Gravitational, normal, and parallel forces
Every slope is at an angle to the ground, and an object placed on that slope will have the force of gravity acting on it. That force is broken down into the normal force, which holds the object onto the slope, and the parallel force, which causes the object to move down the slope.
Move points D and E. Notice that angles α and β remain the same. Observe how changing the angle affects the forces. If you know anything about the unit circle, adjust point D so that gravity=1 and then move point E and see how the values relate to the unit circle.