Types of friction

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We all slow down our vehicles whenever needed by applying brakes.Do you know why a vehicle slows down when brakes are applied?

Not only vehicles any object moving on the surface of another object slows down and stops without any external force acting on it because of "FRICTION".Before going to types of friction, lets know about friction. According to law of physics any object in the world can't be frictionless

FRICTION[edit]

Forces on an object in motion

Forces and motion of object. Friction is a force that opposes the motion of two contacting surfaces

LAWS OF FRICTION 

1.Friction depends on the hardness or roughness of the contacting surfaces.Fluid friction depends on the viscosity (thickness)of the fluid 2.Friction is directly proportion to the normal force pressing the contacting forces together. 3.Friction does not depend on the area of the contacting surfaces. 4.In the case of sliding,friction is reduced at very high relative speeds which in the case of fluid friction,it increases with increase in relative speed of movement.

To stop a object in motion a force must act on it in the opposite direction of motion, the force that opposes the motion of the object is called as frictional force.

look at the diagram. At first the block is at rest, then the pushing force keep the block moving. As the block slides over the surface frictional force acts on it in the opposite direction. Units of friction is Newtons, because friction is also a force and units of force is Newtons.

Friction generally depends on weight of the object and nature of the surface between the moving object and supporting surface.

TYPES OF FRICTION[edit]

Different types of motion of the object gives rise to different types of friction.Generally there are 4 types of friction they are Static friction, Sliding friction, Rolling friction, Fluid friction.Lets discuss about each type of friction in detail.

STATIC FRICTION[edit]

Static friction exists between a stationary object and the surface on which it is resting.It prevents an object from moving against the surface.

Examples: static friction prevents an object like book falling from the desk even if the desk is slightly tilted, it helps us to pick up an object without slipping through our fingers.

when we want to move an object first we must overcome the static friction acting between the object and the surface on which the object is resting.

A stationary book on surface

SLIDING FRICTION[edit]

Sliding friction occurs between objects as the slide against each other.It acts in the direction opposite to the direction of motion.It prevents the object from moving too fast.It is also called as kinetic friction.

Examples: A book sliding from an inclined desk, A kid sliding on a slide.

When sliding friction is acting there must be another force existing to keep the body in moving, in case of the book sliding from the desk the other force acting is gravitational force.

children sliding on a slide

ROLLING FRICTION[edit]

Rolling friction hinders the motion of an object rolling on a surface, that means it slows down the motion of an object rolling on a surface.

Examples: It slows down a ball rolling on a surface and it slows down the motion of tire rolling on the surface.

Like sliding friction here also another force is required to keep the object in motion, in case of pedaling bicycle the bicyclist provides the force which is required for the bicycle to be in motion.

A ball rolling on a surface

FLUID FRICTION[edit]

Fluid friction is experienced by the objects moving through a fluid.Fluid friction acts between the object and the fluid through which it is moving.It is also called as drag.This force depends upon the object's shape, material, speed with which it is moving and the viscosity of the fluid. Viscosity is the measure of resistance of the fluid to flow and it differs from one fluid to other.

Examples: It slow downs the motion of airplane flying in the air, here the airplanes engine helps the plane to overcome the fluid friction and move forward.

A plane in air

NOTE: sliding friction, rolling friction and fluid friction are types of dynamic friction.