Why does the watch keep moving after leaving the bookshelf?

I = Σ miri2

and

γ=1√1−v2c2 γ = 1 1 − v 2 c 2

On the received view of Newton’s First Law of Motion, the law is exclusively concerned with the
motion of force-free bodies, stating that such bodies continue their state of rest or uniform motion in a
straight line. For instance, distinguished Newton scholar Brian Ellis formulates the law as follows:
“every body not subject to the action of forces continues in its state of rest or uniform motion in a
straight line” (Ellis 1965, 35). Richard Feynman’s lectures state it thus: “if an object is left alone, is not
disturbed, it continues to move with a constant velocity in a straight line if it was originally moving,
or it continues to stand still if it was just standing still” (Feynman et al. 1963, §6.2). Or take Thomas
Kuhn: “In the absence of an external force applied to it, a body moves continuously at constant speed
in a straight line” (2000, 68).
The thesis of this paper is that such paraphrases of Newton’s First Law are all incorrect, because the
law, as Newton stated it, is not just a description of the motion of force-free bodies. It is in fact a
stronger, more general principle, constraining the motion of all bodies. Here is Newton’s own
formulation of the law, in the authoritative Cohen and Whitman translation (Newton 1999, 416):
Every body perseveres in its state of being at rest or of moving uniformly straight forward,
except insofar as it is compelled to change its state by the forces impressed. (LI)
As I understand it, the phrase “except insofar” (nisi quatenus) does not exempt bodies that are subject
to impressed forces from the scope of the law altogether. Instead it puts a limit on the extent to which
the state of motion of any body can change: it changes only insofar as the impressed forces compel it to.
This principle rules out changes in speed or direction due to inuences besides impressed forces, like
loss of impetus, “natural motion” or spontaneous animation in living organisms.