CLASS 8 CH SOUND PRESENTATION

2. WHAT IS
SOUND?
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 sound 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.

3. WHAT ARE WAVES?
A wave is a disturbance of one or more fields such that the field values oscillate repeatedly about a stable equilibrium value. If
the relative amplitude of oscillation at different points in the field remains constant, the wave is said to be a standing wave.
Mechanical waves are waves that travel through a material medium.
It is of two types: depending on the direction of motion of the particle of the medium and the wave propagation:
*transverse
*longitudinal

4. TRANSVERSE
A transverse wave is a
moving wave that is made up
of oscillations happening
perpendicular to the direction
of energy transfer. It can also
mean that it is a wave that
causes the medium to vibrate
amazingly at right angles
perpendicular to the direction
in which they travel parallel to
each other.

5. LONGITUDINAL
A longitudinal wave is
a wave in which the particle
movement is parallel to the
direction of
the wave propagation.
This means that the particles
move left and right which in
turn makes the other particles
start to oscillate.
... Longitudinal waves are also
called pressure waves, and
sound waves are the most
common kinds.

6. HOW SOUND
IS PRODUCES
BY HUMANS?
In humans, the sound is
produced by the voice
box or the larynx. The
voice box is at the upper
end of the wind pipe.
Two vocal cords are
stretched across the
voice box (or larynx) in
such a way that it leaves
a narrow slit between
them. Air passes through
this slit. When air from
the lungs is forced out
through the slit, the
vocal cords vibrate to
produce sound.

7. HOW DO STRING TELEPHONE WORK?
Whenyou speakintothecup,thebackof thecupvibrates;thevibrationextendsintothe string,likea pushona
slinky;thesoundwaves,or vibrations, movethroughthe string.

8. HUMAN EAR
Outer ear = pinna: collects sound from the surroundings.
Sound passes through a tube called an auditory canal.
Eardrum (tympanic membrane) → vibrates when the sound incident.
Vibrations are sent to the inner ear, from there it goes to the brain as signals via the auditory
nerve.

9. AMPLITUDE,TIME PERIOD
AND FREQUENCY
Thenumberof oscillationspersecondiscalledthefrequencyof oscillation.
Frequencyisexpressedinhertz. ItssymbolisHz.A frequencyof 1 Hzisone
oscillationpersecond.If anobjectoscillates20 timesinonesecond,what
wouldbe itsfrequency?Youcanrecognisemanyfamiliarsoundswithout
seeingtheobjectsproducingthem.Howisit possible?Thesesoundsmustbe
differentto enableyouto recognisethem.Haveyou everthoughtwhatfactors
makethemdifferent?Amplitudeandfrequencyaretwoimportantproperties
of anysound.

10. AMPLITUDE,TIME PERIOD AND FREQUENCY OF VIBRATION
The maximum distance to which the bob of a vibrating pendulum goes from its central position is
called amplitude of vibration or amplitude of oscillation
The maximum displacement of a vibrating object from its Central position is called the amplitude of
vibration.
The time taken by pendulum bob to complete one vibration or one oscillation is called the time period
of pendulum.
The time taken by a vibrating object to complete one vibration is called its time period.
The number of vibrations or oscillations made in one second is called the frequency of vibration.
The unit of frequency of vibration or oscillation of a vibrating object is hertz.

12. LOUDNESS AND PITCH
Volume or loudness of a sound depends on the amplitude. The force with which an object is
made to vibrate gives the loudness.
The number of oscillations per unit time. Directly proportional to frequency.

13. AUDIBLE AND INAUDIBLE SOUND
.

14. NOISE POLLUTION
.

15. WHAT IS NOISE POLLUTION?
Noise pollution, also known as environmental noise or sound
pollution, is the propagation of noise with harmful impact on
the activity of human or animal life. The source of outdoor
noise worldwide is mainly caused by machines, transport,
and propagation systems. Noise pollution can cause health
problems for people and wildlife, both on land and in the sea.
From traffic noise to rock concerts, loud or inescapable
sounds can cause hearing loss, stress, and high blood
pressure. Noise from ships and human activities in the ocean
is harmful to whales and dolphins that depend on
echolocation to survive.

16. HOW TO REDUSE
NOISE
POLLUTION?
 Turn off Appliances at Home and offices
 Shut the Door when using noisy Machines
 Use Earplugs
 Lower the volume
 Stay away from Noisy area
 Follow the Limits of Noise level
 Control Noise level near sensitive areas
 Go Green by planning trees