In a simple case such as an object resting upon a table, the normal force on the object is equal but in opposite direction to the gravitational force applied on the object (or the weight of the object), that is, , where m is mass, and g is the gravitational field strength (about 9.81 m/s2 on Earth).
What is normal force and what causes it?
The most common normal force is caused by gravity, as seen in the man on the platform. 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.