Moment of Inertia

Yesterday, I brushed up the Moment of Inertia also called Angular Mass.

In my textbook, Clamped Bar's moment of inertia is 1/3 times mass of bar times square length of bar.

I first can not understand it, Especially 1/3.


But, Moment of inertia's formula is integral square distance times point mass.

Therefore, In definite integral 1/3 appeares.