Most rotating machines are equipped with ____ ________.

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

Answer: (A)

Rotating machines rely on bearings to support the shaft with as little friction as possible. Ball bearings use rolling elements (balls) between inner and outer races, which converts sliding friction into rolling friction. This dramatically reduces friction and wear, allowing smooth operation at high speeds and with a range of loads. They’re versatile, compact, and cost-effective, making them the most practical and widely used bearing type for a broad spectrum of equipment—from motors and pumps to gearboxes.

Other bearing types exist for specific situations: roller bearings can handle heavier radial loads but are bulkier and require more space and alignment; sleeve bearings are simple and inexpensive but have higher friction and wear at high speeds; magnetic bearings avoid contact entirely but need complex control systems and higher cost, limiting their use to specialized applications.