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# Types of Friction

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 Sub Topics Friction is that where resistance exerted by one body upon the second body in contact and moves or tends to move relative to the first body. There are many types of friction existing. The most popular among them are sliding, rolling, static and fluid friction.

## Different types of friction

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There are many types of forces existing in nature. The most common types of friction are,

## Types of friction forces

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Friction is that where resisting force exerted by one body upon the second body in contact and moves or tends to move relative to first body. There are many types of friction existing. The most popular among them are sliding, rolling, static and fluid friction.

## What Type of Friction is Air Resistance?

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When two bodies rub together friction acts. If there is a lot of friction between the surfaces they grip well. If there is a very little friction the surfaces slip over each other.

Air rubs against a car that slows it down and washes fuel but parachutists rely on air resistance to slow their descent. In these you could see slowing down takes place due to air resistance what we call friction.

## Rolling friction

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Rolling friction is that which occurs when an object is rolled over the surface. If F is the necessary to keep an object rolling at some constant velocity v, the rolling friction coefficient $\mu_R$ is given as

$\mu_R$ = $\frac{F}{L}$
where, L is the load.

## Sliding friction

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Sliding friction is the friction experienced by the body when one body slides over the other.

$F_{k} = U_{k} \ N$
Where,
F = Sliding or kinetic friction
$U_{k}$ = Coefficient of sliding friction
N = Normal reaction due to weight

## Static friction

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We see many a kind of daily activities like a heavy box kept on the road, a car at rest etc. These all tells about the Static friction where two forces are not moving relative to each other. If F is the force applied externally and $f_{s}$ be the force of static friction between the surfaces in contact then $f_{s}$ = F when the body is in equilibrium.

If the applied force is gradually increased, the force of static force also increases and attains the maximum value $f_{max}$. Hence the static friction force is given as,
$f_{s}$ = F = $U_{s}$

Example: When we push a huge object and are unable to do so, we try it harder and harder, after some time it moves suddenly and after its movement we find it easier to push. Let's illustrate this activity:
1. Because of Static friction we will not be able to move the object.
2. When it moves, we have to overcome the kinetic friction which was less than static friction. If the coefficient of static friction is high, it means we need a lot of force to overcome the static condition of the object and to make it move.

## Kinetic friction

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The frictional force that opposes the actual relative motion between two contact forces is called kinetic friction. It is denoted by $f_{k}$ as known as dynamic friction.

Lets observe the kinetic friction activity:

The car will be in motion, when brakes are applied on a moving car the friction parts are forced against the rotating parts of the car. The friction causes the rotation parts to slow down and stop. Just as the energy of rotating parts it is called as kinetic energy, the friction used to stop them is called as kinetic friction.

## Fluid friction

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The friction that exists when the contacting separated by a film of fluid. It arises when a film of the fluid separates the two surfaces and when a layer of the fluid move over each other at different speeds.

Lets see the fluid friction activity:

You could observe the fluid film lubrication. The intervening fluid film is very thin is called boundary lubrication and when the abundance of lubricating fluid is available it is called lubrication.