If velocity is subjective to an observers frame of reference?

[zeromodz]

If velocity is subjective to an observers frame of reference, then isn't energy (kinetic) also subjective? How can we define energy as objective if it changes depending on your frame of reference?

 

[Dale]

If velocity is subjective to an observers frame of reference, then isn't energy (kinetic) also subjective? How can we define energy as objective if it changes depending on your frame of reference?

The usual terms are "frame variant" instead of "subjective" and "invariant" instead of "objective". Energy is frame variant, this is not due to relativity, it is frame variant in Newtonian physics also.

 

[Acut]

We don't define energy precisely, since what really matters for our equations is the difference of energy between to instants of time.

We can't find a priviledged frame of reference - a fact known since Galileo and latter confirmed again and again with Einstein's ideas.