Dear All, Suppose there is a a pulley with mass and a massless cord around it, if pulley is rotating then I have learned that there are different tensions on either side of the pulley. I am having some trouble visualizing it. Moreover, if there are two different tensions on the cords, where exactly they are separated from each other ? I have searched a little bit and read that thread several times : https://www.physicsforums.com/showthread.php?p=1958707 There is a statement on that thread which is; Could you please explain this further ? Why and how it can have different tension on either side, if a string is touching somewhere and where these tensions are seperated ?