FUN LEARNING

1. Soun
d

2. Hi, friends I
am John from
class 8 th and
now we are
going to
discuss about
sound.

3. Soun
d
. Sound is something that you
hear or that can be heard.

4. Sound
produced by
human
beings
In humans sound is
produced by the
voice box or larynx.
It is the upper part
of the windpipe.
Two vocal cords are
stretched across
the voice box
leaving a narrow
slit. When the lungs
force air through
slit it vibrates and
produce sound.

5. Sound requires a medium to
propagate
. Sound travels through solids , liquids
and gases. Sound does not travel in a
vacuum.
Eg. Sound travels through the solid
thread of a can telephone.
A whale listens to the reflected
sound (echo) in water to locate it's
pray.
. We are able to listen to sound
because sound travels in air.

6. Amplitude, time period and
frequency of vibration.
Vibration in the to and fro motion of an object. It
is also called oscillatory motion.
. The maximum displacement of an oscillating
body from its central position is called it's
amplitude.
. The motion of the pendulum from one
extreme position to the other extreme position
and back is called and oscillation.
. The time taken for an oscillation is called
time period
. The number of oscillations per second is
called frequency. The unit of frequency is
Hertz.( Hz)

7. Hi, friends as
you know I
am John
and now
meet my
friend Sofia.
Now we are
going to
discuss about
some
instruments.

9. Manjira
and
Ghatam
Many of you might
have seen the
manjira
(cymbals),the
Ghatam and the
noot (mudpots)and
the kartal.These
instruments are
commonly used in
many parts of our
country. These
musical instruments
are simply beaten or
struck.

10. Ektar
a

11. Jal
Tarang

12. Sofia: Wow
that
instruments
are so nice .
John: Yes, you
are right.
John: Now
let's discuss
about audible
and inaudible
sound.

13. Audible and inaudible
sound.
• Audible sound is a sound which we can hear. It
has frequencies between 20 hertz and
20000 Hertz. (Between 20 and 20000
vibrations per second).
• Inaudible sound is the sound which we cannot
hear. It has frequencies less than 20 hertz
and 20000 Hertz.( Less than 20 vibrations
per second and more than 20000 vibrations
per second).
• Sound whose frequencies are more than
20000 Hertz is called ultrasonic sound. Some
animals like dog's can hear ultrasonic sound.
Bats produced ultrasonic sound.

14. Nois
e
. Unpleasant
sound are
called noise. It
is produced
by
irregular
vibrations.
Eg. If all the
students in the
class speak
together, a noise
is produced.

15. Musical
sound
. Sound which is
pleasing to the
years is called
musical sound. It
is produced by
regular vibrations.
Eg. Sound
produced by
musical
instruments,
sound of a
person.

16. Noise
pollution
The presence
of excessive
and
unwanted
sound in the
environment is
called noise
pollution.

17. Causes of
noise
pollution
noise pollution is
caused by the
sound of vehicles
explosions
including bursting of
crackers machines
loudspeakers. In
home it is caused by
television radio and
music systems at
high volume and
some kitchen
appliances desert
coolers air
conditioners.

18. Harmful
effects of
noise
pollution
noise pollution
causes several
health related
problems like lack
of sleep
hypertension high
blood pressure and
CST extra. A person
explorist to loud
sound continuously
mein get temporary
or permanent
impairment of
hearing.

19. Measures
to limit
noise
pollution
Noise pollution
can be reduced
by using
silencers in
vehicles
industrial
machines and
home
appliances
reducing use of
vehicles horns
running TV radio
and music
system at low

20. Thank
you