Difference between audible and inaudible sounds - Sound, Class 8 Science Video Lecture

good morning children today we shall
talk about the characteristic of sound
we hear many sounds in our day-to-day
life still we are able to differentiate
most of them easily let us hear few
voices can we figure them out good
morning how are you good morning good
morning how are you good morning how are
you
good morning how are you yes this is a
voice of a lady good morning how are you
this is a voice of a girl good morning
how are you this is a voice of a baby
good morning how are you and lastly this
is a male voice so we see the sound of a
baby is different from that of an adult
even if two sounds are equally loud they
differ in some way we can recognize many
familiar sounds without seeing the
objects producing them for example just
by listening you can figure out whether
it is a male voice or a female voice or
it's your brother's voice in specific
some sounds are loud some are quite
I'll uh bye-bye so why is this
difference there these sounds must be
different to enable you to recognize
them have you ever thought what factors
make them different let us find it out
we already know that the sound is
produced by vibrating bodies the to
infer motion of an object is known as
vibration we also know that the sound
propagates in the form of a wave of
vibration which moves from the source in
this vibration repeats itself after a
fixed interval of time so vibration is
an oscillatory motion let us represent
the sound as a wave form we can say this
is the height of the sound wave how loud
are quite a sound s depends on the
height of the sound waves this is called
the amplitude of vibrations the
amplitude actually tells us how far the
vibrating object is displaced from its
central position while vibrating let us
listen to the sound at different volume
or varying loudness
you
you
ah
if we see the waveform of both the
sounds a loud sound has high waves while
a weak or quiet sound has low waves that
is their heights are different one has a
higher height and one has a lower height
and this height is the amplitude of the
sound the loudness of sound depends on
its amplitude when the amplitude of
vibration is large the sound produced is
loud when the amplitude is small the
sound produced is feeble actually the
loudness of sound is proportional to the
square of its amplitude although
feelings of loudness are different from
person to person now coming to the
number of vibrations made how do we say
our represent whether the vibrations are
slow or fast so the number of vibrations
or oscillations per second is called the
frequency of the oscillation the
frequency is expressed in hertz and its
symbol is HZ for hertz a frequency of 1
hertz is 1 oscillation per second we can
also say 1 Hertz equal to 1 vibration
per second say if an object oscillates
25 times in one second what would be its
frequency yes it will be 25 Hertz so if
the frequency increases it means more
vibration or oscillations in a given
time
you know frequency is also defined as
the number of waves passing through a
point in one second
now listen to the sound
you
here the loudness is kept same still the
sound is coming different so what is
different here the slowness or Highness
of sound is the pitch the pitch of sound
depends how fast the object vibrates
something that vibrates slowly makes a
low-pitched sound something that
vibrates very fast makes a high-pitched
sound for example a sound with the low
frequency will have a low pitch such as
a human's heartbeat or a drum beat a
sound with the high frequency will have
a high pitch such as a dog whistle a
bird makes a high pitch sound
Varis a lion makes a low-pitched roar
however the roar of lion is very loud
while the sound of word is quite feeble
to reiterate the frequency determines
the shrillness or the pitch of a sound
if the frequency of vibration is higher
we say that the sound of shrill and has
a higher pitch
if the frequency of vibration is lower
we say that the sound has a lower pitch
or less shrill now we know sound may be
loud of evil and even pitch may vary
that is high pitched or low pitched but
how we are able to distinguish sounds
which have the same pitch and loudness
timbre is then a general term for the
distinguishable characteristics of a
tone let us understand the term timbre
better for example if a guitar and a
piano play the same node at the same
loudness maybe we won't be able to
distinguish but the experienced
musicians will be able to distinguish
this based on the very Timbers even if
those instruments were playing notes at
the same pitch and loudness can we hear
all the sounds no humans cannot hear
sounds of every frequency the range of
hearing for a healthy young person is 20
to 20,000 Hertz the hearing range of
humans gets worse with age people lose
the ability to hear sounds of higher
frequency as they grow older the highest
frequency that a normal middle-aged
adult can hear is only 12 to 14
kilohertz if the frequency of sound
falls within this range it is called an
audible sound that is the range between
20 to 20 kilohertz do you know why we
cannot hear some sounds while other
living things like a bad can we cannot
detect some sounds which have frequency
below the audible range of hearing that
is less than 20 Hertz or about 20
kilohertz it is said to be an audible
sound sound with the frequency below the
audible range of hearing that is less
than 20 Hertz is known as an infrasound
infrasound and the sound with the
frequency above the audible range of
hearing that is more than 20 kilohertz
is known as an ultrasound ultrasound the
human beings can neither produce
ultrasonic sounds nor can they hear the
ultrasonic sound but you know some
animals like that
produce ultrasonic sound during
screaming
to summarize what we have learned today
now we know the different
characteristics of sound the loudness of
sound depends on the amplitude higher
the amplitude louder the sound the
shrillness a pitch depends upon the
frequency of the vibrations higher the
frequency of vibration higher this pitch
of the sound also the audible range for
humans is roughly between 20 Hertz to 20
kilohertz frequency below 20 Hertz is
called infrasound and frequency above
20,000 Hertz or 20 kilohertz is called
ultrasound these are inaudible to humans
sound is used by many animals to detect
danger warning them of possible attacks
before they happen and you know what is
the study of sound wave known as the
scientific study of sound waves is known
as a cow sticks that is all for today
bye bye kids