Are momentum and inertia definite ?

[synch]

If an object is moving it has momentum .. but if the frame of reference is altered so the speed matches, the momentum apparently vanishes (?!). Likewise with apparent inertia during acceleration of an object - similar acceleration of the frame can radically alter the perceived affect. Can absolute measurements be made in Newtonian physics?

 

[Dale]

if the frame of reference is altered so the speed matches, the momentum apparently vanishes (?!).

Yes.

Likewise with apparent inertia during acceleration of an object - similar acceleration of the frame can radically alter the perceived affect.

I don’t understand this comment.

Can absolute measurements be made in Newtonian physics?

In Newtonian physics some concepts are relative to the chosen reference frame and other concepts are invariant under a choice of reference frame. Velocity, energy, momentum, etc, all depend on the reference frame. Mass, distance, duration, etc., do not.

This general categorization also holds in relativity, but the specific list of relative vs invariant quantities differs. For example momentum is relative in both and mass is invariant in both, but duration is invariant in Newtonian mechanics and relative in relativity.