Normal force

Normal force is the force that the ground (or any surface) pushes back up with; If there was no normal force, you would slowly seep into the ground.
The normal force on a object is always perpendicular (at a right angle) to the surface the object is on.
On a flat surface, the normal force of an object is formula_1 (the object's weight, that is its mass multiplied by the force of gravity).
On an inclined plane, the normal force is reduced by the angle, and the normal force is formula_2.
Note that on a flat surface, formula_3 (angle)would be 0, and so formula_4 would be 1. Thus, the two equations are equal.