I know the definition of the electric dipole moment is given by [tex]\mu = -e x[/tex], where e is the charge of electron and x is the displacement. I am thinking a mechanics counterpart of the dipole moment. We note that in mechanics, the moment is defined as the force cross the position vector. Consider 1D problem, the force of electric field is given by [tex]F = -e E[/tex] where E is the electric field. So the moment should be [tex]\mu = Fx = -eE x[/tex] but why this is different from the one in text ([tex]\mu=-ex[/tex]) ? What's wrong in my reasoning?