2) defines potential energy difference in terms
of the physically meaningful quantity work Clearly,
potential energy so defined is undetermined to within an
additive constant What this means is that the actual value
of potential energy is not physically significant; it is only
the difference of potential energy that is significant We can
always add an arbitrary constant a to potential energy at
every point, since this will not change the potential energy
difference:
(
)
(
)
P
R
P
R
U
U
U
U
α
α
+
−
+
=
−
Put it differently, there is a freedom in choosing the point
where potential energy is zero