Il n'y a pas de force motrice ?

Between points A and B, the ball is moving along a curved track. The forces acting on it are:

• The weight ($\vec{P}$), acting vertically downwards.
• The normal force ($\vec{N}$), acting perpendicular to the track's surface.
• The friction force ($\vec{f}$), acting parallel to the track's surface, opposing the motion.

A driving force is an external force that adds energy to the system to maintain or increase its motion. In this scenario, the problem description does not mention any engine, motor, or external push that would act as a driving force. The ball is assumed to be moving due to an initial push or a change in potential energy.

Based on the typical setup for such physics problems (unless otherwise specified), there is no explicit driving force mentioned or implied that is actively pushing the ball forward against gravity or friction. The motion is governed by gravity, normal force, and friction.

Therefore, you are correct. There is no driving force acting on the ball between points A and B, other than the forces that are already accounted for (weight, normal, friction).