The kinetic friction force between two surfaces depends on the normal force and the coefficient of kinetic friction. When the angle of incline changes, it affects the normal force and, consequently, the kinetic friction.
The normal force is the force exerted by a surface perpendicular to the contact area. On an inclined plane, the normal force is not equal to the object's weight (mg), but rather the component of the weight perpendicular to the plane. The normal force can be calculated using the equation:
Normal force (N) = mg * cos(θ)
Where m is the mass of the object, g is the acceleration due to gravity (approximately 9.8 m/s²), and θ is the angle of incline.
The kinetic friction force (Fk) can be calculated using the equation:
Fk = μk * N
Where μk is the coefficient of kinetic friction between the two surfaces.
When the angle of incline changes, the normal force changes accordingly. If the angle increases, the component of the weight perpendicular to the plane increases, resulting in a larger normal force. Consequently, the kinetic friction force also increases because it is directly proportional to the normal force.
On the other hand, if the angle of incline decreases, the normal force decreases. As a result, the kinetic friction force decreases as well.
In summary, the kinetic friction force changes proportionally to the normal force, which is influenced by the angle of incline. If the angle increases, the kinetic friction force increases, and if the angle decreases, the kinetic friction force decreases.