Juanita studies several free-body diagrams in which a normal force is shown. What is always true about a normal force in a free-body diagram?

A normal force is the contact force a surface exerts on an object. By definition, it acts perpendicular to the surface at the point of contact, so the correct choice is “It is perpendicular to a surface.” It is not always opposite the weight; that is true only in certain situations, such as an object resting on a level floor.

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