the normal force is a Perpendicular Force to any surface (surface being a plane) of contact, of the contact force exerted on an object by, for example, the surface of a floor or wall,the normal force prevents the object from penetrating the surface.

Of all physical forces in everyday life, perhaps the most common is the normal force. The normal force comes into play any time two bodies are in direct contact with one another, and always acts perpendicular to the body that applies the force. The simplest example of the normal force can be seen in the situation of a man standing on a platform. Clearly a gravitational force acts on the man, pulling him down, perpendicular to the platform; but since the man is not moving, another force must act to counteract the gravitational force. This force is applied by the platform, and is called the normal force, and is referred to as F _N .

Since the normal force is a reactive force, its magnitude is independent of the nature of the force causing it. The most common normal force is caused by gravity, as seen in the man on the platform. However, there can be additional forces that also cause a normal force.

Consider a block on a platform with weight 10 N. In addition, someone pushes downward on the block with an additional force of 15 N. The platform thus experiences a total force of 25 N, and reacts with a normal force of 25 N, keeping the block in equilibrium. Thus, in the situation of a horizontal object, the normal force is simple: it is merely equal in magnitude and opposite in direction to all forces applied to the surface.