Fn is the normal force between the load and the plane, directed normal to the surface, and μ is the coefficient of static friction between the two surfaces, which varies with the material. When no input force is applied, if the inclination angle θ of the plane is less than some maximum value φ the component of gravitational force parallel to the plane will be too small to overcome friction, and the load will remain motionless. This angle is called the angle of repose and depends on the composition of the surfaces, but is independent of the load weight. It is shown below that the tangent of the angle of repose φ is equal to μ With friction, there is always some range of input force Fi for which the load is stationary, neither sliding up or down the plane, whereas with a frictionless inclined plane there is only one particular value of input force for which the load is stationary. Analysis A load resting on an inclined plane, when considered as a free body has three forces acting on it: The applied force, Fi exerted on the load to move it, which acts parallel to the inclined plane. The weight of the load, Fw, which acts vertically downwards The force of the plane on the load. This can be resolved into two components: The normal force Fn of the inclined plane on the load, supporting it. This is directed perpendicular (normal) to the surface. The frictional force, Ff of the plane on the load acts parallel to the surface, and is always in a direction opposite to the motion of the object. It is equal to the normal force multiplied by the coefficient of static friction μ between the two surfaces. Using Newton's second law of motion the load will be stationary or in steady motion if the sum of the forces on it is zero. Since the direction of the frictional force is opposite for the case of uphill and downhill motion, these two cases must be considered separately: Uphill motion: The total force on the load is toward the uphill side, so the frictional force is directed down the plane, opposing the input force. The mechanical advantage is where . This is the condition for impending motion up the inclined plane. If the applied force Fi is greater than given by this equation, the load will move