Answer: Ball bearings
Explanation: Friction is according to the law of physics, a force that appears as a resistance that a surface has towards the other surface when moving. This means that in the case of smooth surfaces, the friction is small, while in surfaces with different types of particles, such as sand, tire tread or the like, friction increases because these particles or irregularities on the surface contribute to friction.
So in these options, car brakes increase friction because it is the goal of the brakes, that the friction slows down the car or stops it.
The tire tread also contributes to increased friction, as they are designed to have the necessary friction for safe driving, so as not to slip, especially at high speeds. In such cases, the friction caused by the design of the tire tread profile prevents slipping.
Sand paper is a paper with applied granules of sand on it, which serves to align the surfaces, to become smooth. The surfaces that have become smooth in this way have very little friction, but the sand paper that caused it by its action has great friction, because the action of the friction force from the sand paper on the surface makes it possible to make the treated surface smooth.
What is designed to reduce friction are ball bearings. These are machine parts that are part of the machine assembly, so that the other parts of the machine assembly are movable and do not get damaged during use. Ball bearings serve as a connection between other machine parts within the assembly, and are designed as small balls that rotate and move along the bearing, they are lubricated with oil and thus reduce reducing friction.
