Скачать или смотреть Basic Mechanics 10 - angular momentum of a system of particles

In this lecture I extend the notion of angular momentum to a system of particles. I show that the rate at which the angular momentum of a system changes is equal to the net external torque. The proof has a gap that is not often stated in textbooks - it requires the assumption that the third law holds in its strong form. I discuss how the result survives the fact that the microscopic constituents of a macroscopic body often do not obey the strong form of Newton's third law.

I then discuss the fact that the law can be used even when when the observer is non-inertial in the special case when it translating with its origin fixed with the center of mass of the system. This result is often used in solving problems - but it is often used without any explanation in standard textbooks.