MADE BY :-MADE BY :-SHALINI JOSHISHALINI JOSHI

A force that resists motion between two objects that are in contact with each other. Smoother surfaces exhibit less friction, while rougher surfaces exhibit more friction.

The force that resists motion when the surface of one object comes into contact with the surface of another.

Definitions….

Nature of two surfaces in contact.

Area of contact.The normal force with which the two surfaces are pressed.

Static friction

Static friction is friction between two solid objects that are not moving relative to each other. For example, static friction can prevent an object from sliding down a sloped surface. The coefficient of static friction,typically denoted as μs.

Kinetic friction

Kinetic (or dynamic) friction occurs when two objects are moving relative to each other and rub together (like a sled on the ground). The coefficient of kinetic friction is typically denoted as μk, For example putting a book flat on a desk and moving it around is an example of kinetic friction.

 

Types of Friction…

Fluid friction Fluid friction is the interaction between a solid object and a fluid

(liquid or gas), as the object moves through the fluid. The skin friction of air on an airplane or of water on a swimmer are two examples of fluid friction. The frictional force exerted by fluids is also called Drag.

The frictional force on an object in a fluids depends on its speed with respect to the fluid.

The frictional force also depends on the shape of the object and the nature of the fluid.

Rolling Friction Rolling resistance is the force that resists the rolling of a wheel

or other circular object along a surface caused by deformations in the object and/or surface. For examples of rolling resistance is the movement of motor vehicle tires on a road, a process which generates heat and sound as by-products.

Cont…

Friction: A Necessary Friction: A Necessary EvilEvilFriction is a necessary evil because it has Friction is a necessary evil because it has

both advantages & disadvantagesboth advantages & disadvantages

Advantages of frictionAdvantages of friction

The moving friction can only be stopped by The moving friction can only be stopped by applying brakes. Due to lack of friction, it is applying brakes. Due to lack of friction, it is very difficult to drive vehicle of mud.very difficult to drive vehicle of mud.

Tyres of the vehicles have special projections Tyres of the vehicles have special projections & depressions, so as to avoid slipping.& depressions, so as to avoid slipping.

It is becomes difficult to walk on a slippery road due to low friction. When we move on ice, it     becomes difficult to walk due to low friction of ice.

We can not fix nail in the wood or wall if there is no friction. It is friction which holds the nail.

A horse can not pull a cart unless friction furnishes him a secure Foothold.

Cont….

The main disadvantage of friction is that it produces heat in various parts of machines. In this way  some useful energy is wasted as heat energy.

Due to friction we have to exert more power in machines.

It opposes the motion.

Due to friction, noise is also produced in machines.

Due to friction, engines of automobiles consume more fuel which is a money loss.

DISADVANTAGES OF FRICTION

Increasing FrictionIncreasing Friction

As shown in figure the treated tyres of cars, As shown in figure the treated tyres of cars, trucks, and bulldozers provide better grip with trucks, and bulldozers provide better grip with the ground. the ground.

Increase friction by using brake system of Increase friction by using brake system of bicycle and automobiles.bicycle and automobiles.

Kabbadi players rub their hands with soil for a Kabbadi players rub their hands with soil for a better grip of their opponentsbetter grip of their opponents.

There are a number of methods to reduce friction in which some are discussed here.

USE OF GREASE:Proper greasing between the sliding parts of machine reduces the friction.

USE OF BALL BEARING:In machines where possible, sliding friction can be replaced by rolling friction by using ball bearings.

DESIGN MODIFICATION:Friction can be reduced by changing the design of fast moving objects. The front of vehicles and airplanes made oblong to minimize friction.

  USE OF LUBRICANTS:

The parts of machines which are moving over one another must be properly lubricated by using oils and lubricants of suitable viscosity.

METHODS OF REDUCING FRICTION