 Let's take an electric dipole, for example a molecule with a positive and negative charge. If we place it in a homogeneous electric field E of a plate capacitor, then the negative charge experiences a force F1 towards the positively charged plate. The positive charge experiences a force F2 toward the negatively charged plate along the electric field. The dipole rotates until it is parallel to the electric field lines, such that the negative charge is on the side with the positive plate and the positive charge is on the side with the negative plate. The resulting force on the electric dipole is then also zero in this state. In a homogeneous field, the electric dipole rotates but does not move. Let us now generate an inhomogeneous electric field with a charged sphere. In this inhomogeneous field, the electric dipole will rotate until it is aligned along the field lines. But something else happens in the inhomogeneous electric field besides rotation. The positive and negative charge of the electric dipole experience a different force along and against the field lines. To bring the two forces into equilibrium, the dipole shifts in the inhomogeneous electric field.