FRICTION

FRICTION

·         Friction is force which opposes the relative motion between two surfaces in contact.

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Frictional force always opposes the applied force and change state of motion of an object. Thus, frictional force is in direction opposite to the applied force.

·         Friction is caused by interlocking of irregularities of  the two contact surfaces.

                                 

·         Factors affecting friction are;

        i.   Friction depends on the nature of surfaces in contact.

      ii.   Friction is more between rough surfaces and lesser between smooth surfaces.

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

    iv.   Friction is independent of the area of contact.

SPRING BALANCE

It is a device used for measuring the force acting on an object. It consists of a coiled spring and a pointer moving on a graduated scale. When force is applied, coiled spring stretches and pointer moves along graduation to record magnitude of the force.

·         Static friction is force required to overcome friction at the instant an object starts moving from its resting position/state.

·         Sliding friction is force required to keep the object moving with the same speed. It can be also defined as resistance to the sliding of object/body over another surface.

·         Sliding friction is smaller than static friction because sliding object didn’t get enough time to interlock with contact surface (incase of sliding friction).

Friction: A Necessary Evil

·         Friction is essential and required in many activities as follows;   
    i. It is difficult to hold objects without friction. Example, a glass with grease is difficult to hold as grease reduces friction.

   ii.   We can’t write with pen, pencil, chalks if there is no friction. When we write with pencil, rough surface of paper rubs off some particles of pencil lead/graphite on to paper and appears letters.

 iii.   Friction helps objects to move, stop and change direction.

 iv.   We can’t walk without friction

   v.   Without friction, we can’t construct houses or buildings.

·         Friction on the other hand is evil and not required because

                          i.   Friction wears out materials like soles of shoes, ball bearings, steps of a stair, parts of machine, etc.

                         ii.   Friction produces heat causing wastage of energy and cause damage in machines.

INCREASING AND REDUCING FRICTION

·         We deliberately increases friction by following ways

           i.   Provision of different pattern of grooves in soles of shoes. It is done to provide shoes better grip on the floor, so we can move comfortably.

         ii.   Treaded tyres of car, trucks and bulldozers provide better grip with ground.

       iii.   Scooter, bicycles and automobiles are provided with brake systems. When we press brake lever, brake pads arrest the motion of rim due to friction and thus the wheel stops moving.

·         In some situation we reduce friction in following methods

           i.   Use of carom powder on carom board to reduce friction

         ii.   We apply lubricants like grease, oil and graphite to moving parts of machine in order to reduce friction.

       iii.   Air cushion between moving object and surface on which it moves reduces friction.

       iv.   Wheels and ball bearings also reduce friction by rolling phenomena.

·         Lubricants are substances which reduce friction by forming thin layer on the moving surface which avoiding interlocking of irregularities that leads to friction at greater extent.

·         Rolling friction is the resistance to the movement of an object/body rolling over another surface.

FLUID FRICTION

·         Common term for gases and liquids is fluid.

·         Fluids exert force on the object in motion through them. The frictional force exerted by fluid is called fluid friction or drag.

·         Frictional force on an object in a fluid depends on

              i.   Nature of the fluid

            ii.   Shape of the object

          iii.   Speed with respect to the fluid

To overcome drag, objects are provided with special shape called streamlined. For example shape of an airplane, fishes, birds, etc.