FRICTION

The common name of gases and liquids is fluids. So we can say that fluids exert force of friction on objects in motion through them.

The frictional force exerted by fluids is also called drag.

Moving objects in fluid must have special shapes because the drag force or the friction force depends on the object’s shape. Therefore, special shapes are designed to minimize the opposing frictional force. Fluid friction can be minimised by giving suitable shapes to bodies moving in fluids.

Friction opposes the relative motion between two surfaces in contact. It acts on both the surfaces.

Friction depends on how hard the two surfaces press together.

Sliding friction is smaller than static friction.

Since the rolling friction is smaller than the sliding friction, sliding is replaced in most machines by rolling by the use of ball bearings. Commonexamples are the use of ball bearings between hubs and the axles of ceiling , Rolling reduces friction fans and bicycles

When one body rolls over the surface of another body, the resistance to its motion is called rolling friction. Rolling reduces friction. It is always easier to roll than to slide a body over another.

The substances which reduce friction are called lubricants.

Spring BalanceSpring balance is a device used for measuring the force acting on an object. It consists of a coiled spring which gets stretched when a force isapplied to it. Stretching of the spring is measured by a pointer moving on a graduated scale. The reading on the scale gives the magnitude of the force.