In All the Classical Mechanics problems I have come across so far, There's one thing that happens invariably: That the work done by tension is zero. Mostly, It simply happens because the (massless) string is in-extensible(And therefore, no displacement),And the tension in the string is the same.
- A pulley with mass, that is free to rotate, has a string(with blocks connected at its free end) wrapped around it.When the system is released, The tension in the Two pieces of string will be different, yet the displacement of the blocks along the string will be equal and opposite. Why is work done by tension zero here? It seems to me that the work done should be $T1*x + (-T2*x)$
- A fixed disc free to rotate about its center (a flywheel)has a string wrapped around it, with a block attached to it. As the block falls, The tension in the string makes the disc rotate. Now, When the disc rotates by an angle $\theta$,(assuming the string doesn't slip) a length=$r\theta$ of string unwraps. The length of the piece of string which is attached to the block is changing. Why is work done by tension zero?(on block +disc system)
- How can we, (if it is true,that is), generalize that the work done by tension is always zer0? An earlier explanation that I had was that its an internal force.However, I believe internal forces can do work: for example, a spring connected to two blocks does work. An explanation given to me by a friend , was : "A mass-less string cant store energy", which seemed reasonable at first, But i believe the concept of "storing energy" requires the concept of work itself, which makes this argument circular.