The arms of a Porter governor are pivoted on the governor axis and are each 250 mm long. Mass of each ball is 0.5 kg and mass of sleeve is 2 kg. The arms are inclined at an angle of 30° to the governor axis in the lowermost position, of the sleeve. Lift is equal to 50 mm. Determine the force of friction if the speed at the moment the sleeve starts lifting from the lowermost position is the same as the speed at the moment it falls from the uppermost position.