Work is energy being used.
When you slide a box across a floor, you use your energy to do this work.

Work = force * distance = joules

Picture this:

  • You lift a box up 1m above the floor (you do work and the box gains PE).
  • If you drop the box, it gains energy and wham, it hits the floor.
  • If you carry the box across the room and drop it there, it still falls from only one meter up, so has gained NO energy by being carried across the room.


    • THIS MEANS that technically, you did no work in carrying the box across the room; you only did work in lifting it against gravity.

    In fact, when the motion is perpendicular to the force, work is not done.
     
     

    Another example:

  • You pull a box by a string across a floor.
  • If you pull horizontal to the floor, all of your pulling goes into the box's motion.
  • If you pull so that the rope tilts upward somewhat, your sideways force is diminished and goes into lifting the box upward.
  • Once the angle of the rope with the ground becomes 90°, there is no motion along the floor.


    • The more specific equation for work then becomes W = F*x*cosq