The normal force is a contact force that acts perpendicular to the surface of an object. It occurs when an object is resting on or in contact with another surface, such as a table or the ground. This force helps support the weight of the object and prevents it from falling through the surface. For example, when a book is placed on a desk, the desk exerts an upward normal force equal to the weight of the book. If the forces are balanced, the book remains at rest. The normal force can change depending on the angle of the surface or additional forces acting on the object.