Technically a massive or a charged object moving in a circular path should emit radiation, gravitational or electromagnetic.
The gravitational radiation emitted by a planet is extremely small so the energy loss is not going to affect the orbit dynamic even over enormous period of times. In certain systems where the gravity involved is much higher (very close neutron stars binary systems) though the energy loss would make the orbit radius smaller and smaller with time (until the objects actually collide). A classical electron should emit a lot of radiation orbiting a so high velocity around the nucleus of an atom and should collapse into the nucleus in a very short time. This doesn't happen and it puzzled the scientists of the early 20th century. Eventually quantization of the electron orbits was used as a way to solve the problem, but it is a unsatisfactory solution because basically it makes an axiom what is not explained (that certain orbits are allowed around he atom and they are stable per se). I never heard a very good explanation of why this should be true, even thinking about the electron as a distributed charge over the entire orbit is not really a very good explanation. It is an unresolved problem in modern physics. But yes in classical physical at first approximation a neutral object moving in a circle in a central gravitational field does no work because is moving perpendicular to the force at any moment. Giovanni On Mon, Sep 3, 2012 at 8:28 PM, Harry Veeder <hveeder...@gmail.com> wrote: > On Mon, Sep 3, 2012 at 7:48 PM, Jouni Valkonen <jounivalko...@gmail.com> > wrote: > > > However I do not think that it is anymore complex idea than refrigerator > magnet that is doing endless work >against gravity or electron that can > orbit nucleus without losing it's energy. > > In your example no work is performed according to the definition of > work that physicists developed about two centuries ago. Unless the > magnet displaces itself upwards the magnet hasn't accomplished > anything from the standpoint of conventional physics. Unfortunately > physics has no concept of stationary work. > harry > >
