Normal force

File:Incline.gif

F_n represents the normal force.

In physics, the normal force (F_N) is the perpendicular component of the contact force exerted by, for example, the surface of a floor or wall, on an object, preventing the object from entering the floor or wall. In a static situation it is just enough to balance the force with which the object pushes, e.g. its weight on the floor, or a smaller force if somebody leans against a wall. If an object hits the surface with some speed, the normal force provides for a rapid deceleration, depending on how flexible the floor/wall is (and, of course, if it can provide enough force instead of breaking). Also, if the object is soft, only the outer part needs to decelerate rapidly, the inner part can do that more gradually, while the layer in between is compressed.

Note that the sign of the calculated value will be either positive or negative depending upon whether the positive Y-axis is taken to be either positive or negative.

Frictional force

The parallel component of the contact force is known as the frictional force (F_f).

Example

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 (i.e. weight of the object). In this case the normal force is given by, $40kg*9.81m/s^{2}=392.4$ newtons where $9.81m/s^{2}$ is equal to the acceleration due to gravity (near the Earth's surface).

Real world applications

In an upwardly accelerating elevator, the normal force does not only balance the weight, but also provides upward acceleration to the person standing in the elevator, preventing him/her from staying behind and passing through the floor of the elevator.