The Moment of Inertia is often given the symbol

. It is the rotational analogue of mass. In Newtonian physics the acceleration of a body is inversely proportional to mass. In Newtonian rotational physics angular acceleration is inversely proportional to the moment of inertia of a body. You can think of the moment of inertia as the ability to resist a twisting force or torque.**I**For rotation about a fixed point, the moment of inertia of a body

is given by the sum of all the constituent particles masses**I**multiplied by their radius**m**_{i}from the fixed point squared. ie**r**_{i}The angular momentum of a solid object is just

where**Iω**is the angular velocity in radians per second. Angular momentum in a closed system is a conserved quantity just as linear momentum**ω**(where**P=mv**is mass and**m**is velocity) is a conserved quantity.**v****Some moments of inertia for various shapes/objects**For a uniform disk of radius

and total mass**r**the moment of inertia is simply**m**.**1/2 m r**^{2}For a solid sphere

.**I=2/5 m r**^{2}A point particle of mass

in orbit at a distance**m**from an object has a moment of intertia of**r**.**I=mr**^{2}