I just thought of work & energy as follows work A force F when moves through a distance x we say that work is done. In this we say that the component of force acting along the direction of displacement does the work. Why we say that? What the other component does? potential energy we say that potential energy of a system is its potential to do work. When we apply a force to a mass and the mass moves thro a distance x the the stored potential energy is F x X so i say that the mass has the potential to do a work of F x X. I imagine a situation where a box on a table is moved by a distance X horizontally. The box is not having any potential energy to do work. Why is this?