Class – 9 Science
Chapter 13 – Sound
Revision Notes
Headings
1. Sound
2. Vibration/oscillatory motion
3. Important terms related to vibration & sound
i. Oscillation
ii. Amplitude
iii. Time period
iv. Frequency
4. Propagation of sound
i. Wave
5. Formation of compressions and rarefactions in a sound wave propagation
6. Sound as a wave
i. Mechanical wave
ii. Longitudinal wave
iii. Pressure wave
7. Diagram for a sound wave
8. Wavelength of a sound wave
9. Speed of sound wave
10. Characteristics of sound
i. Loudness
ii. Pitch
iii. Quality
iv. Intensity
11. Audible & inaudible sound
i. Infrasound
ii. Audible sound
iii. Ultrasound
iv. Application of ultrasound
12. Sound production by human beings
13. Sound hearing by human beings
14. Reflection of sound wave
i. Laws of reflection of sound
15. Echo
16. Reverberation
17. Advantages of multiple reflections of sound wave
18. Noise & Music
19. Noise Pollution
, • Sound :-
A sound is a form of energy that is produced when any object vibrates.
When we strike a tuning fork or a stretched rubber band, it vibrates and produces
sound.
The human voice is produced because of the vibration of the vocal cords.
String instruments produce sound as their strings vibrate.
• Vibration/oscillatory motion :-
Vibration is the to-and-fro or back-and-forth motion of an object. This type of
motion is also known oscillatory motion.
Depending upon the different patterns of vibrations, different sounds are produced.
Sound cannot be produced without any vibration.
Extreme Extreme
Position Position
Mean
Position
TO and FRO motion of a hanging ball
• Important terms related to vibration and sound :-
i. Oscillation :- In oscillatory motion, when an object starts moving from the mean
position and after reaching both the extreme positions, it comes back to the same
mean position. This motion is called one oscillation or one cycle.
ii. Amplitude :- The maximum displacement of an object from its mean position is
called amplitude. The SI unit of amplitude is meter (m)
iii. Time Period :- The time taken by an object to complete one oscillation is called time
period of the oscillatory motion. The SI unit of time period is second.
iv. Frequency :- The number of oscillations completed in one second is called frequency.
The SI unit of frequency is Hertz (Hz).
𝟏 Where, f = frequency
𝒇=
𝑻 T = Time period
Chapter 13 – Sound
Revision Notes
Headings
1. Sound
2. Vibration/oscillatory motion
3. Important terms related to vibration & sound
i. Oscillation
ii. Amplitude
iii. Time period
iv. Frequency
4. Propagation of sound
i. Wave
5. Formation of compressions and rarefactions in a sound wave propagation
6. Sound as a wave
i. Mechanical wave
ii. Longitudinal wave
iii. Pressure wave
7. Diagram for a sound wave
8. Wavelength of a sound wave
9. Speed of sound wave
10. Characteristics of sound
i. Loudness
ii. Pitch
iii. Quality
iv. Intensity
11. Audible & inaudible sound
i. Infrasound
ii. Audible sound
iii. Ultrasound
iv. Application of ultrasound
12. Sound production by human beings
13. Sound hearing by human beings
14. Reflection of sound wave
i. Laws of reflection of sound
15. Echo
16. Reverberation
17. Advantages of multiple reflections of sound wave
18. Noise & Music
19. Noise Pollution
, • Sound :-
A sound is a form of energy that is produced when any object vibrates.
When we strike a tuning fork or a stretched rubber band, it vibrates and produces
sound.
The human voice is produced because of the vibration of the vocal cords.
String instruments produce sound as their strings vibrate.
• Vibration/oscillatory motion :-
Vibration is the to-and-fro or back-and-forth motion of an object. This type of
motion is also known oscillatory motion.
Depending upon the different patterns of vibrations, different sounds are produced.
Sound cannot be produced without any vibration.
Extreme Extreme
Position Position
Mean
Position
TO and FRO motion of a hanging ball
• Important terms related to vibration and sound :-
i. Oscillation :- In oscillatory motion, when an object starts moving from the mean
position and after reaching both the extreme positions, it comes back to the same
mean position. This motion is called one oscillation or one cycle.
ii. Amplitude :- The maximum displacement of an object from its mean position is
called amplitude. The SI unit of amplitude is meter (m)
iii. Time Period :- The time taken by an object to complete one oscillation is called time
period of the oscillatory motion. The SI unit of time period is second.
iv. Frequency :- The number of oscillations completed in one second is called frequency.
The SI unit of frequency is Hertz (Hz).
𝟏 Where, f = frequency
𝒇=
𝑻 T = Time period
