton's
first law is saying about the behaviour of a body for which all forces
compensate each other. Is that what a satellite does???

73 Ulrich, DF6JB

> -----Ursprüngliche Nachricht-----
> Von: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Didier Juges
> Gesendet: Sonntag, 27. Mai 2007 16:54
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] Pendulums & Atomic Clocks & Gravity
>
>
> For the same reason that a satellite in free fall is still subject to
> gravitational forces, so do objects in Lagrange points. These points
> represent areas where the centrifugal forces compensate for
> gravity from
> two objects instead of one for a regular satellite. The only
> way to be
> free from gravitation is infinite distance from mass, until someone
> actually invents the famous gravitational shield :-) I hope
> it comes in
> spray form...
>
> Didier
>
> Neville Michie wrote:
> > Look up Lagrangian points on Wikipedia.
> > There are points of zero gravitational force, about our planet. What
> > is more, these points are stationary with respect to Earth, so
> > Doppler effects would be zero.
> > As the distance from Sun to Earth to Moon varies through
> the year it
> > follows that the distance from Earth of these points must
> vary on a
> > small scale.
> > These points are good for satelites as the orbit never decays.
> > cheers, Neville Michie
> >
> >
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```