FORCE ;It is the force that  enables us to do any work , to do anything. It is push and pull of the object. Example to close / open the door  pulling of drawers  .

EFFECTS OF FORCE : a) Force can move a stationary body /object . b) Force can stop  a moving body  c) Force can change the  direction of moving the object d)  Force can change the seed  of a  moving body e) Force can change  the shape and size of the object

FORCE ARE OF TWO TYPES  A) Balanced Force :  If the resultant  of applied forces is equal to zero is called balanced force . eg a) In the tug of war  if both the team apply similar magnitude of force in opposite directions, rope does not move in either side. This happens because of  balanced  forces  which  resultant of applied forces becomes zero . b) Balanced forces do not  cause any change  of the state of an object  the balanced forces are equal in magnitude  and opposite in directions   c) Balanced forces can change  the shape and size of the objects  When  forces are applied from both sides over a balloon , size and shape  of balloon is changed.

B)UNBALANCED FORCES ; If the resultant of applied  forces are grater  than zero, the forces are called unbalanced forces An object in the rest can be moved  because of applying unbalanced forces  eg it can move a stationary object , it increase the speed of moving  object , decrease the speed of a moving object  , stops of a moving object  or change the shape /size of the objects

NEWTON’S LAW OF MOTION ;  Newton  studied the idea of  Galileo and gave the laws of motion.

Newtons First Law of Motion : The object remain in the  state of rest or state in uniform motion along with the straight line until  external force is applied . Explanation : If any object is in rest  it will remain in rest until external force is applied or if body is moving with uniform motion in straight line unless external force is applied.

First Law in Everyday life : a) A person standing in a bus  falls backward  when  the bus start moving suddenly this happens because the person and the bus  both are in rest but when it start the in contact with the surface of bus start moving  but upper portion of body is still in rest so if falls backward .  In the same way if bus stops than the lower part of body stops instantly but upper portion remain in motion so it fall ahead . b)  Before  hanging the wet clothes  over laundry line, usually many jerks are given to the clothes  to get dried  quickly. Because  of jerks droplets of water from the pores of  cloth  falls on the ground and reduced amount of water from the pores  help to dry up .

MASS AND INERTIA :  It is the property of the object  because  of which resist  a change in it’s state is called Inertia .Inertia  of an object is measured by mass .Inertia  is directly proportional to mass This means  inertia increases with increase in mass  and vice versa . A heavy object will have  more inertia or lighter the object less the inertia In the other words the natural  tendency of  an object  the resist  the change in the state of motion/ rest of the object is called Inertia . Since a heavy  object has more inertia  thus it is to push/pull a heavy box over the ground than the lighter one so greater the opposing force is needed to  stop a heavy body than the light object

MOMENTUM : Momentum is the quantity  of motion of an object has the product of velocity and  mass is called the momentum. Momentum is denoted as p = mass x velocity  === p= m.v  SI unit is kg – m/sec

Momentum  is related with mass and velocity It means that momentum  of a moving body is directly proportional to mass and velocity . Grater the mass greater the momentum if  velocity is constant . If mass is constant  higher the velocity higher the momentum

Example a) when  a body of 10 kg moving with the velocity of 2 m/sec than momentum is  mass. velocity = 10.2 =20 kg m/sec .

b) A lorry of mass of 4000kg having 2000 kg mass in it  moving the velocity of 2 m/sec than momentum  is 4000+ 2000 = 6000kg than momentum = mass. velocity = 6000.2= 12000 kg m/sec

SECOND LAW OF  MOTION :  Rate of change of momentum of an object is proportional to  applied unblanced force  in the direction of  force

mass of a body= m  initial velocity =u   final velocity =v  change in velocity = v-u

rate of change  of momentum = mass. (change in velocity ) / time = m, (v-U)/t   as  we know  a=(v-u)/t

rate of change of momentum = m.a = F (force)

SI unit of force is Newton : It is the force applied to 1kg of a body such that acceleration produced is 1 m/sec^2

Newton First Law on the basis of Second Law  : According to first law of motion that the body will remain in rest  or will continue moving in the straight line with the uniform motion  unless the external force is applied.

Rate of change in momentum is equal to force  F= m.(v-u)/t  =====>if  F=0====>  m.(v-u)/t=0          ===>       m(v-u)=0 =====> v-u=0  =====> v=u  (no change in velocity)   moving with same velocity if u=o than v=0  means body i remain in rest .

THIRD LAW OF MOTION : To every action there is equal and opposite reaction .

common application ; It helps us to walk on the floor,  the boat moves  back when we deboard , recoils of gun , rowing of boat .

LAW OF CONSERVATION OF MOMENTUM : When two /more bodies act upon  one another, their total momentums remain conserve provided  no external forces are acting

Initial momentum before impact = final momentum after impact

Suppose two objects A and B  each of mass Ma and Mb  are moving with the initial velocity is Ua and Ub  strike each other  for  time t and  start moving with the velocity of Va and Vb respectively

Initial momentum A = MaUa   Initial momentum of B = MbUb

Final momentum A =MaVa   Final momentum of B = MbVb

Rate of change of momentum A , Fa = Ma(Va- Ua)-:- t

Rate of change of momentum of B Fb= Mb(Vb- Ub) -:- t

According  to III rd law of Motion  Fa= -Fb

Ma(Va- Ua) -:- t  = Mb(Vb- Ub) -:- t

Ma( Va- Ua)       =  Mb(Vb- Ub)

MaVa – MaUa     = MbVb- MbUb

MaVa + MbVb  = MaUa + MbUb

Initial Momentum = Final Momentum

Example a) A bullet of mass of 20gm  is fired with the velocity of speed of  150 m/s  from a pistol of mass of 2 kg than the velocity of recoil m1u1 +m2u2 = m1v1 + m2v2

m1= 20 gm= .02 kg  m2=2kg  u1=u2=0 v1= 150 m/s v2 ?

( m1+m2) u1= m2v2 +m1v1======>  ( .02+2) x0 = .02×150 + 2 x v2

0 = .02×150 + 2v2 ===>  v2= – .02×150 -;- 2 = – .01×150= – 1.5 m/s









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