I am just discussing gases and how substances change when they undergo temperature changes. We know that temperature is a measure of the average speed of a substance. Okay, but when we look at velocity, it has both direction and a magnitude. So, when we heat a substance (ex. water), I understand that its molecules' average speed increases, but does its net velocity? Since all the molecules are pointing in random directions, wouldn't there be a net cancelling effect on the velocities of the individual molecules in this sample since it is a vector quantity we're assessing? For a cup of quiescent water, there is no net velocity, right? So if we were to either cool or heat this sample, it still wouldn't have a net velocity change, right? Any clarification on the above matters would be great since I'm having trouble finding discussions regarding velocity changes instead of just speed changes. Thank you!