The discussion centers on the interpretation of work done in a physics scenario involving a person lifting a mass using a pulley system. It is established that the work done by the person on the mass is positive, as the force exerted is in the same direction as the displacement. Conversely, the work done by the mass on the person is negative, following Newton's third law. The tension in the rope is clarified as a tensor that results in a force depending on the object in the free-body diagram (FBD), which should focus on one object and its external forces.
PREREQUISITESStudents of physics, educators teaching mechanics, and anyone seeking to understand the dynamics of forces in lifting systems.
There is no such thing. There is the "work done by the person on the mass". That work is positive because the force by the person on the mass (or rather, the rope) is in the same direction as the displacement when the mass is lifted. Then there is the "work done by the mass on the person", which would be the opposite because it is the same displacement but the force is the Newton 3 pair of the force of the person on the mass, i.e., it is equal in magnitude and opposite in direction.patric44 said:
so the person work on the mass is + , but i have a question here what is the arrow in front of the person indicates , its some how strange that its opposite to the tension force ? as if its indicating the acceleration of the system indicating a negative work or something ?!Orodruin said:
Tension in itself is not a force, it is technically a tensor that gives you a force depending on which object you are drawing the FBD for. If you are drawing the FBD for the person, then the force resulting from the tension is directed to the right (it is the tension in the rope multiplied by the direction of the rope away from the object you are drawing the FBD for). You should forget you ever saw that figure, it is a very bad figure that just seems designed to confuse.patric44 said:
