Ball bearings are used in bicycles, cars, etc., because

Ball bearings are utilized in mechanical systems like bicycles and cars to minimize friction between the wheel and axle. Friction arises from surface irregularities that lock together when in contact [1]. In a standard sliding contact (like a bushing), the contact area is relatively large, leading to higher resistance. Ball bearings replace this sliding motion with rolling motion. According to Hertzian contact theory, the balls in a bearing make contact with the races at specific, minute points or small elliptical areas [2]. This significantly reduces the effective area of contact compared to sliding surfaces. Because rolling friction is much lower than sliding friction—often by up to 95%—the reduction in the effective contact area allows the wheel to spin more freely with minimal energy loss and heat generation.

Sources

1. [1] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 5: Exploring Forces > Activity 5.3: Let us investigate > p. 68
2. [2] https://ntrs.nasa.gov/api/citations/19810023007/downloads/19810023007.pdf