FEATURES OF LAWS OF MOTION
A particle at rest or moving with uniform velocity relative to an observer is said to be in the state of equilibrium.If a particle at rest continues to be at rest or a particle moving with uniform velocity, continues to move with uniform velocity, the net force acting on the particle is zero. (Newtons 1st Law)According to Newton II law of motion, the rate of change of linear momentum of a particle is equal to the net force on the particle. The direction of the net force on the particle will be in the direction of the change in momentum of the particle and it need not be in the direction of velocity
Newton II lawAccording to the Third Law, every action has an equal and opposite reaction.
Pseudo Force is the Force acting on an object relative to an observer in a non-inertial frame, without any interaction with any other object of the universe. Centrifugal force is a pseudo force experienced radially outward by an object relative to the object, moving in a circular path relative to an inertial frame. The centrifugal force is given by
. (V = speed of object relative to inertial frame)
Friction
The force of friction is a force of contact between two surfaces which acts tangentially to the two surfaces in contact, and opposes or tends to oppose, the relative motion between the two surfaces.
The force of friction is a self adjusting force and is macroscopically a non-conservative force.Types of friction
Static Friction : The force of friction between two surfaces when the two surfaces are at rest relative to each other. Note : When there is no component of external force parallel to the two surfaces in contact with each other, the force of static friction is zero.
The limiting frictional force between two surfaces is given by
s is called the coefficient of static friction between the two surfaces and N is the normal force between the two surfaces.The static frictional force between two surfaces is
f
sN Kinetic friction or Sliding friction or Dynamic frictionKinetic friction the force of friction which acts between two surfaces, only when they slide or slip relative to each other.
The force of kinetic friction between two surfaces (fk) equals the force needed to be applied to one of the surfaces, parallel to the surfaces in contact with other,
such that the two surfaces slide relative to each other with uniform velocity.
The force of kinetic friction between two surfaces is given by
fk=
kNRolling friction comes into play when a body such as a ball rolls on a surface. If
R is coefficient of rolling friction then R <R <S for a given pair of surfaces. Sliding block on a horizontal surface coming to rest : 
If a block having initial velocity u slides on a rough horizontal surface and comes to rest, the acceleration of the block is a = -mkg
Distance travelled by the block before coming to rest is 
time taken by the block to come to rest is
Force needed to just slide the body is 
where f is the angle of friction between the two surfaces.
The minimum possible force among all directions required to just move the body is mg sin
or
where f is the angle of friction. The force must be applied at angle
to the horizontal at an angle equal to angle of friction f.
&font=(font)&format=(format)&size=(size)&color=(color)&font=britanic&format=png&color=hh0000&text=%C2%A9Copyright%20KAPIL%20ARYA%202010.&clientAction=wml:anchor.click&size=15){kind=small}
&font=(font)&format=(format)&size=(size)&color=(color)&font=britanic&format=png&color=bb0000&text=Download%20Solved%20Papers&clientAction=wml:anchor.click&size=15){kind=small}
&font=(font)&format=(format)&size=(size)&color=(color)&font=britanic&format=png&color=bb0000&text=Concept%20Bank&clientAction=wml:anchor.click&size=20){kind=small}