Original Post
This video explains that "Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it." applies to a thrown rock that falls back on Earth too, not only for straight line inertial movements, AAAAAAAAND... that the rock travels just as fast (c) through spacetime as an individual photon, at all times when there are no interactions with other rocks (and molecules in the air.)