To conduct the experiment, the disc is dri ven by manually applying a force in the direction normal to its radius for a short period of time. The force initiates the rotation and the disc is left to rotate freely . The only force that exists during such motion is frictional force that slows do wn the disc. A video of the freely rotating disc is made. The black marker is our tracked point. W e can then acquire the angular speed from Track er . As a result, we can deriv e the linear coefficient of rotational friction from linear regression analysis based on equation ( 2 ) and, therefore, it is possible to calculate frictional torques at various angular speeds from equation ( 1 )