• Work is a scalar.
  
  
• Only forces do work.
  
  
• Forces only do work when they move,
  
  
• and only when they move in the direction of their line of action.
  
  
• The work is POSITIVE if the displacement (motion) of the force is in the direction that it acts.
  
  
• The work is NEGATIVE if the displacement is in the opposite direction that the force acts.
  
  
• If the force and displacement are constant (both in magnitude and direction), then the work done is:
  
  Work = Force x Displacement
  where Force and Displacement are along the same line in space.
  
  
• If the force and displacement are not constant, then only a differential of the work can be calculated:
  
  d(Work) = Force x d(Displacement)
  
  
• This differential can be integrated over a finite displacement of the force to obtain the total work done by the force.
  
  
• The dot product of the force vector with the differential of the displacement vector is completely consistent with all of the above.