A
concept that states that all events can be
modeled from within independant
inertial
frames of reference and still yield the same result.
IE: a ball thrown from
point A to
point B strikes B. When obsereved by a moving
vertex C may have a different
velocity when observed from A but the net
force on B is observed as the same from either A or C.
In really small words:
It don't
hurt you more if
I run after
he throws.