Molecular dynamics simulations of the sliding friction between two thick solid slabs are performed. The upper body is formed of light N(2) particles and the substrate of heavy Pb atoms. Among the various mechanisms that are responsible for the friction, we consider the phonon-phonon interaction between the two blocks. To provide evidence of the phonon interaction, we compare two different systems. For the first we consider the substrate as formed of atoms fixed in the equilibrium (111) positions. In the second system the Pb atoms can be displaced from the ideal positions, under their mutual interactions. A comparison with recently obtained experimental data will be discussed.