Hi Question 1 i was wondering if there is any method to find the point from which the angular momentum is a conserved quantity. let me e.g. choose the case of a planet moving in an orbit around the sun. In this case, the angular momentum measured from the center of mass as the point of reference is conserved. But if i choose a different point, that is not exactly on the line connecting the planet and the sun, then the angular momentum is varying with time. so how do i found out how to choose this point, if the system is more complex? Question 2 if F is a conservative force field, then the energy is conserved. is the converse, the energy is conserved, therefore we have a conservative force field also true?