An inclined plane, is an even surface that is tilted at an angle. It helps reduce the force necessary to move an object by increasing the distance it must be moved. The inclined plane consists of a smooth plane hinged to a base so that it can be set at any desired angle. If a body of mass (say m) is placed over an inclined plane, that is inclined at an angle θ with the horizontal, its weight mg acts vertically downward. The component mg cosθ of the weight acts normally downward on the plane balances the upward normal reaction (say R) of the inclined plane. The component mg sinθ of the weight acting parallel to the inclined plane downwards, produces motion in the body.
This video explains how to (a) find the downward force along an inclined plane, acting on a roller due to the gravitational pull of the earth and (b) study its relationship with the angle of inclination θ by plotting a graph between applied force and sin θ.