# Breakdown of Ehrenfest theorem for free particle constrained on a hypersurface. (arXiv:1802.01849v1 [quant-ph])

There is a belief that the Ehrenfest theorem holds true universally. We
demonstrate that for a classically nonrelativistic particle constrained on an
$N-1$ ($N\geq 2$) curved hypersurface embedded in $N$ flat space, the theorem
breaks down.