Sound is produced by vibrations that propagate through a medium as waves. It travels faster in solids than liquids and gases. The human ear detects sound waves that are converted into electrical signals in the brain. Sound waves have properties like amplitude, frequency, pitch and loudness. Ultrasound and infrasound are inaudible to humans but used by some animals for navigation and communication. Sonar uses ultrasound pulses and their echoes to determine distances underwater.

3. Sound is a vibration that propagates as a typically
audiblemechanical wave of pressure and displacement,
througha mediumsuch as air or water.
WhatisaSound?

4. Sound travels through gases, liquids and solids.
The speed of sound is the maximum in solids,
less in liquids and the least in gases.
 Sound cannot travel through vacuum because
there are no particle to exhibit the properties of
elasticity and inertia in vacuum.

5. Vibration is a mechanical phenomenon whereby
oscillations occur about an equilibrium point. The
word comes from Latin vibrationem
("shaking, brandishing").

7. A Sound is produced because of the vibration.
The organ in human beings that is involved in the
production of sound is Larynx or Voice box.
 It is situated at the upper end of the windpipe . Two Vocal
cords are stretched across the larynx in such a way that it
leaves a narrow slit between them for the passage of air.
There are muscles attached to the vocal cords.
These muscles are vary the tension in the vocal cords.
With the help of these muscles , we can make different
sounds.

8. Structure of Human
EarSound waves are collected by the pinna and then are
directed through ear canal sound waves on striking the
eardrum make it vibrate exactly the same way as the given
sound emitting object. The bones in the middle ear start
vibrating when eardrum vibrates. It helps in magnifying the
vibrations. When the magnified vibrations reach the cochlea
in the inner ear, the fluid in it starts vibrating. These
vibrations are picked up by sensory receptors and are
converted into electrical signals. These electrical signals then
travel to the brain which interprets sound.

9. LongitudinalWaves
In longitudinalwaves, particlesof the medium vibrate
parallel tothe directionof propagationof the waves.

10. TransverseWaves
In transverse waves, particlesof the medium vibrate
perpendicularto the directionof propagationof waves.

11. Amplitude
Amplitudeistheobjectivemeasurementofthedegreeof
change(positiveornegative)inatmosphericpressure(the
compressionandrarefactionofairmolecules)causedby
soundwaves.Soundswithgreateramplitudewillproduce
greaterchangesinatmosphericpressurefromhighpressure
tolowpressure.

12. Frequency
Frequency describes the number of waves that pass a fixed
place in a given amount of time.
Usually frequency is measured in the hertz unit, named in
honor of the 19th-century German physicist Heinrich Rudolf
Hertz.
The hertz measurement, abbreviated Hz, is the number of
waves that pass by per second.

13. Loudness is:
i ) directly proportional to square of amplitude.
ii) inversely proportional to square of distance.
iii) directly proportional to surface area of vibrating body.
iv) directly proportional to the density of medium.
v) more the resonant bodies nearby , more will be the
loudness.
The loudness of sound depends on its amplitude.
LOUDNESS
• Loudnessisexpressedintheunitsdecibel{dB}.

14. Threshold of hearing 0 dB
Quiet living room 20 dB
Refrigerator 40 dB
Normal Conversation 60 dB
Passing Motorcycle 90 dB
Helicopter 110 dB
Rocket launch 180 dB
Examples for Sound Levelsin Decibel

15. PITCHThecharacteristicofsound by which an acuteor shrillnote can be
distinguishedfroma flator grave noteis calledPitch.
The frequency determinesthe shrillness ofa sound.
If thefrequency is higher thesound is shrill and has a higherpitch.
If thefrequency is lower thesound has alowerpitch.
Drum vibrateswith a lowerfrequency, so itproduces a lowpitchedsound.
Lionmakesa low pitchedsound.

16. Audible and
Inaudible Sounds

17. Sounds of frequencies
between 20 – 20,000 Hz
which can be detected
by the human ears. Such
sounds are called audible
sounds.
Audible sounds

18. Inaudible Sounds
Sounds of frequencies less
than 20 vibrations per second
(20Hz) and higher than 20,000
Hz cannot be detected by the
human ears. Such sounds are
called inaudible sounds.

19. Infrasound
Infrasound is sound that is lower in frequency than 20 Hz or cycles per second.
Hearing becomes gradually less sensitive as frequency decreases, so for humans
to perceive infrasound, the sound pressure must be sufficiently high. The ear is the
primary organ for sensing infrasound, but at higher intensitiesit is possible to feel
infrasound vibrations in various parts of the body.
The study of such sound waves is referred to sometimes as infrasonic , covering
sounds beneath 20 Hz down to 0.1Hz and rarely to 0.001 Hz. This frequency
range is utilized for monitoring earthquakes.

20. Whales, Elephants, Rhinos, and Tigers can produce sounds
below 20 hertz. The lower the frequency, the farther the
distance the sound can travel.
Infrasound Animals

21. UltrasoundsUltrasounds are sound waves with frequencies higher than 20,000 Hz.
Ultrasound isused in many different fields. Ultrasonicdevices are used to
detect objects and measure distances. Ultrasound imaging or sonography is
often used in medicine. Ultrasound is used for cleaning, mixing, and to
accelerate chemical processes.
Animals suchas bats use ultrasound for locating prey and obstacles.
Bats use a variety of ultrasonic ranging (echolocation) techniques to detect
their prey. They can detect frequencies beyond 100 kHz, possibly up to
200 kHz.
Toothed Whales , including dolphins, can hear ultrasound and use such
sounds in their navigationalsystem (biosonar) to orient and capture prey.

22. Ultrasound Animals
Animals, such as bats, dolphins, rats, whales and oil birds, use ultrasound to navigate or
communicate. Bats, dolphins and some toothed whales used echolation , an ultrasound
technique that uses echoes to identify and locate objects. Echolation allows bats to navigate
through dark caves and find insects for food.

23. SonarA common use of ultrasound is in underwater rangefinding; this use is also called Sonar
(SOund Navigation And Ranging).
Anultrasonic pulse is generated in a particular direction. If there is an object in the path of this
pulse, part orall of the pulse will be reflected back tothe transmitter as an echoand can be
detected through the receiverpath. By measuring the difference in time between the pulse being
transmitted and the echo beingreceived,it is possible to determine the distance.
Ultrasonic rangefinding is used when distances areshorter and the accuracyofthe distance
measurement is desired to befiner.

24. Presented By:
MD MUSHRAF KHAN
Class 9th