Sir, you are the bēst, i am writing msc thesis on standīng waves and travelling of violin strings, is there anything you can do to help me, i am a very good violin player. my email is firstname.lastname@example.org
Sir, I have a question about standing wave, if wave (when it reflects from the wall) changes its phase for 180 degrees shouldnt then the reflected and the coming wave be out of phase and cancel each other
Prof Lewin, Flute is closed at one end and through the other end, air is blown. How do we hear music? Isn't the wave trapped inside the flute? How does the music escape?
Just one line from you from would suffice. Hope my dumb questions doesn't cause irritation/annoyance. I am just trying to make an analogy with antenna as I've an engineering degree.
The simple mention of the fact that, in the standing wave equation, the spatial and temporal information is not interlinked makes for a great tool for understanding how standing waves aren't being shifted left or right (speaking purely in terms of vertical vs. horizontal displacement).
Excellent explanation of the standing wave professor. Thank you!
Professor WALTER LEWIN are you even human , Physics is a beautiful sound of nature in varying harmonics and you are by all practical purposes the resonating column for it. Sir can you please tell me how you can be so good.
You are a great professor it's just that my input data rate is alot
slower than your output rate. My Input FIFO has overflowed. The great thing with having things on video is that I can watch it over and over until I get it.
After i watched this lecture i downloaded a software oscilloscope(for microphone) and a frequency generator and i am testing various frequency's and harmonics to find nodes and i am sliding with my chair slowly away from the speakers to find nodes ..its really fun when i find a node i feel a drop in pressure..its been 2 hours i have been doing this LOL and not bored at all! thankyou prof. lewin
In case of fundamental frequency, we always get high amplitude as compared to other harmonics so is it safe to say that if we want to have destructive resonance then fundamental frequency is the most suitable option for it?
This will often be true. However, it's in principle possible for objects to break much easier in the second harmonic than in the fundamental. Suppose you took a glass rod of length L which is thinner (thus weaker) near L/4 and 3L/4.. It may then be easier to break it when you excite it in first harmonic above the fundamental than in the fundamental. There may be many objects (including bridges and glass wear) that are more vulnerable at res freq above the fundamental than at the fundamental.
In case of wine glass, there is only one resonance frequency which if a speaker matches with then we get resonance.......
Other objects also like Tacoma bridge also have only one resonance frequency but why strings and woodwind instruments have more than one resonance frequency?
ALL objects (NO exception ) have many resonance freq. That includes wine glasses, bridges, plates of any shape, strings and sound cavities. If you excite them (pluck, strike, bang them, blow air . . .), in general the object will oscillate in a combination of its res freq. All musical instruments do that (I demonstrated several instruments in class). If you drive them with any of their res freq they will start to oscill in ONLY that freq. The bridge was NOT driven at one of its res freq. The reason why it only oscillated in at a low res freq (maybe even the lowest) is that it would have taken more power than was available to also drive at the same time a higher res freq. If you drive the wine glass with a sound freq that is the glasses first harmonic above the fundamental it will start to oscill in that freq but the glass will probably not break as that would require more power than we had. End of story
YOU still miss the point. I cannot help you anymore. I tried to explain this to you more than 3 times referring to my 8.03 lectures. This is my last msg on this topic. ALL answers are in my lectures.and in previous msgs
ALLLLLL objects have many resonance frequencies. If you drive them with one of their res freq they will "react" accordingly, but that does not mean that you can destroy them. Look at my great demo of the many resonance freq of a disc (Chladni plates). I search for the res freq and you see the results !!! Lect https://www.youtube.com/watch?v=GFR8UJK3Mzc&index=1&list=PLyQSN7X0ro218ZADJkvINBhTUAQeDMHf-
It's even more impressive to do this with a square plate https://www.youtube.com/watch?v=Qf0t4qIVWF4
I got this definition of oscillation from web.....
"Resonance can be defined as the condition in which force is applied to an oscillator at the point of maximum amplitude. In this way, the motion of the outside force is perfectly matched to that of the oscillator, making possible a transfer of energy."
How will you explain this?
It depends on your definition. If you call an oscillator the source of the energy (circuit) that causes oscillations, then I am the oscillator as I move the string. It's really irrelevant for me - what counts is that you understand how you can make an object oscillate.
Sir, I m not able to clearly imagine what is the scenario in case of a longitudunal wave like sound??Its a stupid question but it really means a lot in understanding standing/stationary longitudunal waves and its applications in organ pipes.Plz help............
The resonances wavelengths are the easy. If you knew the mass per unit length and the tension, you can then also calculate the speed of propagation and that will allow you then to calculate the resonance frequencies (as you know the resonance wavelengths).
Sir, I guess I may be asking something a bit off topic. But I think you are the best person to answer it.
My question is, when we consider a subatomic particle as a wave, then which parameter of the wave is related to the mass of the particle?
>>>y= asinwt is not travelling at all is it standing wave?>>>
It is not a standing wave. Traveling and standing waves MUST depend BOTH on x and y (and t). y=sin(kx)*cos(wt) is a standing wave. k = 2pi/lambda. It has nodes (y=0) at x=0, lambda/2, lambda, etc.
y=cos(wt-kx) is a traveling wave.
+JunYu Lei If the string is closed at both sides, then at x=0 and at x=L the displacement must always be zero. As long as your solution meets those conditions it does not matter whether you have sin or cos.
If the string is closed at one end but open at x=L, then your solution should give a displacement of 0 at x=0 at all times and dy/dx must be zero at all times. As long as your solution meets those conditions it does not matter whether you have sin or cos.
I have a question about the traveling wave equation y=2sin3(x-6t). When I search on the internet I always find that the equatin is y=2sin(wt-kx). When we write equation for AC voltage it's also u(t)=U*sin(wt + "theta" ). So I'm not sure which one is correct. Please forgive me if I am missing something obvious, thank you in advance.
+Lectures by Walter Lewin. They will make you ♥ Physics. Thank you so much for clearing that up for me and answering so quickly. I see now that I need to study a bit more before asking a question. I would just like to take the opportunity to say that I love your lectures they're so interesting and helpful, Thank you again very much.
+Nikola Vulinovic TRAVELING WAVES
y=2sin3(x-6t) = 2sin(3x-18t). Thus k = 3 (lambda = 2.1m) and omega is 18 rad/sec. y=2sin(wt-kx) => y=-2sin(18t-3x). Again lambda = 2.1 m and omega = 18 rad/sec. The - sign is a phase change of 180 degrees. NO PROBLEM! These are TRAVELING WAVES!
Dr. Lewin, I've watched several of your lectures since the start of my first year in my physics major and I just wanted to take the time today to thank you for all your dedication you put into these lectures. Thank you for your amazing teaching and making me love physics.
I am a professional trombonist. I really enjoyed your presentation. I have a question regarding what I believe to be standing waves. I blow air through my lips, which causes my lips to open and close rapidly. The frequency can change but it gravitates towards the harmonic series related to the length of the trombone at any particular time.
If air is being displaced into the instrument, the air would also be displaced back into my body when the lips recoil back to their original position (which means my lips actually move forwards and backwards as opposed to just 'up and down'- the 'open and closed' is a byproduct of 'back and forth').
If there is also air being displaced into my body, then that would mean my body resonates like a drum.
If my body resonates like a drum, then the amount of tension my body has will change the amount of resonance it can produce. Does this mean that body tension will change my overall sound (I assume amplitude)? Do you know of any information regarding body tension? I haven't really found any research addressing this type of measurement. Thanks for any help you can provide!
+Jason Sulliman your lips do not produce the 440 Hz. Of course the 440 Hz tome, sound waves produced by your trombone, propagate in all directions. Also in the directions of your ears, lips and arms but the energy in the sound waves that reach your lips, arms and ears is insufficient to act as a driving force to make your lips, arms and ears noticeably vibrate at 440 Hz.
+Lectures by Walter Lewin. They will make you ♥ Physics.
But how than that be? I understand that the air inside the trombone will oscillate at 440Hz, but given the way the lips are moving air, *some* oscillation of air must happen in the other direction- I assume 440 in this example but at a different amplitude. I am interested in learning more about this phenomenon but no one seems to have done any research on it. I just don't understand how it could *not be a factor.
The more relaxed I am, the louder and fuller my sound is. I would go so far as to say larger players have an easier time producing larger sounds (I think) because the mass of their bodies contributes in some way to sound ia standing waves. Am I really way off base?
Thanks for getting back to me.
im a bit confused, if a violin is producing 440Hz then how is it producing much higher harmonics at the same time , aren't the frequencies for higher harmonics higher , coz length and speed are constant ?
+InventTwig If we displace the string in the same shape of one of the normal mode (the shape of a harmonic), it would vibrate in that mode with the respective frequency. But when we struck a string, it is usually not the case that the displacement is the same as one single mode. So depending on the shape of the displacement, the string will vibrate in the corresponding frequencies.
+InventTwig It cannot choose, it has NO choice. When you strike higher harmonics will be produced. I suggest you watch my 8.03 lectures about Fourier Analysis. I derive there e.g. which harmonics are excited if I plucked a string. https://www.youtube.com/watch?v=k3byqIaULb8&index=12&list=PLyQSN7X0ro22WeXM2QCKJm2NP_xHpGV89
This website contains all my 94 course lectures (8.01, 8.02 and 8.03) with improved resolution. They also include all my homework problem sets, my exams and the solutions. Also included are lecture notes and 143 short videos in which I discuss basic problems.
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