What is the primary factor affecting the frictional force on an inclined plane?

The primary factor affecting the frictional force on an inclined plane is indeed the coefficient of friction and the normal force.

Frictional force is fundamentally described by the equation ( f = \mu N ), where ( f ) is the frictional force, ( \mu ) represents the coefficient of friction (which depends on the materials in contact), and ( N ) is the normal force acting on the object due to gravity.

On an inclined plane, the normal force is less than the weight of the object because it is affected by the angle of the incline. As the angle increases, the normal force decreases, which in turn influences the frictional force acting against the motion of the object. Therefore, both the coefficient of friction (reflecting the material properties) and the normal force (due to the incline) are critical for determining the total frictional force experienced by the object on the slope.

This relationship illustrates why simply considering the weight of the object, the angle of the incline, or the type of material alone, without acknowledging both the coefficient of friction and the normal force, is insufficient to fully understand friction on an inclined plane.