If the body is motionless, but some force acts on it, tending to move it, then the friction force will be directed opposite to this force and equal to it in absolute value. With an increase in the external force, the friction force also increases, until it reaches its maximum value (determined by the coefficient of friction and the weight of the body), if the external force exceeds this maximum value, the body will come into accelerated motion.
If the body is moving, the friction force is always directed in the direction opposite to the direction of motion. If the bar is moved to the right, then the friction force is directed opposite to the direction of movement of the bar – to the left.
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