=> Friction is result of the irregularities on the two surfaces in contact of each other.
=> The force of friction is dependent on the irregularities of the surface; if it is greater, then the friction will be greater and if it is smooth, then the friction will be lesser.
=> Effectively, the friction is result of the interlocking of irregularities in the two surfaces.
=> If the two surfaces in contact are pressed harder, then the force of friction will increase.
=> On a frictionless surface, if an object starts moving, it would not stop ever; Without friction, it is not possible to construct a building.
=> Friction produces heat; when a matchstick is rubbed against the rough surface, it catches fire.
Substances Reducing Friction
=> The substances that reduce friction are known as lubricants. E.g. when oil, grease, or graphite is applied between the moving part of a machine, then it creates a thin layer; resultantly, moving surfaces do not directly rub against each other that ultimately reduces friction.
=> When a body rolls over the surface of another body, the resistance to its motion is known as the rolling friction. The rolling reduces the force of friction.
=> The frictional force exerted by fluids is known as drag.
=> The frictional force, on an object in a fluid, is dependent on its speed with respect to the fluid.
=> The frictional force depends on the shape of the respective object and also on the nature of the fluid.
=> Fluid friction is minimized by giving suitable shapes to the bodies moving in fluids.