Hello, I am almost surely doing something wrong here, but I think it would be better if I drew a diagram to illustrate what I mean. [PLAIN]http://img690.imageshack.us/img690/5830/workh.png [Broken] AB is Force, AC is displacement. Now I know that work here = Force . Displacement x Cos(theta), by constructing a perpendicular between AB and AC and using sine-cosine functions. When theta = 90, component of force along displacement equals 0 - this, I don't get, as since I use trigonometry to derive W = F . D x Cos (theta) I think I can do that here like this: [PLAIN]http://img193.imageshack.us/img193/2720/work2i.png [Broken] AC = Force, AB = Displacement. The angle formerly indicated as (theta) now has the sign of a right angle. Now here, tan(theta) = AB/AC or AC x tan(theta) = AB. Therefore F x tan(theta) = D. Thus Work = F.D.tan(theta). Where am I going wrong?