During the project a test rig was constructed in which experiments were performed on radial bearings to evaluate the acoustic emission amplitude and RMS value of the signal. The acoustic emission amplitude depends on the Hertz contact time, i.e. the time it takes for the Hertz contact to roll over its own contact length. When the load remains constant on the bearing the Hertz contact time is directly reliant on the rotational speed of the inner ring of the bearing. Two experiments were performed, one on a spherical roller bearing and another identical experiment on a spherical ball bearing. Throughout both experiments the load on the bearing remained constant and the rotational speed of the inner ring was changed, the response of the speed change was measured using an acoustic emission sensor. The experiments found a quadratic dependency between the amplitude of the acoustic emission signal and the rotational speed of the inner ring. During the experiments the bearings were lubricated using grease and a total of 195 measurements were performed on each type of bearing at 13 different rotational speeds ranging between 1 and 3000 RPM.