In rotating machines, what type of bearings are most commonly used?

• A. roller bearings
• B. sleeve bearings
• C. ball bearings
• D. magnetic bearings

Answer: (C)

Ball bearings are the most common choice for rotating machines because they provide low friction and good load handling across a wide speed range in a compact, economical package. The rolling contact of balls between the inner and outer races converts sliding friction into rolling friction, which reduces wear and allows high rotational speeds with smooth operation. Their versatility comes from multiple designs—radial, angular-contact, thrust, and seal options—so they can accommodate different combinations of radial and axial loads, speeds, and enclosure requirements.

Roller bearings, while capable of supporting heavier radial loads, involve larger contact areas and can have higher friction in some setups, making them less universally applicable for everyday rotating equipment. Sleeve bearings have no rolling elements and rely on a lubricant film, which means higher starting friction and potential wear at higher speeds, though they’re simple and robust in specific low-speed, high-load situations. Magnetic bearings eliminate contact altogether but require sophisticated control systems and are relatively specialized and costly, so they aren’t the standard in general machinery.