You will be given a definition of a task first, then some input of the task.
In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

Schwinger worked out a model of this operator by considering it as two uncoupled harmonic oscillators and showed that combinations of them satisfy the same commutation relations as this quantity. One theorem states that matrix elements of tensor operators in eigenstates of the operator of this quantity can be written as a coefficient term times a term independent of this quantity; that is the WignerEckart (*) theorem. The isotropy of space guarantees conservation of this quantity, and this quantity is the generator of rotations. Spherical harmonics are eigenstates of the operator of this quantity which is time integral of torque. For 10 points, name this quantity given by angular frequency times the moment of inertia, one type of which is spin.
Output:
Science