Thermal energy is momentum right? Is this a correct interpretation: If I slide an object across a frictional surface, the momentum will still be conserved, just not visibly (because it's now atomic momentum, called "thermal energy"). If yes, then, in all of these conservation of momentum problems I'm doing, why is it safe to assume that some of the momentum is not converted into thermal energy? If two objects collide, surely you would expect an increase in thermal energy? Is it just that even large amounts of thermal energy have negligable momentum? Or is there another reason? Is thermal energy even momentum?