* Static friction was overcome: The chair was initially stationary, meaning the force of static friction was holding it in place. When the 15 Newton force was applied, it overcame the maximum static friction force.
* The frictional force is less than 15 Newtons: Since the chair began to move, the applied force (15 N) was greater than the opposing force of friction.
* We don't know the exact value of friction: We only know the applied force was *greater than* the frictional force. To determine the actual frictional force, we would need more information, such as the acceleration of the chair or the coefficient of friction between the chair and the floor.
In summary: The fact that the chair started moving tells us that the applied force exceeded the maximum static friction force, but we need more information to determine the exact value of friction.
