why does heat flows from a high temperature body to a low temperature body? The above statement can be concluded from applying conservation of momentum to particles of a system containing a high and low temperature bodies. But in texts, its written that the above statement is a consequence of the 2nd law of thermodynamics. So is the 2nd law equivalent to momentum conservation principle? i mean, suppose we did not know the 2nd law, then could we explain the statement using momentum conservation and forget about entropy?