The normal force is the force exerted by a surface to support the weight of an object resting on it. On a flat surface, the normal force is equal to the weight of the object. However, when the surface is inclined, the situation changes.
When an object is placed on an incline, the weight of the object acts straight down towards the center of the Earth. This weight can be broken down into two components: one that acts perpendicular to the incline (the normal component) and one that acts parallel to the incline (the gravitational component that causes the object to slide down).
Since the incline supports the object only against the component of the weight that acts perpendicular to its surface, the normal force will be less than the total weight of the object. Mathematically, we can express the normal force (N) as:
N = W * cos(θ)
Where W is the weight of the object and θ is the angle of the incline. As the angle increases, the cosine of that angle decreases, which results in a smaller normal force. Therefore, on an incline, because part of the gravitational force is directed down the slope, the normal force cannot equal the weight, and it becomes less than the object’s weight.