Because of the static friction, the cargo and the conveyor belt remain relatively stationary (this static state refers to the trend of movement).
The criticality is still), so when the conveyor moves, the goods move accordingly. It is because of the static friction that the goods are not lost.
Down, you will ask because you reversed the direction of static friction.
Sliding friction is the force that hinders the advancement of the object, and the force is generated at the point of action (contact or contact point), and because of the cargo and
There is only one contact surface for the desktop, etc., that is, the contact surface between the belt and the cargo, so it is positive with the force generated at this contact surface.
Compared to this, and this force is only pressure