Suppose I am sitting on a bench and looking at a moving car. Force is applied on the car by its engine, and it makes it displace, hence some work is done on the car. But what if I am sitting in the car and looking at the bench? The bench covers some displacement, but who has applied force to it? Is any work done on it?
[Physics] Does work done depend on the frame of reference
newtonian-mechanicsreference frameswork
Best Answer
It's a good question. You're right that the bench has kinetic energy in the car-frame, so it seems natural that somebody had to do work on it.
That's not true, however. The energy of an object can be completely different depending on what reference frame you look at it from. So can the work. But in this case, the work on the bench is 0 no matter how you look at it, because the force is zero. So even if there is a displacement, $$W=0\cdot d=0.$$
In an inertial frame (one not accelerating), you only require work to change the energy of an object. In the car's frame, the bench has some kinetic energy, but it always had that kinetic energy. So nobody had to apply work to it.