The discussion revolves around understanding the direction of work in a scenario involving pulleys and forces acting on a mass. Participants are exploring the implications of force direction and work done by different agents in the system.
Some participants have offered insights into the nature of work done by different forces, noting that the work done by the person is positive while questioning the implications of the diagram. Multiple interpretations of the forces and their directions are being explored, with no explicit consensus reached.
There is mention of a potentially confusing diagram that may not accurately represent the forces involved, leading to uncertainty in the discussion. Participants are also considering the implications of Newton's third law in their reasoning.
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:
