PPT: Chapter 12 - Sound, Class 9, Science PDF Download

 Page 1


CHAPTER - 12
SOUND
CLASS :- IX 
MADE BY :- MANAS MAHAJAN
SCHOOL :- K.V . GANESHKHIND PUNE-7
Page 2


CHAPTER - 12
SOUND
CLASS :- IX 
MADE BY :- MANAS MAHAJAN
SCHOOL :- K.V . GANESHKHIND PUNE-7
1) Production of sound :-
Sound is produced due to the vibration of objects.
Vibration is the rapid to and fro motion of an object.
Eg :- The sound of human voice is produced due to the 
vibration of the vocal cords.
A stretched rubber band when plucked vibrates and 
produces sound. 
Activity :- Strike the prongs of a tuning 
fork on a rubber pad and bring it near
the ear. We can hear a sound. If a 
suspended table tennis ball is  touched
with the vibrating prong, the ball is 
pushed away repeatedly. This shows 
that the prong is vibrating and 
vibrating objects produces sound. 
Thread
Vibrating
tuning fork
Table tennis 
ball
Page 3


CHAPTER - 12
SOUND
CLASS :- IX 
MADE BY :- MANAS MAHAJAN
SCHOOL :- K.V . GANESHKHIND PUNE-7
1) Production of sound :-
Sound is produced due to the vibration of objects.
Vibration is the rapid to and fro motion of an object.
Eg :- The sound of human voice is produced due to the 
vibration of the vocal cords.
A stretched rubber band when plucked vibrates and 
produces sound. 
Activity :- Strike the prongs of a tuning 
fork on a rubber pad and bring it near
the ear. We can hear a sound. If a 
suspended table tennis ball is  touched
with the vibrating prong, the ball is 
pushed away repeatedly. This shows 
that the prong is vibrating and 
vibrating objects produces sound. 
Thread
Vibrating
tuning fork
Table tennis 
ball
2) Propagation of sound :-
The sound produced by a vibrating object travels through a 
medium  to a listener. The medium can be solid, liquid or gas.
When an object vibrates, the particles around the medium vibrates. 
The particle in contact with the vibrating object is first displaced from 
its equilibrium position. It then exerts a force on the adjacent particle 
and the adjacent particle is displaced from its position of rest. After 
displacing the adjacent particle the first particle comes back to its 
original position. This process repeats in the medium till the sound 
reaches the ear. 
The disturbance produced by the vibrating body travels through the 
medium but the particles do not move forward themselves.
A wave is a disturbance which moves through a medium by the 
vibration of the particles of the medium. So sound is considered as  a 
wave. Since sound waves are produced due to the vibration of 
particles of the medium sound waves are called mechanical waves.
Page 4


CHAPTER - 12
SOUND
CLASS :- IX 
MADE BY :- MANAS MAHAJAN
SCHOOL :- K.V . GANESHKHIND PUNE-7
1) Production of sound :-
Sound is produced due to the vibration of objects.
Vibration is the rapid to and fro motion of an object.
Eg :- The sound of human voice is produced due to the 
vibration of the vocal cords.
A stretched rubber band when plucked vibrates and 
produces sound. 
Activity :- Strike the prongs of a tuning 
fork on a rubber pad and bring it near
the ear. We can hear a sound. If a 
suspended table tennis ball is  touched
with the vibrating prong, the ball is 
pushed away repeatedly. This shows 
that the prong is vibrating and 
vibrating objects produces sound. 
Thread
Vibrating
tuning fork
Table tennis 
ball
2) Propagation of sound :-
The sound produced by a vibrating object travels through a 
medium  to a listener. The medium can be solid, liquid or gas.
When an object vibrates, the particles around the medium vibrates. 
The particle in contact with the vibrating object is first displaced from 
its equilibrium position. It then exerts a force on the adjacent particle 
and the adjacent particle is displaced from its position of rest. After 
displacing the adjacent particle the first particle comes back to its 
original position. This process repeats in the medium till the sound 
reaches the ear. 
The disturbance produced by the vibrating body travels through the 
medium but the particles do not move forward themselves.
A wave is a disturbance which moves through a medium by the 
vibration of the particles of the medium. So sound is considered as  a 
wave. Since sound waves are produced due to the vibration of 
particles of the medium sound waves are called mechanical waves.
Propagation of sound through air :-
Air is the most common medium through which sound travels. When 
a vibrating object moves forward, it pushes and compresses the air in 
front of it forming a region of high pressure called compression (C). 
The compression moves away from the vibrating object. When the 
vibrating object moves backward, it forms a region of low pressure 
called rarefaction (R). As the object moves to and fro rapidly, it 
produces a series of compressions and rarefaction in the air which 
makes the sound to propagate in the medium.
Page 5


CHAPTER - 12
SOUND
CLASS :- IX 
MADE BY :- MANAS MAHAJAN
SCHOOL :- K.V . GANESHKHIND PUNE-7
1) Production of sound :-
Sound is produced due to the vibration of objects.
Vibration is the rapid to and fro motion of an object.
Eg :- The sound of human voice is produced due to the 
vibration of the vocal cords.
A stretched rubber band when plucked vibrates and 
produces sound. 
Activity :- Strike the prongs of a tuning 
fork on a rubber pad and bring it near
the ear. We can hear a sound. If a 
suspended table tennis ball is  touched
with the vibrating prong, the ball is 
pushed away repeatedly. This shows 
that the prong is vibrating and 
vibrating objects produces sound. 
Thread
Vibrating
tuning fork
Table tennis 
ball
2) Propagation of sound :-
The sound produced by a vibrating object travels through a 
medium  to a listener. The medium can be solid, liquid or gas.
When an object vibrates, the particles around the medium vibrates. 
The particle in contact with the vibrating object is first displaced from 
its equilibrium position. It then exerts a force on the adjacent particle 
and the adjacent particle is displaced from its position of rest. After 
displacing the adjacent particle the first particle comes back to its 
original position. This process repeats in the medium till the sound 
reaches the ear. 
The disturbance produced by the vibrating body travels through the 
medium but the particles do not move forward themselves.
A wave is a disturbance which moves through a medium by the 
vibration of the particles of the medium. So sound is considered as  a 
wave. Since sound waves are produced due to the vibration of 
particles of the medium sound waves are called mechanical waves.
Propagation of sound through air :-
Air is the most common medium through which sound travels. When 
a vibrating object moves forward, it pushes and compresses the air in 
front of it forming a region of high pressure called compression (C). 
The compression moves away from the vibrating object. When the 
vibrating object moves backward, it forms a region of low pressure 
called rarefaction (R). As the object moves to and fro rapidly, it 
produces a series of compressions and rarefaction in the air which 
makes the sound to propagate in the medium.
A vibrating object producing a series of compressions (C) 
and rarefaction (R)
C C C C R R R R