[time-nuts] Pendulums & Atomic Clocks & Gravity
Didier Juges
didier at cox.net
Sun May 27 21:30:18 EDT 2007
Ulrich,
From NASA: http://map.gsfc.nasa.gov/m_mm/ob_techorbit1.html
<quote>
More precisely, the *Lagrange Points* mark positions where the
gravitational pull of the two large masses precisely equals the
centripetal force required to rotate with them.
</quote>
I am in good company :-)
(except that I used the term "centrifugal" instead of "centripetal")
Didier KO4BB
Ulrich Bangert wrote:
> 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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>
>
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