Normal force

When some body rests on a surface, the contact force the surface puts on the object may always be shown as components of force parallel and perpendicular to the surface upon which the object rests. It is the perpendicular component of the contact force that we commonly call the "normal force". The other, parallel force, is known as the frictional force. In a simple case such as a $40kg$ object resting upon a table, the normal force from the table to the object is equal but in opposite direction to the force applied to the table by the object in this case, $40kg*9.81m/s^{2}=392.4$ Newtons where $9.81m/s^{2}$ is equal to the force of gravity.