kinetic energy and angular momentum
If a rigid body rotates about a fixed axis with angular velocity w, prove that kinetic energy of rotation is T=1/2w where I is the moment of inertia about the axis.
Choose the axis as AB in Fig.9-23. A particle P of mass m will rotate about the axis with angular speed w. Then it will describe a circle PQRSP with linear speed v=w where r is its distance from axis AB. Thus its kinetic energy of rotation about Ab is
and the total kinetic energy of all particles is
where
is the moment of inertia about AB.
The result could also be proved by using integration in place of summation