$W = Fd$, meaning if a body moved a distance, say $3 m$, and returns, its distance will be zero and work will be zero. I do understand it mathematically and graphically but can someone explain it to me practically, specifically how that person does $0$ work. Also, when is work negative Also concerning gases , if they are compressed work will be with negative value is there any relation?!
P.S. I am a student so pardon my ignorance.
You do work to move it the first 3 meters. You do the same amount of work to move back the same 3 meters, but this time the work has opposite sign. In total, no net work is done.
When only conservative forces are acting then this is the case and only the start and end position matters, not the path.
If non-conservative forces like friction were acting, then you would also have to do work to overcome friction in both directions and the net work would be non-zero.
Think about it in terms of natural movement, where energy is conserved. A good example where zero net work is achieved, but symmetrical movement is observed is of course the good old pendulum.
Your pendulum (starting off equilibrium of course) experiences a gravitational force pulling it down, but whose work is compensated as soon as the pendulum goes back up again on the other side. Same goes for the tension along the string.
