Mi-5 Moment of Inertia


To demonstrate the dependence of the moment of inertia on the distribution of mass with respect to the axis of rotation.


  • Rotor with slide-able masses on long light tube and drive pulley
  • Thin string and weight

Moment of Inertia 1 Moment of Inertia 2

Moment of Inertia Apparatus.


With masses fixed at maximum R, show the (slow) angular acceleration of the system resulting from torque exerted by the tension in the string. Set masses at minimum R and repeat, showing much higher angular acceleration with (approximately*) the same torque.

*Note: Strictly speaking torque is not quite constant because of variation of string tension T=m(g-a), but, because b has been chosen <<Rmin, a<<g for all R's.