# Why objects with magnetic dipole moment sometimes orient towards external B and other times they do precession?

Given the magnetic dipole moment in external uniform magnetic field $\vec{B}$, I am trying to understand why sometimes $\vec{\mu}$ simply aligns with the $\vec{B}$ and stays that way, while other times $\vec{\mu}$ starts precessing around $\vec{B}$?

I am interested in both the classical and the quantum concepts of this phenomenon. When I read quantum physics books it seems to me that in quantum world we always have precession and never simple alignment (interaction between say electron spin and external field):

while in classical world we sometimes get one and other times the other.

Is there some condition for precession? I am looking for an intuitive answer just to get some picture/concept in my head, not strict mathematical explanation.

• The dipole does indeed precise. In classical mechanics, we only approximate its allignment for simplification. This is only valid if the dipole turns quasistatically whrn B is switched on(hypothetical situation) – Lelouch Jul 5 '16 at 0:12