The energy of confinement is a purely quantum effect. In classical
physics the particle may sit at rest with zero kinetic energy. It is
the Heisenberg Uncertainty Principle which forces the spread in
momentum giving rise to the non-zero kinetic energy. As this effect
is not seen in classical physics, we must conclude from the
correspondence principle that the effect is tiny in a macroscopic
situation. For instance, for a ball on a pool table (
,
), we find 
, a truly
negligible effect. There is a
more formal way to look at this that does not require inserting the
tiny value of
into the expression and running the numbers. One may instead take the mathematical
limit 
to find
that the effect ``vanishes'' in ``the classical limit''. In a sense,
controls the importance of
quantum mechanics and taking the limit 
is a
way of ``turing off'' quantum mechanics.