The normal force is a contact force that acts perpendicular to the surface of an object. It occurs when an object is resting on a surface, such as a book on a table. This force balances the weight of the object, preventing it from falling through the surface. For example, when a person stands on the ground, the ground exerts an upward normal force equal to the person's weight. This interaction is crucial in understanding how objects remain stable and how forces are balanced in everyday situations, such as when a car is parked on a slope or a box is placed on a floor.