I am having few doubts regarding pulley,strings and tensions . The doubts are 1)Can a massless pulley rotate ? My reasoning - Yes .Just like a massless string can accelerate with zero net force .The same way a massless pulley can rotate with zero net torque. 2)Is tension in a massless string always same when it moves over a pulley .The string may be slipping(not sufficient friction) ,not slipping(sufficient friction,so moving along with the rotating pulley). 3)If the pulley is massless and the string is not massless,what are the tensions on the two sides? My thoughts-Since the pulley is massless,the tensions at the end points of segment of string over the pulley should be same.But the tension in a string having mass is not same at any two points . 4)How does friction between string and the pulley affect the tension on the two sides of the string? Kindly help me in clearing the concepts.