1. The problem statement, all variables and given/known data my teacher says that there is no work done on carrying a bag walking horizontally but there is work done in walking upstairs. why? 2. Relevant equations work is done with motion in the direction of the force/ with displacement. 3. The attempt at a solution when the teacher first asked i answered there is work because it's just like pushing the bag but the difference is that the bag is elevated the other thing that lead me to that was that the force from the legs' direction is forwards and the bag moves forward too, i thought my answer made sense because the displacement was in the direction of the force. later i found out that i was wrong because they said force to be considered was the force of the arm and since the bag wasn't displaced upwards (the direction of the force of the arms); no work. so, i was wrong. i didn't quite accept that because when you illustrate it (| is the person and o is the bag) |o.........|o it obviously shows that the bag was displaced from its original position and moved to the direction of the force of the legs. then someone said (i think it was my teacher or my classmate) that the point of origin was your body and since the bag didn't move away from the body..no displacement no work. that to me finally made sense. then the teacher asked if there was work done walking upstairs; i said none because the bag wasn't displaced away from the body. i was also wrong then. the reason now was that the bag moved up and the direction of the force was also up. then i got confused again because walking up, the bag doesn't move away from your body and how come walking horizontally didn't qualify as work when the bag still moved in the direction of the force!!