# If velocity is subjective to an observers frame of reference?

1. May 19, 2010

### 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?

Last edited: May 19, 2010
2. May 19, 2010

### Staff: Mentor

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.

3. May 19, 2010

### 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.