There is a ball on the floor of the car. The train starts to move, the ball rolls along the floor

There is a ball on the floor of the car. The train starts to move, the ball rolls along the floor of the carriage. In which direction will the ball move?

The ball relative to the carriage will move in the opposite direction of its movement.

This is due to the property of bodies to maintain their original state, which is called inertia. The ball relative to the ground by inertia remains at rest, and the car begins to move.

A moving carriage cannot be considered an inertial frame of reference, since it moves with acceleration. The car is considered to be a non-inertial frame of reference, relative to which, the inertial force acts on the ball, which is directed in the opposite direction of the car’s movement.

Under the action of this force of inertia, the ball begins to move relative to the carriage.