You might have seen a driver of a car or a truck slowing down the vehicle at a traffic signal. You, too, slow down your bicycle whenever needed by applying brakes. Have you ever thought why a vehicle slows down when brakes are applied? Not only vehicles, any object, moving over the surface of another object slows down when no external force is applied on it. This is due to friction-Force that opposes the motion of an object when the object is in contact with another object or surface is called Friction. Force that slows down or stops motion.
Friction is caused by the irregularities on the two surfaces in contact. Object move slowly on rough surface and requires large applied force. Rough surfaces have greater force of friction as compare to smooth surfaces. Learn about rolling friction, sliding friction and Find out how it easier to roll a body than to slide a body over another.
Fluid surfaces also offer resistance against its flow. This resistance, exhibited by a fluid surface, is calledÂ fluid friction.Â The frictional force exerted by fluids is also called drag. When objects move through fluids, they have to overcome friction acting on them. Efforts are, therefore made to minimize friction. Hence they are given streamlined shape. Birds, fishes, airplanes have streamline shape to reduce fluid(air or liquid) friction.