class 9 science ncert ppt class 9 physics ls sound.

1. Sound
By,
Anish. D
IX’B’

2. Agenda / Topics
• What is Sound?
•Production of Sound
•Propagation of Sound

3. What Is Sound?

4. • Sound is a form of energy.
• We can define a sound wave as a disturbance which travels through some medium.
• Sound is the term to describe what is heard when sound waves pass through a medium to the ear.
• All sounds are made by vibrations of molecules through which the sound travels. For instance, when
a drum or a cymbal is struck, the object vibrates.
• These vibrations make air molecules move. Sound waves move away from their source (where they
came from), traveling on the air molecules. When the vibrating air molecules reach our ears, the
eardrum vibrates, too. The bones of the ear vibrate in the same way that of the object that started
the sound wave.
• These vibrations let you hear different sounds. Even music is vibrations. Irregular vibrations are
noise. People can make very complex sounds. We use them for speech.
• Sound is a mechanical wave.
• It needs a medium to travel. It cannot travel in vacuum.
• It travels in the form of waves
Sound

5. The Process Of Sound Travel:
From A Vibrating Object To Our Ear
Sound is made by the
vibrating object
The sound energy
travels through the
medium (air) in the
form of waves
But the particles do
not move. They
just transfer energy
The sound is picked
up by the ear

6. Production Of Sound

7. Production Of Sound
• Sound is produced through vibration of an object.
•Vibration means a kind of rapid to and fro motion of an object.
•For example:-

8. Propagation Of Sound
Group member name

9. Propagation of Sound
• Particles of the medium do not move. They just transfer energy.
• Sound travels in the form of waves.
• There are Two types of waves:
• Particles’ movement parallel to the
direction of propagation of disturbance
• Ex:- Sound wave
Longitudinal
Wave
• Particles’ movement perpendicular to the
direction of propagation of disturbance
• Ex:- Light wave
Transverse
Wave

10. Compressions And Rarefactions
• When an object vibrates it creates a series of compressions and rarefactions.
• Compression- region of high density of particles
• Rarefaction- region of low density of particles

11. Medium For Travel
Sound needs a
medium to
travel.
Travels in the
form of waves
Can travel
through solids ,
liquids & gases
Fastest in
solids, slowest
in gases
Cannot travel
in vacuum

12. Sound through Solids
Why is the
speed of sound
fastest in solids?
Because in
solids, particles
are close
So, direct
transfer of
energy occurs
Thus, speed of
sound is fastest
in solids

13. Sound through Liquids
Speed of sound is
slower in liquids
compared to
speed in solids
In liquids,
particles are bit
spaced out
This is the reason
of the decrease
of speed

14. Sound through Gases
Speed of Sound
is slowest in
gases
Particles of gas
are widely
spaced out
So, speed of
sound is slowest
in gases

15. Speed of Sound In Different Media
5960
1498
346 0
21456
5392.8
1245.6
0
0
5000
10000
15000
20000
25000
solids(steel) liquids (distilled water) gas vacuum
m/s
km/h