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why does everything around us generate
sound also there are a whole variety of
sounds running water a cell phone music
someone's voice Wow
the list of sounds you hear throughout a
given day is endless but when you are
shown what sound looks like inevitably
you are shown something like this which
sounds like this and to me that doesn't
make much sense because you never hear
that sound in the real world in this
branch episode let's try to better
understand what is sound let's start
with a simple sound that was popping an
inflated polkadot balloon this polkadot
balloon is filled with high pressure air
particles and when popped all these
particles rush out and hit the adjacent
air particles those particles hit the
next set of adjacent air particles and
so on thereby creating an expanding
shell of air particles just bouncing
into one another this is called a
pressure wave or sound wave this wave
travels throughout the room and
eventually the bouncing air particles
apply a force to your eardrum which
causes parts of your internal ear to
move then your brain processes this
motion in your internal ear and tells
your cognition that oh this motion in my
ear sounds like a popping balloon let's
rewind go back and take a deep dive into
what this sound wave looks like
even though popping the balloon makes a
relatively simple sound when we take a
cross-section and zoom in on a molecular
level we can see the complex pattern
depicting how the air particles are
bouncing into one another this pattern
is produced within a tenth of a second
after the balloon is popped you may ask
where does this pattern come from well
the high-pressure air particles rush out
and generate a high pressure wave but
when they do they create a low-pressure
void in the balloons Center the air
particles rush back in to fill this void
thereby generating a low pressure wave
when the particles rush back in to fill
this void they rush in too much
thereby creating a second high-pressure
zone this cycle repeats itself and each
time it does it generates a high
pressure and low pressure wave which can
be graphed this graph shows the pressure
waves or wave form produced by popping a
balloon the vertical axis is pressure or
the amount of force the particles bounce
into one another the horizontal axis is
time these high points in the waveform
are called compressions and they're
where the particles are compressed and
bouncing around a lot and thus have a
higher pressure the low points in the
waveform are called rarer factions and
they're where the air particles are more
spread out and not bouncing around as
much and thus have a lower pressure
both the graph and particle animation
help to visualize sound which as we know
is invisible to our eyes the
measurements are taken at a single point
in space in this case the pressure was
measured by a microphone in order for
your speakers to duplicate this sound
the diaphragm in your speakers just have
to move in a similar fashion the entire
sound takes one tenth of a second for
your speakers to duplicate this
visualization is just the first section
of the overall pattern of cycling
compressions and rarefactions produced
from a popping balloon in just this
quick sound there are about fifty of
these cycles if we slow down the sound
to four seconds you can hear some of the
cycles between compression and
rarefaction most sounds last much longer
than this quick duration so in
visualizations of sounds we usually see
the squished version of this graph which
looks like this let's consider another
sound here is a running faucet
the moving water molecules apply a force
to the nearby air particles thereby
causing the air particles to bounce into
one another thus creating a sound wave
the sound wave propagates throughout the
room and hits your eardrum or a
microphone and the waveform looks like
this
the difference between the balloon
popping and the running fossa is the way
the air particles are moved which can be
seen in the shape of the waveform
another difference is that the sound of
running water is continuous whereas the
balloon popping only lasted a tenth of a
second
now let's consider a significantly more
complex sound
this sound of Beethoven's 9th is
constructed from dozens of instruments
each instrument when played applies a
force to the air particles around it
thus causing the air particles to bounce
into one another thereby generating a
sound wave so when the wave forms of
different instruments meet in the air
they combine to make a new unique wave
form or sound wait wait wait let's
actually rewind and clarify three quick
things first
this animation properly shows how a
sound wave is a sequence of alternating
compressions and rarefactions
however it doesn't show how sound
propagates in all directions it
propagates kind of like this as an
expanding sphere so just keep that in
mind
also second with this animation it looks
like the particles are traveling however
in reality it is the force of the air
particles that is traveling and this
propagation of force along with the
alternating compressions and
rarefactions is what constitutes a sound
wave take a look at the video how sound
travels to better conceptualize this
bouncing like movement of air particles
and finally third this sound waveform is
just a quick snapshot of what the entire
sound wave looks like it's about four
thousandths of a second in duration to
say it differently there would be 440 of
these waveforms hitting your ear in one
second or to say technically the
frequency of this violin sound is 440
Hertz or to say it musically
it is a musical note a okay so now that
we have those details clarified let's
jump back to where we were so when the
wave forms of different instruments meet
in the air they combine to make a new
unique wave form or sound with simple
combinations of instruments our brain is
able to analyze this combined wave form
and pick out individual instruments
however when many instruments are
combined only a trained ear would be
able to determine all the instruments
used to create the music because the
combined new wave form is so dissimilar
to the individual instruments
furthermore for us to record and
playback the sound of Beethoven's Ninth
Symphony we would just need to convert
the pressure waveform in the concert
hall into something like the movement of
a needle this is the core concept behind
vinyl records a device measures the
force or pressure levels from the air
particles in a concert hall or recording
studio and graphs them into the grooves
on a vinyl record you can see how the
shape of the grooves closely resembles
the waveforms we have been talking about
to play this record a needle just needs
to follow the recorded grooves and
convert this motion into the motion of a
diaphragm which applies a force to the
air particles thereby reproducing the
original sound thanks for joining us and
learning about sound if you have any
further questions post them in the
comments below subscribe like and tell
your friends and family about something
you learned this episode is about
understanding what sound waves are
branches from this episode are how do
sound waves travel understanding
pressure how ears work how a microphone
and speaker work understanding air
frequency and amplitude loudness and
intensity and understanding wind
movement vs. sound
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thanks for watching and until next time
consider the conceptual simplicity yet
structural complexity in the world
around us
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