To measure the force of friction, let’s do an experiment. Take a dynamometer and attach it to a wooden block that lies on a table. We will pull the dynamometer evenly and horizontally. Under such conditions, two forces will act on the body: the spring elastic force and the friction force. They will be directed in opposite directions, but since the movement is uniform, the modules of these forces are equal. And now, knowing the spring elastic force, we also learn the friction force of the bar on the table.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.