# Free Electron Theory of metals

I don't quite get the concept of drift velocity. According to definitions, it is the net velocity with which the electrons are drifted in a direction opposite to the applied electric field. Is the thermal velocity included in that or is it different? According to what I have read drift velocity goes to zero after each collision but thermal velocity still remains right? And how does it differ from the root mean square velocity of the electrons? Can someone please explain this to me ?

You can consider the mobile electrons as having random thermal motion (speeds of the order $$10^5 \rm m\,s^{-1}$$) with a mean drift velocity due to the application of an electric field (speeds of the order of fractions of $$\rm mm\,s^{-1}$$) superimposed on the random thermal motion.