To analyze the frictional force of an object on a conveyor belt, the following three questions need to be clarified first:
1. Selection of reference objects for objects on the conveyor belt
The friction force of objects on the conveyor belt should be based on the conveyor belt in contact with the object, not on the ground or objects that stop relative to the ground.
2. Method for determining the direction of frictional force on an object on a conveyor belt
The key to determining the direction of friction of an object on a conveyor belt is to distinguish whether the object is sliding relative to the conveyor belt or has a relative motion trend. If it is relative motion, the direction of the sliding friction force experienced by the object is opposite to the direction in which the object slides relative to the conveyor belt; If there is a relative motion trend, the assumption method is usually used to first determine the direction of the object's motion trend relative to the conveyor belt, and finally determine the direction of the object's static friction force based on the opposite direction of the static friction force and the relative motion trend direction.
The method for determining the relative motion trend of an object on a conveyor belt is to assume that the contact surface between the object and the conveyor belt suddenly becomes lubricated. Under this condition, the analysis begins. If the speed of the object and the conveyor belt is still the same, it is explained that there is no relative motion trend between the object and the conveyor belt; If the speed of the object is different from that of the conveyor belt, and further divide the direction of the object's relative speed to the conveyor belt, then that direction is the direction of the object's relative motion trend to the conveyor belt.
3. The magnitude of friction between objects on a conveyor belt
Calculate the sliding friction between the object and the conveyor belt. On a horizontal conveyor belt, FN is equal to the size of the object's gravity; On a skewed conveyor belt, FN is equal to the force of the object's gravity along the direction perpendicular to the conveyor belt.
There is no ready-made formula for calculating the static friction force of objects on a conveyor belt, and it is usually determined based on common sense of balance or Newton's second law.

Analysis: (1) When v=0, the object block stops relative to the ground. Assuming that the touch surface is lubricated, the object block moves to the left relative to the conveyor belt, that is, the relative movement trend of the object block is to the left, so the direction of static friction force on the object block is to the right. If the conveyor belt is long enough, the object will accelerate under the effect of static friction until the speed of the object equals the speed of the conveyor belt. After that, the object will no longer be subject to friction and will remain at a constant speed along with the conveyor belt.
If v=0, the object block slides relative to the conveyor belt, and the frictional force on the object block to the right begins to accelerate. If the conveyor belt is long, when the speed increases, the object block will no longer experience frictional force.
(2) When the object moves to the left relative to the conveyor belt, the sliding friction force to the right begins to accelerate. If the conveyor belt is long enough, when the speed reaches equal, the object will no longer be affected by the friction force.
(3) At this time, the object block and the conveyor belt remain relatively stationary, without any relative movement trend, and are not subject to friction.
(4) When the object block moves to the right relative to the conveyor belt, it begins to slow down due to the sliding friction force to the left. If the conveyor belt is long enough, when the speed is reduced to equal, the object block will no longer be affected by the friction force.

Article compilation: Jiangmen assembly line www.zs-chsb.com esun5