Deriving force from inductance

The correctness of calculating the force on current carrying circuits by taking the derivative of the inductance coefficient of the circuits is shown even in the case of a single closed circuit, contrary to the opinion of some authors. This demonstration is illustrated with the force exerted by a cylinder with poloidal current on an infinitesimal strip belonging to the same cylinder. The force is calculated directly from the force expressions and also by differentiating the self-inductance of the cylinder. This result is another proof of the equivalence between Ampere and Grassmann´s forces