How is the normal force defined on a contact surface?

How is the normal force defined on a contact surface?

• A. The frictional force parallel to the surface.
• B. The component of the contact force perpendicular to the surface.
• C. The weight of the object.
• D. The net force on the object.

Answer: (B)

The normal force is the force from a surface on an object that prevents it from passing through the surface, and it acts perpendicular to that surface. It arises from the constraint of contact, so the surface pushes back in a direction normal to the contact plane. The normal force is therefore the component of the contact force that points perpendicular to the surface. It’s not the friction, which acts parallel to the surface, and it isn’t the weight, which points downward due to gravity. It also isn’t the net force, which combines all forces and can have both perpendicular and parallel components to the surface. In simple cases on a horizontal surface with no other vertical forces, the normal force balances the perpendicular components of gravity and any other perpendicular loads, but in general it adjusts to match those perpendicular forces to prevent penetration.

The normal force is the force from a surface on an object that prevents it from passing through the surface, and it acts perpendicular to that surface. It arises from the constraint of contact, so the surface pushes back in a direction normal to the contact plane. The normal force is therefore the component of the contact force that points perpendicular to the surface. It’s not the friction, which acts parallel to the surface, and it isn’t the weight, which points downward due to gravity. It also isn’t the net force, which combines all forces and can have both perpendicular and parallel components to the surface. In simple cases on a horizontal surface with no other vertical forces, the normal force balances the perpendicular components of gravity and any other perpendicular loads, but in general it adjusts to match those perpendicular forces to prevent penetration.