8.01x - Lect 31 - Forced Oscillations, Normal Modes, Resonances, Musical Instruments
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- Опубліковано 27 сер 2024
- This Lecture is a MUST. Forced Oscillations - Resonance Frequencies - Musical Instruments - Break Glass with Sound - Great Demos.
Assignments Lecture 30, 31 and 32: freepdfhosting....
Solutions Lecture 30, 31 and 32: freepdfhosting....
Watching Professor Lewin's lectures makes me happy. :') Such a beautiful way of teaching.
You deserve some special award for this lecture. Hats off👌👌
I feel being in emotional resonance with your way of teaching.. love and respect 💙
One of the best lectures! (8.01x - Lect 31 - Forced Oscillations, Normal Modes, Resonances, Musical Instruments)!
Dear Prof. W. Lewin. I wish one of the first lessons on music I was taught would have been this way. Now, long time ago, I find extremely interesting the fundamentals on pitches and harmonics, but what it is way more fascinating: we, musicians, are used to work with that matter, the so called pitches, which are nothing but resonaces. Now for a while I have been writing music and considering the sound experience beyond that pitches, which is naively called 'noise' or 'sound 'saturation' (the latter for those who are for it), that is to say: THE TRAVEL from resonance to resonance that experiences sound. I really appreciate that crystal clear lecture (and the elegant maths beyond, which I studyied when I was young, or younger) and the feeling that I can rely on my intuiton regarding sound nature when it comes to inventing music. Kind regards.
thank you for your kind words
I was really terrified at the end when you touched your forehead after helium demo. what an honest man you could ask someone else to do it thanks for your effort sir
Professor, when I fill a bottle with water, as the water stream hits the surface it produces a sound. And as the bottle gets filled, the sound (tone) changes along with it. Is it because the length available for the sound waves to travel gets shorter and thus the frequency increases?
yes
Excellent explanation, by far, the best teacher I have ever seen.
Greetings from Argentina!!
25:30 Now I understand why speed of sound at room temperature is equal to 4nL in resonance tube experiment. We had used tuning fork which has two nodes and substituting that in above equation gives speed of sound 4nL. My school teacher failed to explain it to me. But you (in 1999) didn't. Thank you, professor.
You deserve a noble prize for teaching physics ,This was awesome LITERALLY!!!!!
:)
You played that song like a pro!! I'm a musician..I would know;)
@29:00, I saw a magician.
Finally comprehended resonance.
Thank you very much Sir....
you are very welcome!
47:50 😂😂😂 That was amazing!!
I'm a student of class 12 from India professor
U r super awesome professor
I wish your name remains immortal in the world of physics
U r my role model professor
And I wish to be like u professor
This video won my heart thank u professor
Thanks for your kind words
Wow
Walter Lewin replied to me that's cool 😁
This is my favorite of 801
best teacher in the world
Very Beautiful Lecture, though one thing left me very intrigued. The wind pipe experiment, where you rotate it. You said that it picked out different Harmonics, higher frequency ones and lower frequency ones, you also said that the harmonic frequency can be found linearly, F1 being 480, so F2 would be 960, F3 1440, and so on. I played the frequency along the guitar (Turning my would be A=440 to as close as 480) and what I found was while it hit 480 and 960 it also hit in between sounds, considering A as 480, your pipe also hit C# and E respectively. I wonder why that would be if the harmonic and frequency are based linearly, what am I missing? ( I have tested it by playing my guitar as you rotated the pipe, which is where I found the C# and E notes).
PS: By the way, those (C# and E) are in music referred to Third and Fifth notes in the A major( Diatonic scale), combining the First Third and Fifth notes are what are usually referred to Major Chords. Is this related to how harmonic works? Still trying to figure out how it relates to the linearity of harmonic, as the third and fifth are not linear to any Nth degree with the First.
Thank you. By the way I found out years later that what I believed at the time was the fundamental was in fact the first harmonic. Had I measured the frequency then I would have seen it.
It would be great if you came out of retirement and went back to teaching at MIT. 🙏👏
I taught 43 years at MIT. I am now 82.9 yr old. I think I deserve my retirement.
@@lecturesbywalterlewin.they9259 you do and your videos will continue to educate the future generations.
@@lecturesbywalterlewin.they9259 43 years is a long time
Dr. Lewin, why do you use helium instead of hydrogen for the last demo?
+Ex Zee helium cannot burn - it's safer.
Sir i am doing same with my glass but doesn't get the sound
Professor why is it that I hear the loudest sound from a body when it is at its resonating frequency ?
Isn't it that only the amplitude is maximum in its resonating frequency and it is not in its maximum frequency
Then how come I hear the loudest sound ?
it's becoz at resonance freq the amplitudes are the highest
Professor does it mean that louder the sound greater the amplitude ?
Why doesn't loudness of sound depend on frequency ?
Lectures by Walter Lewin. They will make you ♥ Physics.
1 second ago
The frequency plays a role as our hearing sensitivity is frequency dependent. People's audiograms are very different. Old people often lose sensitivity above 3000 Hz. I can not hear 5000 Hz anymore.
Thank u professor
Professor, I understand that natural frequency is the frequency of the oscillator in the absence of damping. For example, when there is no damping and swing is kicked, the swing would oscillate at its natural frequency. My question is: Why is that kick of the swing is not included/accounted in the differential equation describing the system?
Initial conditions can be included to yield the complete solution in time. You will then find the transient solution and the steady state solution. The transient dies out becoz of damping. The steady state will be the resonance freq. Watch my 8.03 lectures in which I cover this. If you kick an oscillator without damping it will oscillate in a superposition of available resonance freqs.
Lectures by Walter Lewin. They will make you ♥ Physics. Thanks professor. I will watch and then ask you my question if I don't understand.
In the case of standing waves in a string, you can Fourier analyze the kick and find the various amplitudes of the various resonance frequencies - that's what happened with violin, piano and guitar strings. I do cover that in my 8.03 lectures.
Lectures by Walter Lewin. They will make you ♥ Physics.
Now, I think I understand. I was actually thinking of using the impulse function. But, didn't realize impulse functions has wide spectrum of frequencies, which could Fourier analysed.
Thank you for your reply, Professor.
I love how you describe resonance as the system going BERSERK
I'm glad!
i was listening to the lecture with earphones and the time he said that frequency will be much higher that you will need to close your ear i was like thankyou sir . but can't listen at this moment because my father is sleeping next in the room.but want to watch it at higher volume.
sir you drew graph between amplitude and frequency for three coupled oscillator. in that amplitude for all three natural frequency were drawn different. how is this possible? is damping differ at different natural frequencies or is it due to fact that amplitude of force applied are different and when its kept same amplitude of different natural frequency will become similar?
watch all my 8.03 lectures on coupled oscillators. If you then have questions I'll be happy to answer them. Always refer to the lecture and how many minutes into the lecture. If there were 3 normal modes, then there must have been 3 coupled oscillators. I probably showed the curves of the steady state solutions of driven oscillators. Amplitudes of the 3 normal modes are always different.
thank you sir
Professor, I have another question. Are natural frequency and resonant frequency the same?
My understanding is resonant frequency is the frequency of the input that results in maximum gain, which need not necessarily be same as natural frequency. ( I guess depends on the terms taken for friction)
Here, at 68:40
m.ua-cam.com/video/j1ADxLi1wYg/v-deo.html&mode=NORMAL
Professor Wit Buzsa shows that peak value occurs at a slightly lower frequency than the natural frequency. So, I think resonant frequency and natural frequency need not be the same.
Am I correct? Appreciate any reply.
>>>My understanding is resonant frequency is the frequency of the input that results in maximum gain, >>>
maximum amplitude is *NOT at the resonant freq but it's below the resonance freq.* ua-cam.com/video/Y_DmzZcQR7A/v-deo.html
Lectures by Walter Lewin. They will make you ♥ Physics. Thanks a lot, professor. I plan to watch 6.03.
does spring mass oscillation produce standing wave
does it same goes with coupled oscillator?
I always don’t understand when the system resonants, where does the energy come from? “Small input, large output”. Wouldn’t that violate the conservative of mechanical energy?
no violation - of course energy is conserved. When there is resonance the small displacements have there maxima at the very same time. Thus the final amplitude is HUGE
@@lecturesbywalterlewin.they9259
Thanks for the prompt reply! Professor. Do you mean the energy distribution is not uniform? Thus at some locations energy is small (small displacement), and at others energy is large (large displacement).
@@lecturesbywalterlewin.they9259
Consider a spring mass system. We can keep the same input force magnitude and gradually increase the input frequency. When it resonates, the displacement of the mass, thus speed, thus kinetic energy, is large. After it passes the resonant frequency, even though the force is the same and the frequency are larger, the displacement of the response, thus the speed, thus the kinetic energy, becomes small. There must be something wrong in this reasoning, but I can't see where.
Sir I'm not quite understand why string vibration being like infinite coupled oscillators.....
how about for standing wave of string?
After long practice i find it almost difficult to form standing wave on a general rope(as it goes more circular rotation than transverse displacement), then i just watched your rope it's helical in shape so my question is where to find it?
and it's been honor and very grateful of you that you provide us with such great lectures.
But now do something more give us links also where to buy these small-small scientific equipment's you use.
right now just help me how to make a standing wave easily?
and if slinky rope is required where to find it?
+Arvind Sharma send email to Andy Neil (aneely@MIT.EDU) he may be able to help you. He is in change of the physics demos at MIT.
+Lectures by Walter Lewin. They will make you ♥ Physics. Thank you sir you initially gave me a reference of other guy at mit but he didn't reply my email....
+Arvind Sharma Not all Professors at MIT answer Physics Questions.
Bestestttt lecture 👏❤
is the amplitude during resonance is more or equal than during its natural frequency professor?
a resonance frequency is a normal frequency. Different names for the same
Lectures by Walter Lewin. They will make you ♥ Physics. thank you
32:42 my exact face when I watch this lecture 😀
same
Hello super profesor !!!! , so if we kept our hand or any mucle from a fixed piont and we tuned our mucle could we have weightfree excersize maby in astronauts or mabe in people that are abed .
Why does professor take Fo(coswt)?why not Fo(sinwt)
The reason is that he was in love during his highschool days with a girl whose name was Cosje
Professor what will be the effective length if Only the first hole is covered at 29:30 ?
the effective length is the distance to the first opening. However if the opening id very small, it's more complicated.
So professor even if the second hole is kept open, nothing different will happen? the effect length will still be to the first hole and the second hole is sort of ignored ,is that right professor ?
yes, that is correct for my model, but with real flutes it's different; it depends on the size of the openings.
Thank you for answering my questions professor ,Good day :)
Amazing...
Amazing
Love you sir g
The ending was very 🎭🎭🎭 funny....
......
Sir, after hearing the bridge example, I just can't help but imagine a bizarre consequence of resonance, where any object could go berserk when resonance frequency is met by a wind source or anything. How is it managed in daily life sir? Do the objects have good damping?
Sorry, if it's a silly doubt sir !!
Engineers have learned from, the mistakes made in the past. This will no happen again.
@@lecturesbywalterlewin.they9259 Thanks a lot for the reply sir
@@lecturesbywalterlewin.they9259hello Sir I am big fan you ❤
@@lecturesbywalterlewin.they9259Sir I Have A Question
47:50 Donald Duck???
The title reads like a little poem😊
48:00 An old man nearly suffocates and they just smile and gather up their things :)
ha ha ha I was not yet old then !!!! 1999
9:16
Stop Focus on iron man no matter how smart he is in building his own technology far ahead of time,The brain of Walter Lewin had clearly surpassed iron man even though he teaches physics rather than inventing something
How to purchase your book For the Love of Physics
I want to read can u help me professor I'm a high school student