Originally Posted by **lancew561** You believe it really begins (down) with the source of the acceleration in comparison to the local forces like gravity. If multiple gravity or other fields interact it would also become undefinable lacking true reference frame and again remain undefinable also?
This means the definition is undefined as the definition?
And yes I do believe definition is most important frankly seeing science for years using many terms which are really not well defined to old or modern physics.
Hard to truly solve any equation without knowing exactly what the variables truly are is it not? |

As it happens there are two (at least) views about this. The first is that defining a coordinate system for a process is good because it gives a way to analytically break down the Mathematics of the process. The second is that many Mathematical developments in Physics come from almost entirely throwing away the concept of a coordinate system which allows us to proceed in a more theoretical way.

Putting the two together gives the concept that it does not matter which coordinate system we pick... we just have to stick to one once we've defined it.

-Dan