Friction in physics

 what is friction  explain with example ? 

 It is an  Electromagetic contact force which opposes the relative motion or tendency of motion is called force of friction or simply friction . 

💥friction force always acts in opposite direction of acceleration of motion of the block . 

 This is the state of block when the friction force is acting when the block is moving on the rough surface . 

This is the state of block when the friction force is acting in the tendency of motion ( i.e. about to move but still no any there is movement of block ) .

This is the state of block when there is neither a relative motion nor a tendency of motion . 

How many types of friction  ?

 there are two types of friction  -:

1. static friction -: It is a electromagnetic contact force which opposes force of tendency of motion is called static friction . 

static friction is a self - adjustable force ,  but upto limit . 
The maximum value of static friction is called limiting static friction .  

Along vertical 

fnet = o 

N- mg =0

N = mg

Along horizontal 

F-Frs = m *0 

F = Frs 

this implies that if we apply the force on the block and still not move even after applying the force , then the force which we apply must be equal to the static friction by the ground . 

2. kinetic friction -: It is an electromagnetic contact force which opposes the relative motion b/w the surface in contact is called kinetic friction . 

kinetic friction is directly proportional to normal reaction . 

kinetic friction ∝  normal reaction b/w two body 

frk  ∝ N

frk = μk .N 

here  μk = coefficient of kinetic friction 

* coefficient of kinetic friction is slightly less than coefficient of static friction      . 

 μk < μs 

 μk. N < μs.N 

frk < frL 

* kinetic friction is less than limiting friction . so it is easier to maintain motion then to start . 

laws of limiting friction -:

 limiting friction is directly proportional to the normal reaction acting b/w the two body . 

  I.e. FrL ∝ N 

  FrL  = μs . N

where  μs  = coefficient of static friction 

 μs depend upon nature of surface . 

μ < 1   ( μ read as miu )

The value of  μ always given in the question while solving any numerical . 

limiting friction is independent of Area of contact . 

prove that pulling is easier than pushing ?     

 here,  Frl  is the limiting friction  acting  by  the rough surface  when the bl

along vertical 

fnet = 0

N +Fsinθ - mg = 0

N = mg-Fsinθ 

 

Frl = μs.N

Frl = μs (mg -Fsinθ )

Along horizontal 

Fnet = ma 

Fcosθ  - Frl = m*0

Fcosፀ - ( μmg - μFsinθ ) =0 

F( cosθ + μsinθ) = μmg

F pulling  = μmg ∕  cosθ + μsinθ

This is  the force apply by the man on the block while pulling it. In this case overall value of force is increased because in denominator overall value is increased . 

        pushing case 

here frl  ( friction force ) acts in the opposite direction w.r.t to motion of the block of mass m /

Along vertical 

fnet = 0 

N - ( Fsinθ + mg ) = 0 

N = FsinӨ + mg )

frl = μsN

frl = μmg + μFsinθ

Along horizontal 

Fnet = ma 

Fcosθ - ( μmg + μsinθ ) = 0 

F ( cosθ - μsinӨ ) = μmg 

F = μmg / cosθ - μsinθ

This is the force apply by the man while pushing  it . Here overall value of force is increase because in denominator overall value is decreased as a result overall overall value of force is increased . 

In this way we can say that pulling is easier than pushing . 

find the angle at which the force should be applied for pulling to be minimum ? 

F pulling   = μmg ∕  cosθ + μsinθ

for F to be minimum 

cosθ + μsinθ should be maximum 

for cosθ + μsinθ  to be maximum 

d /dӨ ( cosθ + μsinθ ) = 0 

 - sinθ  + μcosӨ = 0 

sinӨ  = μ cosӨ 

sinӨ  / cosӨ  =  μ 

tanӨ =  μ  

Ө    = tan-1 (  μ ) 

I hope this will helpful for you 

please comment and share so that many one get benefited.

SUMAN KUMAR