Trying to get the idea behind this, but it's kind of new thinking all this rotational dynamics. The classical example of conservation of angular momentum is when a ballerina pulls in her arms as she spins to spin faster. The angular momentum theorem tells us: I1*α1 = I2*α2 So as she decreases her moment of intertia from I1 to I2 the angular acceleration MUST increase from α1 to α2 due to conservation of angular momentum. Now an increase in angular acceleration must mean that a torque has acted on her - or must it? I'm not really sure, since the moment of inertia isn't the same before and after. So I wanted to know what role the torques play in this situation. Like in linear dynamics, an example of conservation of linear momentum is often if you throw something heavy away from you. Then according to Newtons 3rd law the force you exert on the heave object it exerts back such that you also get a velocity in the opposite direction. Here a force argument is used, so can't the same be done for the rotational example above?