[camacazio]

Yeah supa and that's an important thing to keep in mind in any physics. If the values are negligable, it's best to ignore them (the transfer of mass from atoms during friction is almost nothing). That is why so many equations lasted so long without going into question. Newtonian mechanics are perfect for the world on our scale. Quantum mechanics and relativistic physics were fields of science that began discovering ways in which the old newtonian mechanics were flawed under deep scrutinization--the super fast and the super small. Frictional force as it is has not been researched much. At the quantum level, one would have to factor in ideas including some such as sethomas has brought up, but it's not an issue of math. It's an issue of research. Or statistical mechanics, but I've had only a little class time on that field outside of the kinetic theory of gasses. As far as my equation goes, I'd have to assume that the surface doesn't get entirely melted by the energy transfer of the rocket ship.