Hello I'm new here. I have an interest in physics and have spent the day educating myself on a few concepts. I've stumbled across the concept of angular momentum and I am struggling to understand a particular aspect... I understand in principle the idea that angular momentum is conserved, however I do not understand the part that says "unless acted upon by an external torque". What would that external torque be? If I put a bicycle upside down and start spinning the wheel with my hand I understand that I am applying a torque to the wheel and creating angular momentum. If I left the wheel to spin it would eventually slow down to a stop. So my questions are: If the wheel has slowed down to a stop, where did the angular momentum go if it is conserved? What external torque is being applied to the wheel when it slows down? Does friction count as a torque? i.e. air resistance etc acting on the wheel - are these torques? And if that does count as torque, please could you explain how? Please go easy on me as the last time I studied physics was over 10 years ago in school. I am just an interested amateur keen to expand my knowledge. Thanks so much.