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.
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