Friction is a force that resists the motion of objects when they come into contact with each other. It is caused by the roughness of surfaces and the interlocking of microscopic irregularities.
Static friction is the force that prevents an object from moving when a force is applied to it. Kinetic friction is the force that resists the motion of an object that is already in motion.
Friction can be reduced by using lubricants such as oil or grease, polishing surfaces to make them smoother, or by using wheels or rollers to reduce the amount of surface area in contact.
The coefficient of friction is a measure of the amount of friction between two surfaces. It is a dimensionless quantity that represents the ratio of the force of friction to the normal force between the two surfaces.
Friction is present in many everyday activities, such as walking, driving, and playing sports. It is also important in industrial processes, such as braking systems in cars and the operation of machines in factories.