THE NORMAL FORCE

       When an object is in contact with a surface, the surface exerts a content force on the object. the component of the contact force that's perpendicular  to the surface is called the normal force on the object. (In physics, the word normal means perpendicular.) The normal force is what prevents objects from falling through tabletops or you from falling through the floor. The normal force is denoted by F or simply by N. ( If you use the letter notation, be careful not to confuse it with N, the abbreviation for the newton.)