When a Force Is Called a "Normal" Force, It Is

Multiple Choice

When a force is called a "normal" force, it is

A) the usual force expected given the arrangement of a system.
B) a force that is perpendicular to the surface of the Earth at any given location.
C) a force that is always vertical.
D) a contact force perpendicular to the contact surfaces between two objects.
E) the net force acting on a system.