Consider a book that remains at rest on an incline. Draw a free-body diagram that shows the directions of the forces acting on the book Are they opposite in direction?
a) No; the normal force acts perpendicular to the surface of the inclined plane.
b) No; the normal force acts up the incline to keep the book from sliding down.
c) Yes; the normal force always acts opposite the weight force. Otherwise, the book would fall through the inclined plane.
d) Yes; the normal force acts opposite to the weight force because the book is stationary.