1. During the rotation of the bearing, the pure rolling friction generated by the rotation and revolution of the steel ball in the inner and outer channels.
2. Sliding friction generated by the contact deformation of the steel ball and the inner and outer raceways during the rotation of the bearing.
3. The sliding friction generated at the contact position between the cage and the steel ball and at the contact position between the seal and the inner and outer rings.
4. Viscous resistance of lubricant.
5. Other factors such as poor bearing cleaning and vibration in the measurement environment.