8.03 - Lect 9 - Sound Cavities, Resonance Frequencies, Musical Instruments

[@meetghelani5222]

Professor Lewin's and feynman's lectures better than netflix or anything out there to binge watch for a person interested in science!

[@fernandosoler3005]

QUE PRIVILEGIO TIENEN DE APRENDER CON UN PROFESOR TAN SABIO Y ALTAMENTE PREPARADO Y LA FORMA DE ABORDAR, LOS ASPECTOS DE UNA MANERA TAN VARIADA Y AMENA, QUE BUENO....

[@PauloConstantino167]

You inspired me to build a small string instrument with 4 strings. I put it on my table and it sounds so loud! What I shame I was born in a different country and couldn't go to MIT when you were teaching there. But how lucky we are today with the internet, so I can watch you not only once at an MIT class, but as many times as I want by pressing rewind and rewinding Walter Lewin :)

[@lecturesbywalterlewin.they9259]

😊

[@raghavsh8560]

True As a child it was my dream to go to MIT and study undergrad with professors like Prof. Lewin, but I guess I’ll go there for my post grad ;)

[@studyonly4979]

I am actually preparing for IIT JEE i was not getting the feel of resonating sound waves in organ pipes.... its just amazing lec... i enjoyed it so much... thanks for the quality ❤❤❤❤

[@marcopilati7464]

I want to say again, better: great, great, enormously great Teacher! Congrats.

[@lecturesbywalterlewin.they9259]

:)

[@sunyue1909]

At 22:25 the list works only for the fundamental mode i.e. n = 1. I was confused for a while. In general, the ratio of the wave length of the open-open case to the one of the closed-open case is (2n-1):2n. It was a great lecture! Thank you, Prof. Lewin!

[@mufaddaltinwala5902]

8.01 and 8.03 by you has opened up a new door of understanding the nature and physics...Am revisiting my engineering concepts through your lectures on vibrations.. Great:)

[@georgH]

The 7th harmonic is suppressed in pianos because it's the first one that causes a dissonance when the others are also present. The 8th harmonic is fine and the 9th clashes again but it's too faint to be perceived or have any effect. See this wikipedia image: en.wikipedia.org/wiki/Harmonic_series_(music)#/media/File:Harmonic_Series.png

[@lecturesbywalterlewin.they9259]

:)

[@gulzarali6370]

Your lectures are mesmerizing 😍

[@lecturesbywalterlewin.they9259]

Glad you think so!

[@AmanNarwarVlogs]

Nice Explaination sir, I am watching this lecture for JEE 2025

[@lecturesbywalterlewin.they9259]

Keep watching

[@edwarddocherty6576]

What a brilliant lecture this was. Must be one of your favourites ?

[@sanjoykumarrouth6410]

Best teaching in the world.

[@lecturesbywalterlewin.they9259]

:)

[@jiteshkumarsahoo2830]

Thank you sir for these wonderful lectures!!!

[@aeroscience9834]

At 32:39 when you went from the fundamental to the second harmonic, it sounds like a fifth, but it should be an octave. I think what you thought was the fundamental (the lowest pitch you got) was actually the second harmonic.

[@aeroscience9834]

Also I measured with tuner and got the lowest frequency at about 420 Hz

[@aeroscience9834]

So it was definitely the second harmonic, not the fundamenta

[@lecturesbywalterlewin.they9259]

I agree that what I thought was the fundamental was actually the 2nd harmonic. Several people have pointed this out to me.

[@aeroscience9834]

Lectures by Walter Lewin. They will make you ♥ Physics. Ah ok. Thanks for the reply

[@sihanchen1331]

33:45 Artist

[@kartickchandramanna267]

Great Physics Teacher l never seen!

[@lecturesbywalterlewin.they9259]

:)

[@mohakjani6220]

In India v have a instruments which is very similar to what u r daughter made it is called aktari which literally means one string and as usual great lecture thank u

[@vishalkurmi6323]

You are very very very very very good teacher love you sir

[@atharvsakhala9469]

this lecture is so much fun!!!! wish i was there :)

[@diwashkarki9761]

How can I calculate the frequency produced by counch shell? Have u ever played that.??

[@ShwetankT]

Do you have any idea about the whole 432 versus 440 standard tuning controversy? Seems bollocks to me. By the way, it is amazing that successive octaves are exponential quantitatively while they sound linear to our ears. Awesome videos. Thanks.

[@lecturesbywalterlewin.they9259]

en.wikipedia.org/wiki/Musical_tuning

[@aeroscience9834]

31:06 that was not an octave, it was closer to a seventh.

[@aeroscience9834]

I guess that flute isn’t well modeled by a narrow tube!

[@seanki98]

Excellent lecture as always, professor. Was wondering if it should be 2L in the denominator like you said... 4L is written for some reason for the equation of k_n at 56:38

[@lecturesbywalterlewin.they9259]

what I have is correct

[@sunyue1909]

In this lecture Prof. Lewin said 2L but wrote 4L down. I believe what he said😁

[@hardaatsinghbaath7475]

sir, could you suggest some ways in which I can satisfy my curiosity for physics? it's a pity that u were at mit about 20 years earlier :)

[@abducted3062]

Love for professor Walter lewin.

[@adamlantos2319]

Also, why do we hear sound coming out of the pipe with two closed ends? Is it because the pipe also vibrates with the same frequency as the air inside it? IF so, if we strike the same frequency for an open-closed pipe as for the closed-closed pipe, then the sound intensity of which is higher and why?

[@marcopilati7464]

Great teacher!!

[@victorpaesplinio2865]

The best thing is that I'm watching this on Christmas Eve. That was a nice try playing jingle bells hahaha And the students are really talented Thank you very much for these lectures. They helped me so much on my exams and motivated me to keep studying this quarantine! And if you read this before 2020 ends, happy holidays to you!

[@alistiqamat7066]

أحسنت الإختيار تحياتى الحارة ............

[@sandrocavali9810]

Absolutely excellent

[@sathishr7774]

why diameter is not present in calculation of resonant frequency of pipe. if i use a large dia flute will i get same resonant frequency. thanks

[@lecturesbywalterlewin.they9259]

as lo;ng as the dia is much smaller than the length you can predict to a fair degree of accuracy the resonance frequences.

[@adamlantos2319]

I have a question regarding the professor's daughter's musical instrument. I don't understand how the transverse wave from the string gets converted into longitudinal wave at the base of the "KFC tin". Same question applies to the fork tuner. Say the fork tuner oscillates in the x direction. Then why does It create an oscillation of the table in the y direction?

[@lecturesbywalterlewin.they9259]

+adam lands My daughter Pauline played the violin The string is coupled to a box. The box (not the air in the box) vibrates and that produces pressure waves. Remember the demo I do with the music box. You cannot hear the sound of the vibrating small prongs UNLESS you place the music box on a surface (e.g. the table). The table cover starts to vibrate and it produces pressure waves strong enough so that you can hear the music box play. This is NOT a violation of energy. The box enlarges the surface that vibrates without any "gain" in energy. Take a tuning fork and bang it. It's very hard to hear it. Now make contact between one end of the tuning fork with a table or box and you can now hear the tone very well.That's the same idea. I did that demo!

[@adamlantos2319]

Professor, I understand those demos that you explained. What I can not understand is this : In the tuning fork demo(with the table), the fork vibrates horizontally. Then it gives that energy to the table and then the table vibrates, but it vibrates in the vertical direction(because it produces pressure waves that are longitudinal). How does the transverse wave on the fork gets converted to longitudinal vibrations of the table?

[@sunyue1909]

At 55:11 I wonder if the systeme is close-close, because in an open-open system its fn is half of the one of the close-open system.

[@lecturesbywalterlewin.they9259]

you are mistaken

[@sunyue1909]

Thank you, Prof. Lewin! I understand it now. The pressure at both open side is zero, like the displacement at the both fixed side of a string.@@lecturesbywalterlewin.they9259

[@tushardey7653]

Sir you are genius

[@marcovillalobos5177]

I thought that membranes oscillate in a kind of bessel function, but you wrote it down a sinusoidal one to describe its movement

[@lecturesbywalterlewin.they9259]

use google

[@marcovillalobos5177]

@@lecturesbywalterlewin.they9259 Partial differential equations are a little bit out of the scope here

[@bilalhussein9730]

@@lecturesbywalterlewin.they9259 Professor Lewin you might be interested to know that Ritz solved for the modes of Chladni's plate (by hand)! in 1909 and the solution fits in a small Mathematica program seen here: i.stack.imgur.com/iy8Cl.png.

[@namesurn8590]

so tuning fork oscillates parallel to board. we hear it because of reflections from walls? (wall is not really perpendicular i think)

[@lecturesbywalterlewin.they9259]

we hear it becoz of the sounding board. I show this with a demo

[@gglee8831]

I have a question about standing wave in the wind instruments. I can understand the standing waves of the string instruments can produce the sound. However, the standing wave trapped in the wind instrument can be heard to human?

[@lecturesbywalterlewin.they9259]

A wind instrument must be open at one end. Sound is a pressure wave. The pressure fluctuations at the open end propagate in the room and reach your ear.

[@chaitanyakasani7718]

why are the tuning forks in u-shape? why not just a rectangular block?

[@babuj6949]

As you said in previous lecture, reflection is zero at the junction of two mediums which have same mue and velocity. open-open sound cavity satisfying this condition at its both ends, so there should nt be reflection at the ends. then how standing wave can form in open-open sound instrument?

[@lecturesbywalterlewin.they9259]

>>>>As you said in previous lecture, reflection is zero at the junction of two mediums which have same mue and velocity.>>> **** yes that is correct if you take this in context. Attach a rope to another identical rope, generate a wave at one end. The junction is "invisible" as it is a continuation of the "same" rope. >>>>open-open sound cavity satisfying this condition at its both ends>> Yes, you have a good point. However the boundary conditions of the "world" outside the cavity are different. Inside the cavity sound is confined to the cavity, outside it is not.

[@babuj6949]

Thank you sir for your reply. so, sound feels a boundary between confined area and unconfined area even though mue (velocity) is same. sir, can you give some reference for this to understand mathematically?.

[@babuj6949]

and another point is that sound cavity frequencies only depend on length of the cavity, not on the material of the cavity. so any kind of material can be used to create same kind of resonant frequencies for fixed L?

[@ssys5559]

I think maybe mue is going to be different at the boundary due to the compression of air into the anti node?

[@AryanKohli-hkscx]

49:38 this looks like a scene from a horror movie🤣

[@marcovillalobos5177]

Why does the faster you spin the tube the higher the pitch gets, you didn't change the length of the tube and the velocity of sound didn't change either!

[@lecturesbywalterlewin.they9259]

good question, use google

[@forumforum9128]

43:40 nice song. :) Does anyone know its name?

[@chessematics]

8:00 is that "Für Elise"?

[@josephanderson7237]

Rag Time Annie on the violin?

[@chaitanyakasani7718]

why are the tuning forks in u-shape? why not just a rectangular block?

[@lecturesbywalterlewin.they9259]

What would be the size of these blocks and what metal would they have to be made of to cover the range from 100 Hz to 6000 Hz? That is the range that is covered by tuning forks. And what would be the decay time of the sound?

[@namesurn8590]

at 31:30. why it must be corregated? why if twirl faster we get higher harmonics?

[@lecturesbywalterlewin.they9259]

good questions. Higher speed higher freq is easy to understand - the corrugation is not so easy - use google

[@chainarongtae]

It frequency depend on ....? Thanks you

[@prestigious786]

I have a question, "At 28:29, why was there loud sound when you put tuning fork on a student's head?"

[@lecturesbywalterlewin.they9259]

brain resonance

[@prestigious786]

@@lecturesbywalterlewin.they9259 why wasn't there any sound when you put tuning fork on your own head? Was that a trick?

[@lecturesbywalterlewin.they9259]

@@prestigious786 my head is filled with brains, in the absence of brains you hear the resonance of the hollow skull

[@usmanmuneer6143]

@@lecturesbywalterlewin.they9259 Yes, that was a really good joke but it was a trick after all right?

[@dogscats8141]

Bravo!!!!!!!!

[@sanjoykumarrouth6410]

Great teaching

[@lecturesbywalterlewin.they9259]

:)

[@chaitanyakasani7718]

In a quartz wrist watch, if i supply the dc battery voltage lets take 1.5 volts) across the piezo electric quartz crystal just for 1 second, so how many vibrations is it capable to make?". is there any mathematical equation for this ?

[@lecturesbywalterlewin.they9259]

If you apply your 1.5 V battery the quartz will not start to oscillate. Use Google.

[@chaitanyakasani7718]

but the voltage ratings of wrist watches batteries are generally around 1.5V

[@lecturesbywalterlewin.they9259]

yes, but the battery on its own will not make the quartz oscillate. It's an electronic circuit that makes it oscillate and the battery drives that circuit.

[@chaitanyakasani7718]

Well, ok . Even then my question remains the same. If i supply a 1.5v signal across the electronic circuit (electronic circuit is further connected to quartz crystal) just for 1 second. How many oscillations can this quartz crystal make?

[@lecturesbywalterlewin.they9259]

It depends on the thickness of the crystal. en.wikipedia.org/wiki/Crystal_oscillator

[@admiralhyperspace0015]

I love the internet.

[@AlcvinRyuzenRamos]

Great teacher!!!!! ;-)

[@er.agnihotri9955]

Sir will u teach me online plzzzzzz

[@habenbelai7420]

1:07:21 The shape looks like that of a Bowtie

[@sabrewolf479]

The gods worship and obey mathematics.

[@SnakeEyesPlayzz]

BUDHE BREAK LELE VESE BHI SAMJ NAHI AATI TERI !!!!