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Angular momentum is also known as the moment of momentum

consider a rigid body rotating about a fixed axis with an angular velocity of $ω$, whose moment of inertia is I

the definition of I is the sum of the products of the mass and the square of the perpendicular distance to the axis of rotation of each particle in a body to the axis of rotation.

i.e

$I=∑mr_{2}$

consider the rigid body is made up of particles each of mass m

then the moment of momentum ( call it L) of each particle

$L=momentum×r$

where r is the perp. distance from the axis

$∴L=mvr$

where v is the linear (tangential) velocity

but for angular motion

$v=rω$

so

$L=mrrω=mr_{2}ω$

For the total angular momentum we have to sum up all the particles

$L_{T}=∑mr_{2}ω$

$L_{T}=ω∑mr_{2}$

$L_{T}=Iω$

so angular momentum is moment of inertia $×$ omega in vectors the formula is

$L=r×mv$

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