8th Class Science Friction Notes - Friction

Friction

·                     Friction is a force that opposes the motion. It acts on both the surfaces.

·                     Friction depends on the nature of surfaces in contact.

·                     The factors that affect friction are:

·                     For a given pair of surfaces friction depends upon the state of smoothness of those surfaces.

·                     Friction depends on how hard the two surfaces press together.

·                     The force required to overcome friction at the instant an object starts moving from rest is a measure of static friction. The maximum value of static friction, when motion is impending, is sometimes referred to as limiting friction.

·                     The force required to keep the object moving with the same speed is a measure of sliding friction. It comes into play when an object is sliding over another. Sliding friction is smaller than static friction.

·                     When one body rolls over another body, rolling friction comes into play. Rolling friction is smaller than the sliding friction.

·                     Friction is a necessary evil. If friction force is not present, it becomes almost impossible to stop a moving object.

·                     Friction is sometimes useful and sometimes it is undesirable.

·                     Friction can be increased by

·                     The sole of the shoes and the tyres of the vehicle are treaded to increase friction.

·                     Friction can be reduced by

·                     Fluids exert force of friction on objects in motion through them. The frictional force exerted by fluids is called drag.

·                     The frictional force on an object in a fluid depends on three factors ?

·                     Fluid friction can be minimised by giving streamline shapes to bodies moving in fluids.