 Let us look at the thermodynamic definition of work. This is required because various branches of physics define the work interaction in different ways and we have to have a proper definition so that we accept some interaction as work interaction. The requirement for work to be considered as work interaction in thermodynamics are as follows. First one, the interaction must be an energy interaction and it should be between two systems. So two systems must be involved system A system B for a system and its surroundings. Second one is that this interaction must be completely reducible to the rays of a weight. By weight we mean some mass m in a gravitational field, this must be raised against the force of gravity. So the rays of a weight that is mass in a gravitational field, it is considered the basic idea of work and hence we consider that to be a work interaction provided that interaction is completely reducible to the rays of a weight. And for this complete reduction, there is a qualification, this should be by primitive means. That means means which are defined in other branches of physics. For example, we can use chains and pulleys, we can use pistons and cylinders, we can use gears, we can use block and tackle, we can use anything which is properly defined. Important thing to note is idealizations are acceptable. In the sense we can consider massless, inertia less, friction less pulleys. We can consider 100% efficient electrical generators and electrical motors. We can consider friction less movement. We can consider inflexible massless strings. All idealization is possible. However, black box approach, saying well I have something which will do it for me, that is not acceptable. Thank you.