- Why is angular momentum conserved for the following situation
So, I was reading my textbook in the section regarding net torque, and they gave an example of a seesaw with one person at each end, and they said that there is a net external torque due to the force of gravity on each person. I completely understand that; however, when I was reading another section of my textbook, they were talking about the conservation of angular momentum, which only happens when the net torque is zero. So they gave an example of a circular disk that rotates freely in a horizontal plane about a frictionless, verticle axle. On top of that, there is a person who walks slowly from the rim of the disk towards the center. The textbook modeled this problem as conservation of angular momentum problem, but why? Isn't the weight of the person causing an external torque just how the weight of the two people in the seesaw caused a net external torque?