Which of the following options is known to reduce friction?

Ball bearings are designed specifically to reduce friction between moving parts. They are used in various mechanical applications where rotational movement is required, such as in wheel hubs, gears, and machinery. The structure of ball bearings allows for smooth rotation by enabling parts to roll over each other rather than slide, which minimizes the resistance caused by friction.

By employing a series of small, hardened steel balls situated between inner and outer rings, ball bearings create a low-friction environment that allows machinery to operate more efficiently. This reduced friction leads to less wear and tear, increases the lifespan of components, and enhances the overall performance of mechanical systems.

The other options, such as car brakes, tire tread, and sandpaper, actually increase friction in their respective applications. Car brakes use friction to slow down or stop a vehicle; tire tread provides the necessary grip on road surfaces, ensuring stability and control; and sandpaper is used to smooth surfaces by creating surface abrasion through increased friction.