[time-nuts] FW: Pendulums & Atomic Clocks & Gravity

[Didier Juges]

James,

Where were you all week-end?

Your explanations are so clear, it makes sense now. Thank you very much.

I understand now that centrifugal forces are necessary to explain the behavior of objects when an accelerating frame of reference is used, but not necessary (actually counter-productive) to explain the behavior of the same objects when an inertial frame of reference is used.

That solves my problem and the apparent contradiction that sometimes the centrifugal force is necessary and sometimes not, because I did not appreciate the effects of changing the frame of reference.

Thanks a lot again.

I had no idea time-nuts would drive me to brush-up on physics :-)

Didier KO4BB

---- James Maynard <james.h.maynard at usa.net> wrote: 

> The reason that the frame of reference matters is that gravity is 
> indistinguishable from acceleration. (This is an assumption that 
> Einstein made when deriving his general theory of relativity. It seems 
> to work.)
> 
> An "inertial" frame of reference is a non-accelerating frame of 
> reference. In an inertial frame of reference, Newton's laws of motion 
> work -- if you use Newton's gravitational relationship, that the 
> gravitational force (weight) that each of two bodies exerts on the other 
> is proportional to both their masses, and inversely proportional to the 
> square of the distance between them.
> 
> In an accelerating frame of reference (either linear acceleration, or 
> rotational acceleration, or both) additional forces, technically called 
> "fictitious" forces, must be introduced in order to explain the motions 
> of bodies with Newtonian mechanics. The "fictitious" forces on a body 
> are also proportional to the body's mass. (A body's mass is just a 
> measure of its inertia: to accelerate at an acceleration "a", a force 
> "F" must be applied, and the mass "m" is just F/a.)
......