In physics, the normal force is the force that a surface exerts on an object in contact with it, perpendicular to the surface. It is often called the normal reaction or the contact force. The normal force is equal in magnitude to the perpendicular component of the force exerted by the object on the surface, and it acts in the opposite direction.

For example, if an object is resting on a horizontal surface, the normal force is equal in magnitude to the weight of the object and it acts vertically upwards. If the object is pushed down on the surface, the normal force increases in order to counteract the increased force exerted by the object on the surface.

The normal force is always perpendicular to the surface, regardless of the angle at which the object is in contact with the surface. This is because the normal force is a reaction to the force exerted by the object on the surface, and the reaction force is always equal and opposite to the action force.

The normal force is an important concept in physics, as it is used in many calculations involving objects in contact with surfaces. For example, the normal force is used to calculate the coefficient of static friction, which is a measure of the resistance of an object to sliding on a surface.