La fuerza normal: ？una fuerza conservativa?

the normal force is a constraint force that arises from the contact between an object and a surface. this force can preserve the mechanical energy of a system or not. it is shown that normal force is conservative when the surface does not evolve over time, as well as the rate to which the mechanical energy changes when the normal force is not conservative. for the latter situation, it is proposed the pseudo-potential energy function associated to normal force in order to obtain from energetic considerations the equation of movement of the object under the above mentioned force.