A little consideration will show that if the inclination of the plane, with the horizontal, is less than the angle of friction, the body will be automatically in equilibrium. If in this condition, the body is required to be moved upwards or downwards, a corresponding force is required for the same. But if the inclination of the plane is more than the angle of friction, the body will move down. An upward force (P) will be required to resist the body from moving down the plane as shown below figure:
Though there are many types of forces, for the movement of the body, the following are important from the subject’s point of view:
1. Force acting along the inclined plane.
2. Force acting horizontally.
3. Force acting at some angle with the inclined plane.