Rotational dynamics is one of the introductory experiments for undergraduate students. The leading objectiv e of the experiment is to determine the moment of inertia from the relationship between torque and angular acceleration of a disc by using motion sensors [ 6 ]o r electrical current [ 7 ]. A computerized technique that requires specific software is also used to determine the moment of inertia [ 8 ]. An interesting work, recently proposed by Alam et al [ 9 ], is the modification of the rotational dynamics apparatus made by Pasco t o study the linear coefficient of rotational friction by letting the disc rotate freely after initial impulse excitation and then recording the reducing angular speed. Such an e xperiment could be called a 'let it roll' experiment.