Work done by friction on a body? I know that when a body slides over a surface, the work done by friction is not stored as potential energy in the body. It is dissipated in the form of heat.
But why is it not stored as potential energy? I know that there is something related to conservative and non conservative force but I don't get it.
 A: The general statement of the conservation of the energy is
$$
W_{\textrm{non-cons}}= (T_{\textrm{init}} - T_{\textrm{fin}})_{\gamma}
$$
hence the work done by any non conservative force (in this case the friction) is equal to the difference in kinetic energies along the path $\gamma$. Friction is a non-conservative force, that is, by definition, there is no function such that it is the gradient thereof; as a consequence its work explicitly depends on the path you follow and cannot be computed as the mere difference of a potential function in two any points. This is basically the reason why it is not stored as potential energy: being a non-conservative field implies there is no potential energy associated (it cannot be defined).
Friction is essentially the macroscopic name that people use to refer to the electromagnetic interactions among the components of the bodies in contact. It is stored in the form of heat because it generates electromagnetic waves (oscillations of the atoms in the material) that we macroscopically detect as heat due to absorption and emission of photons during the process.
