Temperature as measure of average KE of molecules

Question

This was asked to me in a Physics PhD interview. We suppose that a river is flowing, with its water in the middle flowing at much higher speed than that of the waters near the banks. If temperature is a measure of average KE of molecules, should the temperature of water in the middle be higher than those flowing near the banks, as the molecules in the former case have much higher velocity and consequently much higher KE?

My guess is that it shouldn't, but I'm unable to think of the reason for this. Also, I'm not sure whether my guess is the correct one or not. How should I approach this question?

Answer 1

Temperature is a measure of the average molecular kinetic energy associated with the random motion of the molecules, not the kinetic energy associated with the collective motion of the molecules, like those of the flowing river.

Would you expect the temperature of your cup of coffee to increase after getting into a moving car?

Hope this helps.

Answer 2

No, temperature is a measure of average kinetic energy in the frame where the liquid is at rest. Translational velocity of macroscopic elements of water is not related to their temperature in any way.