> -----Ursprüngliche Nachricht----- > Von: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Im Auftrag von Didier Juges > Gesendet: Montag, 28. Mai 2007 13:53 > An: [email protected] > Betreff: [time-nuts] FW: Pendulums & Atomic Clocks & Gravity > > > Ulrich, > > I am quite familiar with the cannon analogy. If I may use > this analogy too, please consider the following: > > There must be a force balancing the force of gravity, > otherwise the satellite would not cease from accelerating > under gravity alone. > > Gravity exerts a force on the satellite which tends to make > it fall towards earth. This is the Centripetal force. Inertia > due to the mass of the satellite makes it resist this motion, > and the tangential speed makes it miss the earth. > Centrifugal force is the name we give to that resistance. > When the satellite is in a stable orbit, it does not > accelerate because both forces exactly balance each other. > For the reason you pointed out, in a closed system the sum of > forces must be zero, so there must be a force balancing the > gravity force. So I see we agree. > > If there was no rotation, that force would not exist and the > satellite would accelerate (under gravity alone) towards earth. > > Dont be confused by terminology. The terms centrifugal and > centripetal are just names given to other forces, not actual > forces by themselves. The centripetal force is due to gravity > (but is could be electromagnetic, or anything else. In a > centrifuge, it would be the force exerted by the rotating > arm), the centrifugal force is due to mass, radius and speed. > > 73, > Didier KO4BB > > -----Original Message----- > From: Ulrich Bangert [mailto:[EMAIL PROTECTED] > Sent: Monday, May 28, 2007 5:03 AM > To: 'Didier Juges' > Subject: AW: [time-nuts] Pendulums & Atomic Clocks & Gravity > > Didier, > > I am an physicist, not an engineer. > > Let me use an experiment of thought that Bill Hawkins has > already used in the discussion: Assume an cannon mounted in > an certain height with the barrel mounted tangetial to > earth's surface. Fire an bullet and see it fall to earth > after an certain time of flight. Now use more gun powder and > see the the bullet fall to earth later. Use a BIG amount of > powder and see the bullet leave earth's gravity completely. > Between the > extremes: Drop to surface and leaving earth's gravity > completely there is one powder loading that brings the bullet > into an circular orbit at the height of the cannon. The > bullet never stops to "fall" to earth. However the motion > towards earth's cencer is compensated by the fact that an > tangential motion ALSO means to depart from the center of the > body that you move tangential to. > > 73 and my best regards > Ulrich, DF6JB > -----Ursprüngliche Nachricht----- > Von: Didier Juges [mailto:[EMAIL PROTECTED] > Gesendet: Montag, 28. Mai 2007 02:02 > An: [EMAIL PROTECTED] > Betreff: Re: [time-nuts] Pendulums & Atomic Clocks & Gravity Ulrich, > > Please go ahead, I am all ears... (in all seriousness, I am > not a physicist, just an engineer) > > If earth attracts the satellite and the satellite attracts > earth, how come the satellite and earth don't get together? > What is keeping them apart? > > When you say the gravity forces are of opposite direction, > this is correct. The gravity applied by earth to the > satellite causes a force vector directed towards the earth, > the gravity applied by the satellite to earth is a force > vector of equal magnitude and directed from earth to the > satellite. The external result is null (as a system, there is > no "loss" of force, action = reaction). > > The same holds true for centrifugal forces. The satellite > affects the orbit of earth in proportion of their respective > mass, so the satellite causes earth to move around it's > theoretical orbit (if there was no satellite). The earth > movement is very small (could not be measured for an > artificial satellite, but but could certainly be calculated, > the effect of the moon on earth's orbit can certainly be > measured) but it causes an equal and opposite centrifugal > force on earth, which balances the force exerted on the satellite. > > So I believe there are 2 sets of forces (gravity and > centrifugal), and each set has a resultant that is null, as > seen from the outside. However, at the level of earth and the > satellite, the gravitational attraction is equal and opposite > to the centrifugal force. > > I did not know physics cared if we used inertial system > concepts or accelerated systems concepts (I do not know the > difference). > > If I follow your theory, the speed of the satellite around > the earth has no effect on gravity, so the satellite should > stay where it is regardless of speed, but it does not! > > Please explain this to me. > > I agree that as long as the distance between a satellite and > earth remains constant, the forces must balance each other. > But if it's not centrifugal force that is balancing gravity, > what is it? > > Thanks in advance > > Didier > > 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: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] 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 > > > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-> bin/mailman/listinfo/time-nuts > > > > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-> bin/mailman/listinfo/time-nuts > > > > > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-> bin/mailman/listinfo/time-nuts >
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