Originally Posted by ShoeDLG
The term "work" has a very specific meaning in Physics. The work done on a body is the force applied to a body times the displacement of the body in the direction of the applied force. It follows directly from this definition, that motion of the body perpendicular to an applied force will result in no work done by that force. You don't need to be technically sophisticated to grasp that.
And there's a very good reason for this definition. Forces perpendicular to the motion of the body do not alter the energy state of the body. Thus, they do no work. If this were not true, you could say goodbye to the study of dynamics and many other fields.