Quick Revision: Sound Video Lecture | Science Class 8

0:0:0: today we're going to learn about sound
0:0:2: sound is something we hear every day
0:0:4: from the moment we wake up to the moment
0:0:6: we go to sleep it helps us communicate
0:0:9: enjoy music and even stay safe have you
0:0:12: ever wondered how sound is made well it
0:0:14: all starts with vibrations when
0:0:17: something vibrates it moves back and
0:0:19: forth really fast and this creates sound
0:0:22: for example when you hit a school bell
0:0:24: it vibrates and makes a ringing sound or
0:0:27: if you pluck a rubber band it vibrates
0:0:30: and makes a twangy sound even beating a
0:0:32: drum or blowing into a bugle creates
0:0:35: sound through vibrations isn't that
0:0:37: fascinating now let's talk about how we
0:0:41: humans produce sound inside our throat
0:0:44: there's a special part called the voice
0:0:45: box or larynx it has two vocal chords
0:0:48: stretched across it when we breathe out
0:0:51: air rushes through these chords making
0:0:53: them vibrate this vibration creates
0:0:56: sound whether we're talking singing or
0:0:59: even Whispering it's all about those
0:1:1: vibrations in our voice box pretty cool
0:1:4: right ever wonder how sound gets from
0:1:7: one place to another the traveling of
0:1:9: sound is called propagation of sound
0:1:12: sound travels through mediums like
0:1:13: solids liquids and gases but guess what
0:1:17: sound can't travel in a vacuum where
0:1:20: there's no air or matter that means if
0:1:22: you're in space no one can hear you
0:1:24: scream but back here on Earth sound can
0:1:27: travel through the solid string of a kin
0:1:29: telephone through water like whales
0:1:31: using Echoes to find their way and
0:1:33: through the air so we can hear all the
0:1:35: sounds around us all right let's dive
0:1:38: into how our ears catch these sounds
0:1:40: sound waves enter our ear canal and hit
0:1:43: the eardrum making it vibrate these
0:1:45: vibrations are then sent to the inner
0:1:47: ear which sends signals to our brain and
0:1:50: just like that we hear sound when we
0:1:53: talk about sound we know now that it
0:1:55: vibrates that means it has an
0:1:57: oscillatory motion what is an
0:1:59: oscillatory motion the two and fro
0:2:1: motion of an object is known as
0:2:3: vibration and this motion is also called
0:2:5: oscillatory motion now three important
0:2:8: words come up amplitude time period and
0:2:11: frequency amplitude is how far the
0:2:14: vibration moves from its Central
0:2:16: position it's what makes a sound loud or
0:2:18: soft the time period is how long it
0:2:21: takes for one complete vibration and
0:2:23: frequency it's all about how many
0:2:26: vibrations happen in 1 second measured
0:2:28: in hertz more vibrations mean a higher
0:2:31: frequency and this can change the pitch
0:2:33: of the sound we hear speaking of loud
0:2:35: and soft sounds did you know that the
0:2:37: loudness depends on amplitude a bigger
0:2:40: amplitude means a louder sound and what
0:2:42: about the pitch that's determined by
0:2:44: frequency a low frequency gives us a
0:2:47: deep sound like a drum while a high
0:2:49: frequency gives us a high-pitch sound
0:2:51: like a whistle it's all about how fast
0:2:54: those vibrations are happening guess
0:2:56: what not all sounds can be heard by our
0:2:59: ears sounds that have a frequency
0:3:1: between 20 Herz and 20,000 htz are
0:3:3: called audible sounds that's what we can
0:3:5: hear but there are inaudible sounds too
0:3:9: which are sounds with frequency below 20
0:3:11: htz and above 20,000 htz animals like
0:3:14: dogs and bats can hear some of these in
0:3:16: notable sounds which is pretty cool now
0:3:20: let's talk about noise and musical
0:3:21: sounds noise is those unpleasant sounds
0:3:24: we sometimes hear like when everyone
0:3:26: talks at once in a classroom it's made
0:3:29: by irregular vibrations on the other
0:3:31: hand musical sounds are Pleasant and
0:3:33: have regular vibrations like the music
0:3:36: from instruments or someone singing a
0:3:38: beautiful song lastly too much noise
0:3:40: isn't good for us or the environment
0:3:43: it's called noise pollution it can come
0:3:45: from loud Vehicles machines and even
0:3:48: household appliances noise pollution can
0:3:50: make it hard to sleep raise our blood
0:3:52: pressure and even hurt our hearing over
0:3:55: time but don't worry we can reduce noise
0:3:57: pollution by using things like silencer
0:4:0: turning down the volume and planting
0:4:2: trees to block noise we hope that you
0:4:4: have understood the topic you can now
0:4:6: study chapter notes watch video lectures
0:4:8: and solve McQ tests of this chapter on
0:4:11: edev to ensure you score well in your
0:4:13: school exams and that's not all you also
0:4:16: get amazing courses for maths science
0:4:19: English Hindi and much more for Class 8
0:4:22: thank you