We went for an early Christmas tea and I found a cheap spinning top in a cracker. I applied a torque to get it into motion. Angular momentum is the product of the angular velocity and the moment of inertia. Inertia is the property of mass that is resistance to changes in linear motion. But when rotated, the further away an equal sized mass is, the harder it is to change its motion. So moment of inertia is the integrated product of mass and distance from the centre. The top will slow down when friction causes a big enough torque to cause an appreciable rate of change of angular momentum. It did stop spinning in the end.
