• Friction

    Whenever a body moves or tends to move over the surface of another body, a force comes into play which acts parallel to the surface of contact & opposes the relative motion. This opposing force is called friction. Friction is always parallel to the contact surfaces and in a direction that opposes motion or attempted motion of the system relative to each other.

    Friction arises due to the atomic or molecular forces of attraction between the two surfaces at the points of contacts. Simply, we say that it is due to the roughness of the surfaces in contact as shown in figure.

    It is important in many aspects of everyday life. The oil in a car engine minimizes friction between moving parts, but without friction between the tires and the road we couldn’t drive or turn the car. About 20% of the gasoline used in an automobile is needed to counteract friction in the engine and in the drive train.

    Air drag, the frictional force exerted by the air on a body moving through it, decreases automotive fuel economy but makes parachutes work. If friction were totally absent, we could not get an automobile to go anywhere, and we could not walk or ride a bicycle. We could not hold a pencil, and, if we could, it would not write. Nails and screws would be useless, woven cloth would fall apart, and knots would untie.

    Friction is used to heat and ignite matchsticks (friction between the head of a matchstick and the rubbing surface of the match box). Sticky pads are used to prevent object from slipping off smooth surfaces by effectively increasing the friction coefficient between the surface and the object.