Sound: Crash Course Physics #18 

We made quiz questions to help you review the content in this episode! Find them on the free Crash Course App! Download it here for Apple Devices: apple.co/3d4eyZo Download it here for Android Devices: bit.ly/3TW06aP

Dr. Somara has some of the most intense eyes I've seen yet. I feel like she could stare down a goldfish and win.

at 6:39 is where I have to see myself out of the door thank you

My friends and I were walking through a high end bank looking for a bathroom when we were all in high school and when we reached the third floor, it sounded like a fire alarm was going off. We were looking around and none of the employees or customers were reacting in the slightest, and just kept going on with business. Thinking something was wrong, we left. Looking back, all of the employees and customers were 45-60 years old. After watching this video, I realize it was probably one of those security systems you were talking about, because the sound wasn't particularly urgent, but it was really high pitched. More than anything else, I'm kinda pissed that it worked. They got us to leave, bladders full, under the cloak of confusion at the sound. I feel so played.

Sound is a form of energy that produces sensation of hearing in our ears. Sound is produced when a body vibrates. Sound needs a medium to travel. It cannot travel in vacuum. Sound travels faster in solid medium (like wood) as compared to water and air. All musical instruments have vibrating parts/which produce sound. In human beings, sound is produced by the voice box or the larynx. We hear through the vibration of our eardrum, whenever sound reaches our ears. The number of oscillations per second is called the frequency of oscillation (f) and is expressed in hertz (Hz). A frquency of 1 Hz is one oscillation per second. The time needed to complete one oscillation is called time period (T). Hence, the number of oscillations per unit time is the frequency of wave f = 1 /T. The maximum displacement of the wave crest from the central position on either side is called its amplitude. We differentiate sounds on the basis of their amplitudes and frequencies. A human being can hear sound waves within a range of 20 Hz to 20,000 Hz. Some animals like dogs can hear sounds higher than 20,000 Hz. The larger the amplitude of vibration, the louder is the sound. Loudness of sound is proportional to the square of the amplitude of the vibration producing the sound. The loudness is expressed in a unit called decibel (dB). Shrillness or the pitch of a sound depends upon its frequency. Higher the frequency, higher is the pitch and vice-versa. Unwanted, unpleasant sound is noise. Loud noise produces noise pollution, which is harmful and may cause hearing impairment. The velocity of sound in air is approx.330ms−1 under standard temperature and pressure conditions. It varies with temperature, pressure, humidity and density of medium.

This is such a sound video

5:06 gosh, I served in US air base where air planes and fighter jets frequently take off and land. That really did drive me round the bend. Miraculously, I managed to retain my hearing. Cheers for the instructive lecture and reminding me of that memory mate!

One thing I missed in this episode is that even though we cannot hear sounds outside of our hearing spectrum, it doesn´t mean that they have no effect on us.

4:05 did anyone realise the dogs brown patch shifts from right to left on his face ?

Ah this was so good! I need to know the physics of something before I can understand it, so this helped my sound production studies so much. Thank you!

When she was on the doppler effect part an ambulance went by my open window. lol perfect timing.

Thank you for providing the information! Even if this video is 6 years old it still helps a lot! Thanks.

first timer here. Your class is amazing! Thanks for being so clear.

Her voice is angelic.

I'm teaching an introductory music technology course at university this fall. This is my saving grace for not having to dive into the physics!! This came out at the perfect moment in time.

I love how passionate she is! Love the videos 👍🏼

I love crash course but I wish you'd guys would sloooow down a little itty bit, sometimes you guys (and gals) spew out information so fast it takes two times through for me to really soak it all in. I love this course though, thank you guys!

the whole of my words can t even express how much i love this channel and how it helps me

It's useful to describe sound waves as pressure waves, because we can build devices that detect those changes in pressure. I love CrashCourse Subscribed!

someone get this channel nominated for nobel prize awards

"It happens with light, too... but more on that much later" Aw man, but relativistic mechanics are my favorite! :(

Now I know more about sound energy and what it dose thank you I am your #1 fan

It's really quite fascinating to realize that the correlation between music & mathematics is literally off the charts. I didn't learn how to read music (other than strumming chords on a guitar) until I was almost 50... Or so I thought!! I really did try my best... well, actually what I thought was my best, to learn how to play musical notes on the guitar when I was in middle school as well. Honestly, I don't know if this is true for everyone but I was super surprised at what it took for me to understand fairly basic all-around music theory. What it took for things to click for me was to 1st apply it on a piano rather than a guitar. And to go even one stepfurther, if someone would have told me right off the bat how music theory is so dependant mathematics to the point of being inseperable, I would have looked at it from a completely different perspective. BUT in as much as I know this to be soooo completely true/irrefreputable, it's still really hard to wrap my head around the very idea that such a creative artform such as music depends so heavily on something as technical as mathematics. I guess that subconsciouly, I always felt like I had to hide one side of my brain or the other because having two dominant sides ofthe brain is an oxymoron 🤷 ✌️💞✌️

Thank you so much! These videos are even better when I'm just curious about certain things

This is the dopest educational show in the history of the world

7:21 me when I stub my toe

like tbh this is the best of all the crash courses she is an amazing teacher and even the graphics and intro are 1000 times better

human beings are amazing. i started looking up physics stuff because of a psychedelic experience in which i learned how particles and waves work, and now i see that everything i saw was just science. interesting stuff

have a hard time sleeping? put the decibel equation part on loop. it'll put u right out

That ambulance was moving down the street at nearly Mach 1, passing someone at that speed would produce a more interesting effect than a pitch change. Just kidding, great series, good visualization.

The best sounding video ever

Finally after several useless high view videos, I clearly understood the definition of decibel! Thanks a lot for great explanation

Wooow such a great video, I love this chanel!

I'm going to start my sound engineering degree next month such an interesting topic.. as a musician it fascinates me, I think i'll be having fun. thank you for this video very well explained thank you =)

I like the human being hosting this. She is good human.

Excellent video 😃 hopefully I can pass this final tomorrow

Did I just see when Ethan from H3H3 during to rock scene?!

Incredibly smart, incredibly gorgeous and love the accent also! Thank you! X10 to the 25! #belle : )

That unsolved Rubik’s cube is making me sad I just wanna get in there solve it and tell them to leave it alone

@6:50 the number of which you need to take the log is not "a trillion Watt per metre-square". it has no dimension since you divided a quantity by another quantity of the same dimension or unit. So it's just "a trillion", period. This why (deci)bels are so confusing: to compute them, you need to take some reference point (noted I_0 in the video); this is why there are actually several (and possibly, infinitely many) decibel scales depending on the reference chosen for a particular application. Oh, and there actually is an absolute maximum to that scale: when the sound wave becomes so intense that the depressed phase of the wave basically becomes a vacuum or "cavitates".

First video on this channel, and I did not expect at all to see Ethan down here! Really useful video btw papa bless.

Great video, thank you very much ❤

This is a good video to teach deaf people how sound works, even if they can't hear them. Thanks!

4:48 Was this a reference to H3H3s EDM concert video

this channel is the best on youtube.....

First video ever I had to slow down

Sounds great😂thank you for the lesson

Descpribing sound as pressure waves makes sense why a jet flying in supersonic speeds near buildings will do some serious damage. Since it creates a difference in pressure in the air.

Wait, measure the distance of stars? I would say the relative speed the star is moving to earth. Also I highly recommend that everybody build at least one set of hifi speakers, measuring the impedance and characteristics, running simulations, applying Thiele/Small theory in the design of passive crossovers. I learned a lot by doing that three years ago just for fun. Buying a calibrated microphone is not that expensive and a nice DIY project can be made, learning A LOT about sound. Hmm. Now that I think of it, I forgot most of it. :-)

Omg you added Ethan!!!!!

As far as sound this takes effect. Light can measure distance in the universe. There is a difference. Sound can travel very far but can be blocked at anytime therefore cannot be used as measure instrument. But this great vid and great information.

Episode 24 "Light" confirmed.... damn, still have to wait so long...

Crash course on music theory please :)

My eyes glaze over when the math starts LOL

Incredibly informative! It's okay to be smart. :)

Hey Crash Course, I really like this channel. The diversity of topics and depth of insight is something that is, in my opinion, unrivaled by most other RU-vid channels. The idea of this channel alone, that being videos of moderate length explaining a range of topics in detail, is priceless. Now more than ever it is vitally important to the American economy that our citizens be intellectually literate, especially in fields such as science and technology. Come to think of it, it may be a good idea for you guys to make a STEM (Science, Technology, Engineering, and Mathematics) playlist. Just a thought. On another note, what would you guys/girls (meaning whoever is reading this) of an interview series on Crash Course? It would be really interesting to see Crash Course collaborate with scientists, artists, authors, poets... etc. Couple that with longer interviews with the guest and I think it would have the potential to really grow the channel and even further diversify the content, appealing to a different breed of knowledge junkie. I can only hope that some high profile names in the various fields of expertise would be willing to collaborate. Richard Dawkins for biology, Lawrence Krauss for particle physics, Bill Nye for climate change and engineering, Cornell West for social and political reformation and history, and so on and so forth. I believe that and do of those names have collaborated with the channel Big Think (which is another channel that I love), and they have only have about 1/3rd of the amount of subscribers that Crash Course has. Not to mention their connection to PBS, which may hold some sway. I believe that Crash Course is connected to a few other large channels as well, like SciShow, which could also host those sort of interviews and collaborations.

Dear, Crash Course, I am wondering what is the name of the song they used for the H3 Ethan reference. I want to get that sound file for my mp3 player. It sounds nice even in this episode. Keep up the wonderful work crash course.

This is just what I nees to speed up my understanding before getting into the math used to describe the physics, btw nice Feynman books I have the spanish-english version, really nice book (I'm a native spanish speaker)

Thanks Dr. Somara!

It’s been a while since I’ve been following your videos, and I must say, they are amazing! By any chance, is there a scope for business collaboration?

I wish there was a crash course music! But, this is definitely a start 😊

I love your videos, but why don't you make them a third longer while reducing your talking speed by one third?

Wow, PoGo Fever has even infected Crash Course!

Eardrum in our ear is also called tympanum

That Pikachu while describing about picowatts was amazing.

4:50 I see you put h3h3 in there...

Talk about standing waves!

Now, I think I have a good idea. Since energy is Force times the distance the force is applied. Think of a pulse. You oscilate once which means you apply a force up and down on a rope. The part of the rope you pulled up and then pulled down. You only pulled down on that part of the rope. That part of the rope pulls down on the next part of the rope just as the part you pulled down goes down. And then it continually is replaced. (i.e think of a wave at a stadium. The people to your left moving up pulled you up and then as they went down their movement pulled you down as well as you pull down the people to your right.)

Thank you

thank god for this channel

what is difference between Isolation and Separation in Biophysics??? n pls upload vdo on electrophoresis.

Objection! The apparent frequency is changing as the source moves. Meaning the perception that the pitch is changing is false, its the amplitude that is changing

Interesting. Simple and compact infos

I love her videos!!

crash course music theory for the love of jebus

Great birthday present! :D

do a video on ultrasound! specifically diagnostic medical sonography

Looking forward to next week :-)

Thanks for this channel!

There should be a CrashCourse section on Linguistics :'( Greetings from Chile, South America.

*_Awesome crashcourse keep creating such crucial videos_*

First time I discovered the Doppler effect? DooM I and running forwards, or backwards with a rocket launcher, as a kid :D

Dear crash course can you guide how these fantastic animations are designed?

Waw , this was amazing ✨

love this channel!

Why sound waves traveling in all directions ?? Recently I've read about sound wave propagation. Let's look on loudspeaker. If it creates sound waves by pushing and pulling the air in front of it , how we can hear sound when we are behind the loudspeaker or above or under?

watching this to help me do my uni HW haha

Love crash course

I like your Lego figure of the James Webb Space Telescope. DFTBA ! :)

Omg the h3 reference

This was really fun to learn !

Pokemon Go!!! Walk on the street and sticking your eyes on the Phone playing Pokemon Go and there you go, "Crash" course XD. And Ash Ketchum's cap in the Doppler effect too XD

great video

In Science we were learning about Sound vs Light. I may know what's the difference to them or what's similar to them. I'll tell ya something. What I know is sound can go through any sort of objects that are opaque. Light shines through any object that are transparent or translucent. Ive learned it since in high school and even I'm in Year 7

This is such a sound video.

hello, crash course people, please make a video on spring constants and if we change the spring lenght what happens to its constant??

thanks very useful

Nice

please show us something about free electricity?PLEASE!!!!!!!

Just trying to make my room soundproof so I can have some fun if you know what I mean