There is a tricep machine which is basically a pulley, with some rope connected to a stack of weights and a bar for you to push down on using your triceps on the other end of the rope. How is it possible that if I'm 140 pounds, I can lift like 180 or more on that machine? If I want to want the weight of 180 pounds, then I must apply more than 180 pounds of force on the bar. But if I only weigh 140 pounds, won't I just be lifted up off the floor? I thought that I could resolve this by thinking that maybe I was just transferring the gravity of my body onto the bar, but my muscles are providing extra force, but isn't that just an internal force?