Which type of bearing is preferred on rotating machines because of their very low coefficient of friction and maintenance?

• A. Needle bearings
• B. Tapered bearings
• C. Sleeve bearings
• D. Ball bearings

Answer: (D)

Friction is minimized when surfaces roll against each other rather than slide. Ball bearings achieve this by using rolling elements (balls) between the inner and outer races, so the contact is rolling rather than sliding. This rolling contact dramatically lowers the coefficient of friction, allows higher speeds, and reduces heat and wear, which translates to longer life with simpler maintenance.

Plain sleeve bearings rely on sliding contact, which inherently has higher friction and more wear unless continually well-lubricated, making maintenance more demanding. Needle and tapered bearings also use rolling elements, but they are optimized for specific load directions and conditions (compact space, high load, or axial-thrust handling), so they aren’t as universally low-friction and maintenance-friendly as standard ball bearings for rotating machinery. That combination of very low friction and broad maintenance advantages is why ball bearings are the preferred choice.