Sound Video Lecture | Science Class 8

0:0:0: imagine a world without sound no
0:0:3: laughter no music no birds
0:0:6: chirping sound is everywhere around us
0:0:9: making our world Lively and
0:0:11: vibrant but have you ever wondered how
0:0:14: sound is
0:0:15: produced how does it travel from one
0:0:17: place to another how do we hear sound
0:0:22: why are some sounds louder than others
0:0:25: we shall discuss these questions in this
0:0:28: video sound is produced produced by a
0:0:30: vibrating body let us start with the
0:0:33: first question how is sound produced to
0:0:37: answer this we need to understand what
0:0:39: sound is sound is a form of energy that
0:0:43: is produced by the vibration of an
0:0:45: object what is
0:0:47: vibration vibration is the two and fr of
0:0:50: back and forth motion of an object when
0:0:53: an object vibrates it disturbs the air
0:0:56: around it and creates sound waves these
0:0:59: these sound waves travel through the air
0:1:1: and reach our ears our ears then convert
0:1:5: these sound waves into signals that our
0:1:7: brain can understand this is how we hear
0:1:12: sound let us try an activity take a
0:1:16: metal ball and pour water in it now let
0:1:19: us try to strike
0:1:25: [Music]
0:1:26: it here we can see that the ball is
0:1:29: vibrating and giving off a sound we
0:1:32: closely look at the surface of water we
0:1:35: can see waves being formed and water is
0:1:38: coming out of the
0:1:40: ball to properly see the sound
0:1:42: vibrations we can take an example of
0:1:44: singing ball we can properly see how
0:1:48: vibrations are being made through
0:1:49: movement of water the metal ball is a
0:1:52: special example of a vibrating object
0:1:55: that produces sound when you strike the
0:1:58: ball it vibrates and produces sound it
0:2:1: also creates waves on the surface of
0:2:4: water these waves are the visible
0:2:6: representation of sound waves but not
0:2:10: all objects vibrate in the same way some
0:2:13: objects vibrate faster some slower some
0:2:17: objects vibrate more some less these
0:2:21: differences affect the quality and
0:2:23: quantity of
0:2:24: sound some objects produce high pitched
0:2:28: sounds
0:2:32: some low pitched
0:2:34: [Music]
0:2:37: sounds some objects produce loud
0:2:41: [Music]
0:2:44: sounds these differences depend on the
0:2:46: frequency and amplitude of
0:2:49: vibration now after we have heard how
0:2:52: sound is produced by
0:2:54: instruments but you must be wondering if
0:2:56: sound is produced by vibrations how are
0:2:59: humans able to produce it we humans are
0:3:3: able to produce sound because we have a
0:3:5: organ made specially for producing sound
0:3:8: it is present in upper portion of our
0:3:10: neck its scientific name is
0:3:13: larynx but we normally call it the voice
0:3:16: box of the body two vocal codes are
0:3:20: stretched across the voice box or larynx
0:3:22: in such a way that it leaves a narrow
0:3:24: slit between them for the passage of air
0:3:28: when lungs are forced to pass air
0:3:29: through larns these vocal Cordes stretch
0:3:32: and
0:3:33: vibrate this produces sound waves the
0:3:37: muscles attached to vocal Cordes can
0:3:39: make them tight or loose when the vocal
0:3:42: Cordes are tight and thin we get a high
0:3:44: pitched sound the length of vocal codes
0:3:48: also cause the changes in voice the
0:3:51: vocal codes in men are about 20 mm long
0:3:55: in women these are about 15 mm long
0:3:59: children have very short vocal
0:4:1: Cordes this is the reason why the voices
0:4:4: of men women and children are
0:4:7: different sound needs a medium for
0:4:10: propagation to understand this let us
0:4:13: try a simple activity hold a long metal
0:4:17: rod ask your friend to hold it at one
0:4:19: end and you go to the other end now make
0:4:22: your friend tap the rod with a hammer
0:4:25: you will hear a sound now touch your ear
0:4:29: with your of Rod and ask him to tap
0:4:31: again this time you will hear a sound
0:4:34: and it will be louder than before we can
0:4:37: understand that sound can travel through
0:4:39: air as well as solid we can testify that
0:4:43: by making a toy
0:4:44: phone take a long string and to plastic
0:4:48: cups now attach the ends of string to
0:4:51: the cups now ask your friend to go as
0:4:54: far as possible with one cup try
0:4:57: speaking into the cup your friend will
0:5:0: be able to hear it even if you are far
0:5:3: away hence sound travels through strings
0:5:6: also now here is the fun part using a
0:5:11: scissor cut the string now try to speak
0:5:15: to the cup again you will notice that he
0:5:18: can't hear you again this gives proof
0:5:21: that sound needs a medium to travel when
0:5:24: there is no medium string between the
0:5:26: cups there will be no propagation of
0:5:28: sound
0:5:32: conclusion we were able to understand
0:5:35: the importance and production of sound
0:5:38: we came to know why larynx is called the
0:5:40: voice box of human body we were also
0:5:44: able to deduce that sound needs a medium
0:5:46: to travel by making a toy
0:5:48: telephone so we can say that sound is a
0:5:51: wave that is produced by
0:5:54: vibrations we hope that you have
0:5:56: understood the concept of sound now
0:5:59: here's a secret on how you can study
0:6:1: effectively with the urv app you can
0:6:4: learn with chapter notes watch video
0:6:7: lectures and solve ncer based McQ tests
0:6:11: of this chapter on
0:6:12: urv and that's not all you also get
0:6:15: amazing courses for Class 8 and much
0:6:18: more for your class 8
0:6:20: preparation thank
0:6:22: you