When a ball moves perpedicular about sloped direction, what should we concern between kinetic friction and static friction? When a plane has a slope due to the x-axis, and a ball has an initial $V$ along the $y$-axis. It is natural that we should concern kinetic friction along the $y$-axis.
But I am confused with should I concern what kind of friction along the $x$-axis.
If we adopt 'independence', we can consider the ball's movement as a stationary situation along the $x$-axis. So, I should concern static friction. But in my imagining, when a ball moves along the $y$-axis, I predict the ball would drop along the $x$-axis as well.
What should I concern about it between kinetic friction and static friction?
 A: If a ball is rolling down a slope, there will be a static friction force acting on the bottom of the ball and directed up the slope.
A: If the ball is rolling across the plane, rather than sliding, then the point on the ball that is in contact with the plane at any one time is stationary with respect to the plane. So you need to consider static friction, not kinetic friction.
There are three forces acting on the ball - its weight, the normal force from the plane, and friction. The normal force must equal the component of the ball's weight perpendicular to the plane. And if you know the normal force and the coefficient of friction, then you can find the magnitude of the frictional force.
The direction of the frictional force is more difficult. It will be in the opposite direction to the direction of ball's motion across the plane. But the direction of the ball's motion is constantly changing. The $y$ component of the ball's velocity is being reduced by the $y$ component of friction. The $x$ component of the ball's velocity is being decreased by the $x$ component of friction but increased by the component of the ball's weight in the $x$ direction. You will also have to consider the rotational dynamics of the ball, for which you need to know its moment of inertia.
A: There is no motion of the ball along the surface of the inclined plane relative to the inclined plane so the friction is static and is self adjustable to prevent sliding along the surface
