Proper noun
the Ehrenfest theorem
(physics) A theorem that relates the time derivative of the expectation values of the position and momentum operators x and p to the expectation value of the force
F
=
−
V
′
(
x
)
{\displaystyle F=-V'(x)}
on a massive particle moving in a scalar potential
V
(
x
)
{\displaystyle V(x)}
.
Classical quantities appear in quantum mechanics in the form of expected values of observables, and as such the Ehrenfest theorem (which predicts the time evolution of the expected values) lends support to the correspondence principle. Source: Internet