Work and Energy Class 9 PPT

 Page 1


CHAPTER - 11
WORK AND ENERGY
 
                              
                       
 
Page 2


CHAPTER - 11
WORK AND ENERGY
 
                              
                       
 
1) Work :-
    Work is said to be done when a force acts on an object 
and the object is displaced in the direction of force.
    The work done on an object is the product of the force 
applied and the displacement.
    Work done = force x displacement 
                               W = F X s
   The unit of work is joule (J).
    If F is 1 Newton and displacement is 1 metre then the 
work done is 1Nm or 1 joule (J).
   So 1 joule is the amount of work done when a force of I 
Newton displaces an object by 1 metre. 
   Eg :- If a force of 5 N acts on an object is displaced 
through 2 m in the direction of force, then work done is
            5 N x 2 m = 10 Nm  or 10 J
Page 3


CHAPTER - 11
WORK AND ENERGY
 
                              
                       
 
1) Work :-
    Work is said to be done when a force acts on an object 
and the object is displaced in the direction of force.
    The work done on an object is the product of the force 
applied and the displacement.
    Work done = force x displacement 
                               W = F X s
   The unit of work is joule (J).
    If F is 1 Newton and displacement is 1 metre then the 
work done is 1Nm or 1 joule (J).
   So 1 joule is the amount of work done when a force of I 
Newton displaces an object by 1 metre. 
   Eg :- If a force of 5 N acts on an object is displaced 
through 2 m in the direction of force, then work done is
            5 N x 2 m = 10 Nm  or 10 J
   The work done  by a force may be positive or negative.
   The work done by a force is positive if the force and displacement are 
in the same direction.
   The work done by a force if negative if the force and displacement are 
in opposite directions.
   The work done by a force is zero if there is no displacement.
   The work done  by a force is zero if the force is perpendicular to the 
displacement.
   Eg :- When we lift an object the object moves upward in the direction 
of force. Here the work done is positive. But there is the force of gravity 
acting downward on the object. The work done by the force of gravity 
is negative.
   Eg :- A porter lifts a luggage of 15 kg from the ground and puts it on 
his head 1.5 m above the ground. Calculate the work done by him on 
the luggage.
    Mass of luggage m = 15 kg, displacement = 1.5 m,
    Acceleration due to gravity = 10 ms   
    Work done  W = F x s   =  mg x s  =  15 kg x 10 ms    x 1.5 m
                             = 225 kg ms     = 225 N m   = 225 J
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CHAPTER - 11
WORK AND ENERGY
 
                              
                       
 
1) Work :-
    Work is said to be done when a force acts on an object 
and the object is displaced in the direction of force.
    The work done on an object is the product of the force 
applied and the displacement.
    Work done = force x displacement 
                               W = F X s
   The unit of work is joule (J).
    If F is 1 Newton and displacement is 1 metre then the 
work done is 1Nm or 1 joule (J).
   So 1 joule is the amount of work done when a force of I 
Newton displaces an object by 1 metre. 
   Eg :- If a force of 5 N acts on an object is displaced 
through 2 m in the direction of force, then work done is
            5 N x 2 m = 10 Nm  or 10 J
   The work done  by a force may be positive or negative.
   The work done by a force is positive if the force and displacement are 
in the same direction.
   The work done by a force if negative if the force and displacement are 
in opposite directions.
   The work done by a force is zero if there is no displacement.
   The work done  by a force is zero if the force is perpendicular to the 
displacement.
   Eg :- When we lift an object the object moves upward in the direction 
of force. Here the work done is positive. But there is the force of gravity 
acting downward on the object. The work done by the force of gravity 
is negative.
   Eg :- A porter lifts a luggage of 15 kg from the ground and puts it on 
his head 1.5 m above the ground. Calculate the work done by him on 
the luggage.
    Mass of luggage m = 15 kg, displacement = 1.5 m,
    Acceleration due to gravity = 10 ms   
    Work done  W = F x s   =  mg x s  =  15 kg x 10 ms    x 1.5 m
                             = 225 kg ms     = 225 N m   = 225 J
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2) Energy :-
    The energy of an object is its capacity for doing work.
    The unit of energy is the same as that of work that is 
     joule(J).
    1 joule is the energy required to do 1 joule of work.
    1000 J = 1 kilo joule (kJ).
    There are different forms of energy. They are heat energy, light 
energy, electrical energy, chemical energy, mechanical energy 
(potential energy + kinetic energy) etc.
3) Kinetic energy :-
     The kinetic energy of an object is the energy possessed by the 
object due to its motion.
     All moving objects possess kinetic energy. A falling coconut, 
a speeding car, a flying aircraft, flowing water, blowing wind, a 
running athlete etc. possess kinetic energy. 
    The kinetic energy of an object depends upon its speed. An 
object moving faster has more kinetic energy than an object 
moving slower.
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CHAPTER - 11
WORK AND ENERGY
 
                              
                       
 
1) Work :-
    Work is said to be done when a force acts on an object 
and the object is displaced in the direction of force.
    The work done on an object is the product of the force 
applied and the displacement.
    Work done = force x displacement 
                               W = F X s
   The unit of work is joule (J).
    If F is 1 Newton and displacement is 1 metre then the 
work done is 1Nm or 1 joule (J).
   So 1 joule is the amount of work done when a force of I 
Newton displaces an object by 1 metre. 
   Eg :- If a force of 5 N acts on an object is displaced 
through 2 m in the direction of force, then work done is
            5 N x 2 m = 10 Nm  or 10 J
   The work done  by a force may be positive or negative.
   The work done by a force is positive if the force and displacement are 
in the same direction.
   The work done by a force if negative if the force and displacement are 
in opposite directions.
   The work done by a force is zero if there is no displacement.
   The work done  by a force is zero if the force is perpendicular to the 
displacement.
   Eg :- When we lift an object the object moves upward in the direction 
of force. Here the work done is positive. But there is the force of gravity 
acting downward on the object. The work done by the force of gravity 
is negative.
   Eg :- A porter lifts a luggage of 15 kg from the ground and puts it on 
his head 1.5 m above the ground. Calculate the work done by him on 
the luggage.
    Mass of luggage m = 15 kg, displacement = 1.5 m,
    Acceleration due to gravity = 10 ms   
    Work done  W = F x s   =  mg x s  =  15 kg x 10 ms    x 1.5 m
                             = 225 kg ms     = 225 N m   = 225 J
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2) Energy :-
    The energy of an object is its capacity for doing work.
    The unit of energy is the same as that of work that is 
     joule(J).
    1 joule is the energy required to do 1 joule of work.
    1000 J = 1 kilo joule (kJ).
    There are different forms of energy. They are heat energy, light 
energy, electrical energy, chemical energy, mechanical energy 
(potential energy + kinetic energy) etc.
3) Kinetic energy :-
     The kinetic energy of an object is the energy possessed by the 
object due to its motion.
     All moving objects possess kinetic energy. A falling coconut, 
a speeding car, a flying aircraft, flowing water, blowing wind, a 
running athlete etc. possess kinetic energy. 
    The kinetic energy of an object depends upon its speed. An 
object moving faster has more kinetic energy than an object 
moving slower.
  The kinetic energy possessed by an object of mass m and 
moving with uniform  velocity v is
                       
              E  =       mv
                        
   Eg :- An object of mass 15 kg is moving with a uniform 
velocity of 4 ms   . What is the kinetic energy possessed by 
the object ?
   Mass of the object m = 15 kg.
   Velocity of the object  v = 4 ms 
                E  =      mv    
                     =      x 15 kg x 4 ms   x 4 ms     
                     = 120 J
    The kinetic energy of the object is 120 J  
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