Q: force on a piece of magnetized material Suppose that we have a magnetized piece of material that we put into a non-uniform external magnetic fiel $\vec{B_e}$, which is stationary. Is it true that the force on this piece a material is :

$\vec{F}=(\vec{M}\cdot \vec{\text{grad}})\vec{B_e}$

where $\vec{M}$ is the magnetization vector.
