Dear professor Lewin, I think you've made an enormous contribution to Science by inspiring thousands of young students and showing the beauty of Physics. I'm studying to become a scientist and your amazing lectures are extremely helpful. Thank you!
I taught many courses during a 30 year career teaching engineering. Dynamics was my favorite course. I learned something new every time I taught it. I find your lectures very informative. I really appreciate how you corrected your mistakes in your lecture and I am sure your students do too.
The transition from mundane earthly objects to awe-inspiring neutron stars and supernovas was incredible! Thank you for another great lecture, Professor!
cheers from Brazil, I've recommended your lessons in 8.01 to all my classical mechanics classmates, and we have emulated almost all your experiments so far.
This part of mechanics is also considered to be the toughest in the entire JEE syllabus, but Professor Lewin made it crystal clear in my head. Thank you sir!
"If you have problems with this, you are not alone" A very good sign off for physics students. I remember having trouble in my classes thinking I was completely missing the point. It developes over time and I learned far too late that everyone else were experiencing the same.
Thankkk you so much for recording this lectures. I live in Turkey!! At my university, I can't really get inspiring classes to love Physics. But the last 20 minutes of this lecture had a concern to inspire us about the Physics and the nature. I study Physics and you, sir, are making me inspired on your every lecture!
Lectures by Walter Lewin. They will make you ♥ Physics. czcams.com/channels/iEHVhv0SBMpP75JbzJShqw.html 300+ videos. Many of them with high resolution. This channel has all my lectures and talks.
Sir, I would just like to thank you for your excellent teaching. I was extremely confused after my physics professor taught (a much worse version of) this lecture, but watching your video cleared up all questions I have. Your detail and clarity are second to none; certainly the best teacher of physics I have ever seen!
Hello professor, I sometimes feel all of this so mind boggling! We humans were able to understand stuff which are sooo far away, by just using the laws of physics! It was a really great lecture! Thank you professor! 😊
for those of you curious about the calculation preformed at ~34:22. you need to calculate the potential energy of the star (which is ofcourse spherical) in the 2 cases (R = 7*10^5 km and R = 10 km); that is the work required to bring all the particles of the star from infinity to their respective positions on the sphere.
Sir, it was so good of you to mention Jocelyn Bell in your lecture. I recently watched a documentary of her by The New York times, 'Almost Famous'. Even though she did not get any recognition, she is still happy.
I am a 15 yr old from India ( Bharat ) and preparing for jee. I want to thank you. Your lectures are extremely helpful. Professor, My love for physics started just because of you . 🇮🇳
... and after all these years... a few days ago, Jocelyn Bell finally *was* awarded the Nobel prize she's deserved all this time. As I understand it, she intends to donate the entire cash-award part of her prize. I know nothing of her financial circumstances, but even most well-off people would be unlikely to be so magnanimous with "windfall" wealth. You do know her, so please offer her a *whacking* high-five from me, won't you? :-)
Thank you so much for correcting me, Walter: I won't make that mistake again. She *deserves* the recognition and more all the same, but the Nobel snub still rankles. What amazes me is that (as you and others have described her) she's humble, gracious and generous enough to let all that slide *and* offer up her huge cash prize to support others. Yeah... a woman can be a mensch. :-) :-) :-)
Dear professor, Even if I fail my physics course I just want to show my gratittude to you: I've always hated physics since 7th grade and I can finally find it interesting and enjoyable, as it is! You really have a gift for teaching, every matter is very clear now, thank you so much!
Dear sir I m from india i wanna say that you are phenomenal u make me love PHYSICS which i hated Thanks a lot loads of respect sir hope u live for million years and make futures of students all around tge world
SOMEONE IN THE COMMENTS SAID that these lectures was delivered in 2002 when I was not in that world but after a long time in 2019 I'm watching it ..and it is also helpful for me but a little bit because 1st reason is that I don't know english too much and 2nd reason is i am studying physics but i am in lower level e.g 11 class and in our course ,there is no too much details ..BUT SIR YOU ARE GOOD TEACHER...APPRECIATION FROM MY BEAUTIFUL COUNTRY PAKISTAN..............
I am from India and I literally love your lectures as they make me feel physics . I am gonna rock my test. I am understanding all the concept....to clear jee advanced its highly recommendable sir to watch your videos Lots of love from India
Thankyou Sir, for sharing such a beautiful lecture with us. I live in India, and I am a senior high school student. I have watched many lectures of 8.01x and 8.02x several times over since they all are densely packed with knowledge but they all made my concepts crystal clear.
yup...i saw ur playlist ...but the problem is the all have japanese title...nd i don't know japanese language...all i know is ...."watashi wa bhanu te imashu"...:)
*This channel was created in Febr 2015 by my Dutch friend Daniel Dekkers.* It has become way more popular than "For the Allure of Physics" (created in Dec 2014) which also carries my 94 MIT course lectures + my Farewell Lecture at MIT "For the Love of Physics" of May 16, 2011. That lecture alone has been viewed by more than 6 million people.
Sir, you have always been an inspiration to me and your lectures always motivate me to pursue my dream of getting into research and studying astronomy.....only the fact that you replied makes me feel so special. Believe it or not but this is like a blessing to me. -Regards
Sir I am in class 11 from India and I am preparing for jee I really appreciate your work in physics and your ability in teaching I am feeling honoured to get the knowledge of physics I am definitely not so rich to pay the expensive fees here in institutes I will grateful and lucky to attend your lectures thank you sir love from India 🙋
If you have finished 8.01, 8.02 and 8.03 then go to MIT OCW and watch 8.04 and after that 8.05. 8.05 is lectured by Barton Zwieback. He is a very good lecturer, I have attended several of his lectures at MIT.
At 2:49 maybe {r(perp.)c} represents the perpendicular distance of point Q from center of mass of M. And suppose the body is in pure translation , then , we do not need to consider rhe rotational Angular momentum.
if an object is in pure translation then there is angular momentum relative to all points except points on the "straight" line of the movement. Depending on the problem you need to solve this angular momentum can be CRUCIAL and can not be ignored.
sir,,,i am a little confused at 24:45 as you are pulling your arms nearer to the axis of rotation you are accelerating as your angular velocity keeps on increasing and finally reaches its maximum value due to conservation of angular momentum but to provide an angular acceleration there must be some external force acting on the system which is absent here, then how you are accelerating,,, like if we take an example of a bomb blast into two fragments each fragment gets some velocity due to internal forces but if we look at each fragment separately then this internal force is actually external for them which makes their velocity from 0 to a certain value but to the whole system the net force is 0.i,e we can actually visualize what forces are giving them velocities here..........but in this case of increasing angular velocity what is going on? or IT IS NOT NECESSARY TO HAVE A NET EXTERNAL TORQUE ON THE SYSTEM TO PROVIDE IT AN ANGULAR ACCELERATION??
Given a body that remains rigid that cannot redistribute its mass, a torque is required to change its angular velocity, i.e. for it to have an angular acceleration. For a system that CAN redistribute its mass internally, an external torque is not the only way to give it an angular acceleration. Redistributing the mass, and changing the moment of inertia, will cause its angular velocity to change. There is a torque that acts on a body as it moves radially in a rotating reference frame, and this is a consequence of the Coriolis effect. It is this internal torque that occurs between Professor Lewin and the two barbells, that enables the barbells to apply a torque to speed him up. Try walking along the radial handrail on a spinning merry-go-round, and you will experience this effect. You will feel an apparent force pulling you tangentially forward, when you walk radially inward, and you will feel an apparent force pulling you tangentially backward, when you walk radially outward. To stay at the same position as the handrail, you experience a constraint force as a reaction to these apparent forces that are a consequence of the Coriolis effect. The constraint force (tension or compression in your arms) is what enables the speed of the merry-go-round to change, as you redistriute the mass of the system by moving radially on it.
@ 26:18 For others confused like me, Even though the points are at different distances from Q --> r1 & r2 ... the torques are equal in magnitude since r1sin(theta1) = r2sin(theta2) ... the component of distance perpendicular to direction of force
My notes : 1.Momentum Intrinsic ,angular momentum is not,it depends on point about which it is calculated .2. Angular momentum about C,representing Centre of circle,is constant,.while momentum is changing,in uniform circular motion . 3.V at every point of disk is different but angular velocity is not. 4.Angular momentum is always constant about any point in space for rotation about center of mass,spin angular momentum is thus intrinsic and unique ,e.g earth rotation about axis. You could then talk about THE Angular momentum.
In 1054 everyone who could write was possibly more concentrated on the great Schisma in the Christian Church between the Latin Church and the Greek Orthodox Church. It could be an explanation, there are however mentions of a similar occurance but 2 month earlier. I cannot explain this, but the mention in the Chinese literature is from 3 centuries later.
CAN'T STRESS THE IMPORTANCE OF THE FIRST 17 MINS. OF THIS LECTURE ENOUGH! But, of course, the Earth has no INTRINSIC angular momentum (17:02)! The spinning around its own axis is not intrinsic, but a consequence of the way our solar system is created.
The angular momentum of a particle performing uniform circular motion is L. If the kinetic energy of particle is doubled and frequency is halved, then angular momentum becomes???????? I think the answer should be (√2)L but the answer given in L/4 .............. who is correct??
KE=0.5mv^2, L=mvR, v=omega*R thus L is also m*omega*R^2. KE is also 0.5m*(omega*R)^2. To double the KE and at the same time to reduce omega by a factor of 2, R^2 will have to go up by a factor of 8, thus L will go up by a factor of 4.
Spin angular momentum of the Earth is an intrinsic property it's omega*I. Orbital angular momentum of the Earth is ONLY conserved relative to the Sun, NOT relative to any other point. If you choose a point somewhere on the orbit, when the Earth is at that point the orbital angular momentum relative to that point is ZERO.
If its rotational inertia remains unchanged (individual rigid body), it requires a net torque to act upon it, in order to have an angular acceleration. An object can have angular acceleration without torque, while changing its rotational inertia. Unlike linear inertia (i.e. mass), that requires changing the identity of the body to change its mass (like a rocket loosing its propellant mass, or farm equipment collecting a harvest), rotational inertia can change just by redistributing the mass. As you can see with the turntable demonstration in this lecture.
@35:25 the supernova explosion *did not* occur in the year 1054, that's when it was observed! It happened 5,000 years before that date or whatever the distance to the Crab Nebula is in light years.
Please, Sir! Don`t answer if it´s too complicated for you to explain it ,ok? Why don´t earth (in the orbital moviment ) looses energy ( as an electron would do in its hipotetical orbital movement around the nucleus) and go into an spiral moviment towards the final colision with the sun? Sorry about my English! You are our hero!!!!!
Yes you got it. In classical physics accelerated charges produce EM waves. That's the result of Maxwell's eqs. However, in Newtonian mechanics masses that are accelerated do not radiate any energy. HOWVER, in GR (Einstein) accelerated masses do radiate energy; in the form of gravitational waves (GW). The acceleration of the Earth in orbit (v^2/R) is so low that it cannot even be measured. However, two black holes in a close binary system radiate a large amount of energy (GW). Thus the orbits shrink and ultimately they wil merge, the black holes will spiral into each other producing a HUGE "last Surge of GW. This was first observed on Sept 14, 2015 with LIGO. LIGO was perceived 40 years ago by my friend Rai Weiss (former colleague of mine at MIT). I predict that he will share the Nobel Prize of Physics this year for that fabulous result. GW were predicted 100 years by Einstein.
+Gautham Umashankar No I have not taught 8.05 at MIT. It's taught in general by theoreticians. At present you can take the 8.05x course on EdX. It's taught by Professor Barton Zwiebach. He is a great teacher.
36:58 Supernova not recorded in Europe is not mystery if European history between 4-12 century was counterfeited. Star of Bethlehem could be supernova, meaning 1053 years could be stolen from official history later by clergy in Renessance in 15-16 c.
sir in your turn table experiment treating your central body and arms as different parts. if we see your central body will have increased angular velocity and angular moment um should then increase how so.is conservation of angular momentum not valid then
In the absence of external torque, angular momentum is conserved. Watch my "ice skater" demo. I*omega is conserved. If I increase I omega goes down and vice versa.
At 27:50-28:07 the radius and moment of inertia go down on a star, so obviously the angular velocity will go up. But he misses a very valuable point which lead to the discovery I made. The star actually loses mass. He is assuming as the star shrinks and its moment of inertia goes down, the mass does not change. Yet, all stars have solar wind and flare out trillions of tons of matter. So they are clearly losing mass. So more correctly, it is the radius shrinks, the moment of inertia shrink, and the mass shrinks, meaning the angular velocity will remain constant. This is a major issue that is not addressed for unknown reasons, I guess it amounts to them assuming they have no evidence for stars that have lost a large majority of their mass. I beg to differ. They call them "exoplanets/planets". Saying there is no evidence for stars that have lost a large portion of their mass by calling them by a different name is very peculiar.
>>>which lead to the discovery I made>>> When did you make that discovery? Mass loss of a supernova explosion (not overlooked by me) has been known for more than half a century. When the core of a 20 solar mass star collapses it leaves behind some 19 solar masses streaming out at velocities of some 20,000 km/sec AND it leaves behind an approx 1.4 solar mass neutron star whose rotation period can be 1 second or even less. en.wikipedia.org/wiki/Supernova
Thank you so much for sharing all these marvelous lectures with us ! I am currently in high school and binge watching through all your videos . I have one question from this lecture and it would be great if you could help me out with it! In 33:39 , you estimated the amount of energy released as the radius shrinks but mass remains unchanged... i was wondering how I could calculate the amount of energy released? Can I get any clue or relations that I could get started with? Thanks!
Sir , I have confused about angular momentum is not beeing intrinsic property while momentum is an intrinsic property. As the angular momentum depends on the point we chose, aren`t the momentum also depends on frame of reference. It seems to me both of them are not intrinsic property.
Namaste Sir, (Indian greetings) Please help me!! A thin rod AB of mass M and length L is rotating with angular speed w about vertical axis passing through its end B on a horizontal smooth table. If at some instant the hinge at end B of rod is opened then, can you please explain why the angular momentum of the rod remains conserved about the center of mass of the rod during the whole process? And I have another one sir A cylinder of height h , diameter h/2 and mass M and with a homogeneous mass distribution is placed on a horizontal table. One end of a string running over a pulley is fastened to the top of the cylinder, a body of mass m is hung from the other end and the system is released. Friction is negligible everywhere. Strings and pulleys can be assumed to be light. At what minimum ratio of m/M will the cylinder lift?
I like watching these video. I would like to see an explanation about how gas can collapse on itself since gravity is small force compared to electromagnetic force . There must be something more than F=GmM/r2.
I have a question about the right-hand rule, if whatever is in the z-axis is "coming out of the blackboard," does that make it negative, and going into the blackboard positive?
If an object of mass m is rotating about its com with angular momentum A and if it is also translating with velocity V, then the angular momentum relative to any point P is A + m*dXV, d is the position vector from P to the com. X indicates cross product.
@@manohardivi2593 The explanation I've heard for why angular momentum is called L, is that the letter L looks like two perpendicular vectors, as is common with cross products. Just about any symbol that might seem to be a more logical choice (a, alpha, m, mu, even pi as the counterpart to p for momentum), is already spoken-for in mechanics, so the symbol was selected for its appearance instead of pronunciation. Some books use H for Hamilton, when L has another full time job.
Sir, I want to ask something that confused me. If there is no net external torque, the angular momentum is conserved. That's ok. But if there is no net external torque, then the rotational kinetic energy must be also conserved, is that True? But if the angular momentum is conserved, we can immediately see from mathematical expressions that the rotational kinetic energy is not conserved.If one of them is conserved, the other one is not conserved and we conclude it from their mathematical expressions. How can it be? How can rotational kinetic energy is not conserved while angular momentum is conserved? Can you help me please?
if angular mom is conserved then wI is conserved. If I goes down Stellar collapse the w goes up. *Rotational KE increases* the work is done by gravity. I have a Physics problem #101 in which I do a demo at home. I pull a string, thus I do work, Iw is constant I goes down, w goes up rot KE increases. czcams.com/video/x66ckZO4Hxg/video.html
@@lecturesbywalterlewin.they9259 Oh professor!! Thank you so much!! What an excellent sphere it is! A very good demonstration. But when the sphere expanses, it's rotational KE decreases, and does a resistive Force do work in this case? Thank you!!
Manish Singh you are welcome. This website "Lectures by Walter Lewin. THey will make you love Physics" is the ONLY complete site. It has all my lectures. enjoy! \\/\///////////
Hello Prof Lewin, if there is a mouse on the edge of a rotating disk and we know the moment of inertia of the disk about the centre of mass, then we can find the total moment of inertia which includes the moment of inertia of the mouse measured with respect to the CM of disk. Lets say this disk is moving with constant w. Then the mouse moves towards the center of mass of the disk. Then we can use conservation of Angular momentum to get the new angular velocity. But which moment of inertia do we use for when the mouse is in the centre of mass of the disk. Is it just the moment of inertia about the CM of the disk without the mouse on it, or has the mass of the mouse affected the moment of inertia of the disk about the centre of mass? Thank you!
Thanks for the lectures professor, you really make me love physics and I'm in such love, that i was thinking in give up my course to start a physics course!
Hello Walter Lewin! When you were on the turntable you had your angular momentum L conserved. Your rotational KE was L^2/2I, I being your moment of inertia. When you drew in your hands I decreased so your rotational KE must have increased. Where did you get that KE?
At 34:00 you calculated change in gravitational potential energy. But as much I know gravitational potential energy is due to gravitational pull between two objects. so with which object this gravitional pull to the star is being considered?
I cannot add to the clarity of my lecture in which I define Grav PE (zero at infinity). --MmG/r (r being the distance of m to the center of M). Watch my lecture again or use google
Dear professor Lewin, I think you've made an enormous contribution to Science by inspiring thousands of young students and showing the beauty of Physics. I'm studying to become a scientist and your amazing lectures are extremely helpful. Thank you!
+Alex Zilio Thank you Alex for your kind words. I am delighted that my lectures are "extremely" ,helpful for you.
I completely agree.
@@frankdimeglio8216 in your way
After filling lakhs of fees, real knowledge is found on CZcams for free.🔥
Respect for sir🙏
I taught many courses during a 30 year career teaching engineering. Dynamics was my favorite course. I learned something new every time I taught it. I find your lectures very informative. I really appreciate how you corrected your mistakes in your lecture and I am sure your students do too.
Yes, you are right.
The transition from mundane earthly objects to awe-inspiring neutron stars and supernovas was incredible! Thank you for another great lecture, Professor!
My pleasure!
cheers from Brazil, I've recommended your lessons in 8.01 to all my classical mechanics classmates, and we have emulated almost all your experiments so far.
Excellent!
Hi
Prof. Lewin, you are a blessing. Thank you for making it open source.
"you passed the course" i love his lectures :D
This part of mechanics is also considered to be the toughest in the entire JEE syllabus, but Professor Lewin made it crystal clear in my head. Thank you sir!
How your jee exam went?
Can i prefer his lectures for my jee prep?
"If you have problems with this, you are not alone"
A very good sign off for physics students. I remember having trouble in my classes thinking I was completely missing the point. It developes over time and I learned far too late that everyone else were experiencing the same.
Thankkk you so much for recording this lectures. I live in Turkey!! At my university, I can't really get inspiring classes to love Physics. But the last 20 minutes of this lecture had a concern to inspire us about the Physics and the nature. I study Physics and you, sir, are making me inspired on your every lecture!
You're very welcome!
Which university do you study
Lectures by Walter Lewin. They will make you ♥ Physics.
czcams.com/channels/iEHVhv0SBMpP75JbzJShqw.html
300+ videos. Many of them with high resolution. This channel has all my lectures and talks.
Lectures by Walter Lewin. They will make you ♥ Physics. sir, the link is down. please check.
Sir, I would just like to thank you for your excellent teaching. I was extremely confused after my physics professor taught (a much worse version of) this lecture, but watching your video cleared up all questions I have. Your detail and clarity are second to none; certainly the best teacher of physics I have ever seen!
Thank you for your kind words.
You are really dedicated sir.
Sacrifice for science .
For the love of physics
I was about to study fluid mechanics before i’ve been mesmerized by the explanations in this video.
Hello professor,
I sometimes feel all of this so mind boggling! We humans were able to understand stuff which are sooo far away, by just using the laws of physics! It was a really great lecture! Thank you professor! 😊
You are very welcome
👍🏻
19:59 epic voice crack
for those of you curious about the calculation preformed at ~34:22. you need to calculate the potential energy of the star (which is ofcourse spherical) in the 2 cases (R = 7*10^5 km and R = 10 km); that is the work required to bring all the particles of the star from infinity to their respective positions on the sphere.
Sir, it was so good of you to mention Jocelyn Bell in your lecture. I recently watched a documentary of her by The New York times, 'Almost Famous'. Even though she did not get any recognition, she is still happy.
I am a 15 yr old from India ( Bharat ) and preparing for jee.
I want to thank you.
Your lectures are extremely helpful.
Professor, My love for physics started just because of you . 🇮🇳
Best of luck
Prof. Lewin's lecture is always the best !
been a mechanical engineer for over 25 years.. these are great stuff.
... and after all these years... a few days ago, Jocelyn Bell finally *was* awarded the Nobel prize she's deserved all this time. As I understand it, she intends to donate the entire cash-award part of her prize. I know nothing of her financial circumstances, but even most well-off people would be unlikely to be so magnanimous with "windfall" wealth.
You do know her, so please offer her a *whacking* high-five from me, won't you? :-)
she did not get the Nobel Prize
instead she got a $3.5 million prize which is way more than a Nobel Prize. I have congratulated her!
Thank you so much for correcting me, Walter: I won't make that mistake again. She *deserves* the recognition and more all the same, but the Nobel snub still rankles.
What amazes me is that (as you and others have described her) she's humble, gracious and generous enough to let all that slide *and* offer up her huge cash prize to support others.
Yeah... a woman can be a mensch. :-) :-) :-)
Dear professor Lewin sir, your are a great concept clearer.
Dear professor,
Even if I fail my physics course I just want to show my gratittude to you: I've always hated physics since 7th grade and I can finally find it interesting and enjoyable, as it is! You really have a gift for teaching, every matter is very clear now, thank you so much!
class 7 e ami physics er namE jantam na 🙄
Dear sir
I m from india i wanna say that you are phenomenal u make me love PHYSICS which i hated
Thanks a lot loads of respect sir hope u live for million years and make futures of students all around tge world
SOMEONE IN THE COMMENTS SAID that these lectures was delivered in 2002 when I was not in that world but after a long time in 2019 I'm watching it ..and it is also helpful for me but a little bit because 1st reason is that I don't know english too much and 2nd reason is i am studying physics but i am in lower level e.g 11 class and in our course ,there is no too much details ..BUT SIR YOU ARE GOOD TEACHER...APPRECIATION FROM MY BEAUTIFUL COUNTRY PAKISTAN..............
I am from India and I literally love your lectures as they make me feel physics . I am gonna rock my test. I am understanding all the concept....to clear jee advanced its highly recommendable sir to watch your videos
Lots of love from India
Best of luck!
Can you give me suggestion to which video i should watch in this channel😢😢😢
thankyou sir- i loved the supernova explosion picture!! THANKYOU SOS SO SO MUCH- YOU ARE AN INSPIRATION TO ME.
still watching these lectures! i love it, I am 32 and everyday learning something new.
Wonderful!
Dear Sir, Thanks is not enough... Now I can understand that what a beauty in Physics! Love from Kishanganj Bihar India...
It's been an honour to study from you sir , thus I'm obliged to srudy from you for my jee exams
Best physics teacher ever!!!!!
Love you from Bangladesh!🇧🇩💝💝😍😍😍😍😍😍
İlk defa bir fizik dersinde eğlendiğimi düşündüm..
Thanks for sharing with us.
These lectures surely do have a classical feel about them
thank you very much for your videos!
you make a giant difference in the world.
thank you Mark!
Thankyou Sir, for sharing such a beautiful lecture with us. I live in India, and I am a senior high school student. I have watched many lectures of 8.01x and 8.02x several times over since they all are densely packed with knowledge but they all made my concepts crystal clear.
You are most welcome
thankeew soo much
love from india
now thats i call teaching it his best....best teacher i have seen in my life.
Bhanu Sharma Thank you Bhanu
really from dumb to pro .... credit goes to sir walter lewin ... n to ... thnxx for uploading whole course ...good work
Bhanu Sharma click on "playlist" you view wayyyyyyy more than my course lectures alone!
yup...i saw ur playlist ...but the problem is the all have japanese title...nd i don't know japanese language...all i know is ...."watashi wa bhanu te imashu"...:)
all have Japanese titles ????????????
For me all have English titles. Why are your Japanese?
This is absurd.
I really thank the person who has made this channel......feel so privileged to watch Mr.Walter Lewin's lectures at a click of a button.
*This channel was created in Febr 2015 by my Dutch friend Daniel Dekkers.*
It has become way more popular than "For the Allure of Physics" (created in Dec 2014) which also carries my 94 MIT course lectures + my Farewell Lecture at MIT "For the Love of Physics" of May 16, 2011. That lecture alone has been viewed by more than 6 million people.
Sir, you have always been an inspiration to me and your lectures always motivate me to pursue my dream of getting into research and studying astronomy.....only the fact that you replied makes me feel so special. Believe it or not but this is like a blessing to me.
-Regards
Sir I am in class 11 from India and I am preparing for jee I really appreciate your work in physics and your ability in teaching I am feeling honoured to get the knowledge of physics I am definitely not so rich to pay the expensive fees here in institutes I will grateful and lucky to attend your lectures thank you sir love from India 🙋
How much are you scoring in Physics in JEE Advanced Mock Tests per paper of around 66 marks , and which coaching institute?
sir, when will 8.04 and 8.05 be uploaded...waiting..
I really started loving physics
If you have finished 8.01, 8.02 and 8.03 then go to MIT OCW and watch 8.04 and after that 8.05. 8.05 is lectured by Barton Zwieback. He is a very good lecturer, I have attended several of his lectures at MIT.
This lectures are pretty cool. I was a math student (working now) and i find myself watching this lectures. Cheers from portugal.
:)
Thanks sir, this is extremely useful for me, these videos are treasure for me
Glad to hear that
At 2:49 maybe {r(perp.)c} represents the perpendicular distance of point Q from center of mass of M. And suppose the body is in pure translation , then , we do not need to consider rhe rotational Angular momentum.
if an object is in pure translation then there is angular momentum relative to all points except points on the "straight" line of the movement. Depending on the problem you need to solve this angular momentum can be CRUCIAL and can not be ignored.
Sacrifice for the sake of science. Doesn't matter being a finance student, still I love Physics. Respect from INDIA 🇮🇳
Walter, your words about Jocelyn Bell were very nice.
You know this is going to be hard when there are two corrections in the first 9 minutes
FAST in China announced the first pulsar it detected and that bring me back here. Thank you Prof. Lewis
SUPERRRRR en.wikipedia.org/wiki/Five_hundred_meter_Aperture_Spherical_Telescope
Excellent lecture Sir. Thanks and Regards 🙏🙏🙏🙏🙏🙏🙏🙏🙏
Most welcome
sir,,,i am a little confused at 24:45 as you are pulling your arms nearer to the axis of rotation you are accelerating as your angular velocity keeps on increasing and finally reaches its maximum value due to conservation of angular momentum but to provide an angular acceleration there must be some external force acting on the system which is absent here, then how you are accelerating,,,
like if we take an example of a bomb blast into two fragments each fragment gets some velocity due to internal forces but if we look at each fragment separately then this internal force is actually external for them which makes their velocity from 0 to a certain value but to the whole system the net force is 0.i,e we can actually visualize what forces are giving them velocities here..........but in this case of increasing angular velocity what is going on?
or IT IS NOT NECESSARY TO HAVE A NET EXTERNAL TORQUE ON THE SYSTEM TO PROVIDE IT AN ANGULAR ACCELERATION??
Given a body that remains rigid that cannot redistribute its mass, a torque is required to change its angular velocity, i.e. for it to have an angular acceleration.
For a system that CAN redistribute its mass internally, an external torque is not the only way to give it an angular acceleration. Redistributing the mass, and changing the moment of inertia, will cause its angular velocity to change.
There is a torque that acts on a body as it moves radially in a rotating reference frame, and this is a consequence of the Coriolis effect. It is this internal torque that occurs between Professor Lewin and the two barbells, that enables the barbells to apply a torque to speed him up.
Try walking along the radial handrail on a spinning merry-go-round, and you will experience this effect. You will feel an apparent force pulling you tangentially forward, when you walk radially inward, and you will feel an apparent force pulling you tangentially backward, when you walk radially outward. To stay at the same position as the handrail, you experience a constraint force as a reaction to these apparent forces that are a consequence of the Coriolis effect. The constraint force (tension or compression in your arms) is what enables the speed of the merry-go-round to change, as you redistriute the mass of the system by moving radially on it.
You are great sir....physics is real magic.
@ 26:18 For others confused like me,
Even though the points are at different distances from Q --> r1 & r2 ... the torques are equal in magnitude since r1sin(theta1) = r2sin(theta2) ... the component of distance perpendicular to direction of force
Thank you
My notes : 1.Momentum Intrinsic ,angular momentum is not,it depends on point about which it is calculated .2. Angular momentum about C,representing Centre of circle,is constant,.while momentum is changing,in uniform circular motion . 3.V at every point of disk is different but angular velocity is not. 4.Angular momentum is always constant about any point in space for rotation about center of mass,spin angular momentum is thus intrinsic and unique ,e.g earth rotation about axis. You could then talk about THE Angular momentum.
And yes congratulations for 1 million subscribers 👌👌
awesome lecture sir . god bless you 💖💖💖
In 1054 everyone who could write was possibly more concentrated on the great Schisma in the Christian Church between the Latin Church and the Greek Orthodox Church. It could be an explanation, there are however mentions of a similar occurance but 2 month earlier. I cannot explain this, but the mention in the Chinese literature is from 3 centuries later.
CAN'T STRESS THE IMPORTANCE OF THE FIRST 17 MINS. OF THIS LECTURE ENOUGH! But, of course, the Earth has no INTRINSIC angular momentum (17:02)! The spinning around its own axis is not intrinsic, but a consequence of the way our solar system is created.
The angular momentum of a particle performing uniform circular motion is L. If the kinetic energy of particle
is doubled and frequency is halved, then angular momentum becomes????????
I think the answer should be (√2)L but the answer given in L/4 .............. who is correct??
KE=0.5mv^2, L=mvR, v=omega*R thus L is also m*omega*R^2. KE is also 0.5m*(omega*R)^2. To double the KE and at the same time to reduce omega by a factor of 2, R^2 will have to go up by a factor of 8, thus L will go up by a factor of 4.
thnx
Professor lewin u r awesome
sir, does the spin angular momentum remains the same for any reference point but orbital angular momentum does not
Spin angular momentum of the Earth is an intrinsic property it's omega*I. Orbital angular momentum of the Earth is ONLY conserved relative to the Sun, NOT relative to any other point. If you choose a point somewhere on the orbit, when the Earth is at that point the orbital angular momentum relative to that point is ZERO.
Brilliant Lewin Sir
sir I have a question. sir whenever there is angular accelration on particle there is always an torque acting on it. is am I right
yes, that is correct
torque=I*alpha. alpha is dw/dt
If its rotational inertia remains unchanged (individual rigid body), it requires a net torque to act upon it, in order to have an angular acceleration. An object can have angular acceleration without torque, while changing its rotational inertia.
Unlike linear inertia (i.e. mass), that requires changing the identity of the body to change its mass (like a rocket loosing its propellant mass, or farm equipment collecting a harvest), rotational inertia can change just by redistributing the mass. As you can see with the turntable demonstration in this lecture.
Thank you sir for this lecture you are a great physist in this world
It's my pleasure
world best teacher
@35:25 the supernova explosion *did not* occur in the year 1054, that's when it was observed! It happened 5,000 years before that date or whatever the distance to the Crab Nebula is in light years.
And we find amazing lecture on angular momentum
24:54 I am surprised He is perfectly spinning without feeling dizzy
We would love to see you in a conversation with Sadhguru. He has been to MIT twice, as a guest lecturer.
Susan Jocelyn Bell Burnell donated her $3.000.000 prize in 2018.
Please, Sir! Don`t answer if it´s too complicated for you to explain it ,ok? Why don´t earth (in the orbital moviment ) looses energy ( as an electron would do in its hipotetical orbital movement around the nucleus) and go into an spiral moviment towards the final colision with the sun? Sorry about my English! You are our hero!!!!!
Yes you got it. In classical physics accelerated charges produce EM waves. That's the result of Maxwell's eqs. However, in Newtonian mechanics masses that are accelerated do not radiate any energy. HOWVER, in GR (Einstein) accelerated masses do radiate energy; in the form of gravitational waves (GW). The acceleration of the Earth in orbit (v^2/R) is so low that it cannot even be measured. However, two black holes in a close binary system radiate a large amount of energy (GW). Thus the orbits shrink and ultimately they wil merge, the black holes will spiral into each other producing a HUGE "last Surge of GW. This was first observed on Sept 14, 2015 with LIGO. LIGO was perceived 40 years ago by my friend Rai Weiss (former colleague of mine at MIT). I predict that he will share the Nobel Prize of Physics this year for that fabulous result. GW were predicted 100 years by Einstein.
well , professor does black hole is spinning very fast as it''s moment of inertia is negligible , i think?
physics.stackexchange.com/questions/310881/do-black-holes-have-a-moment-of-inertia
www.quora.com/Does-inertia-exist-inside-black-holes
Please make a video on the application of physics in various real life situations 🙏🙏🙏🙏
Amazing lecture sir.... Thanks for motivating us to love physics. Have you taught general relativity and 8.05 quantum mechanics sir??
+Gautham Umashankar No I have not taught 8.05 at MIT. It's taught in general by theoreticians. At present you can take the 8.05x course on EdX. It's taught by Professor Barton Zwiebach. He is a great teacher.
+Lectures by Walter Lewin. They will make you ♥ Physics. Thanks a lot sir!!
From tamilnadu india...
Simply amazing!
36:58 Supernova not recorded in Europe is not mystery if European history between 4-12 century was counterfeited. Star of Bethlehem could be supernova, meaning 1053 years could be stolen from official history later by clergy in Renessance in 15-16 c.
sir in your turn table experiment treating your central body and arms as different parts. if we see your central body will have increased angular velocity and angular moment um should then increase how so.is conservation of angular momentum not valid then
In the absence of external torque, angular momentum is conserved. Watch my "ice skater" demo. I*omega is conserved. If I increase I omega goes down and vice versa.
czcams.com/video/BPizQDIcQ70/video.html
At 27:50-28:07 the radius and moment of inertia go down on a star, so obviously the angular velocity will go up.
But he misses a very valuable point which lead to the discovery I made. The star actually loses mass. He is assuming as the star shrinks and its moment of inertia goes down, the mass does not change. Yet, all stars have solar wind and flare out trillions of tons of matter. So they are clearly losing mass.
So more correctly, it is the radius shrinks, the moment of inertia shrink, and the mass shrinks, meaning the angular velocity will remain constant.
This is a major issue that is not addressed for unknown reasons, I guess it amounts to them assuming they have no evidence for stars that have lost a large majority of their mass. I beg to differ. They call them "exoplanets/planets". Saying there is no evidence for stars that have lost a large portion of their mass by calling them by a different name is very peculiar.
>>>which lead to the discovery I made>>>
When did you make that discovery?
Mass loss of a supernova explosion (not overlooked by me) has been known for more than half a century. When the core of a 20 solar mass star collapses it leaves behind some 19 solar masses streaming out at velocities of some 20,000 km/sec AND it leaves behind an approx 1.4 solar mass neutron star whose rotation period can be 1 second or even less. en.wikipedia.org/wiki/Supernova
sir u took moment of inertia of dish has mr^2 but the moment of inertia is 1\2mr^2 ????
The moment of inertia of a hoop is Mr^2, and the Cylinder is 1\2mr^2.
Bless Walter Lewin for editing in his corrections
Thank you so much for sharing all these marvelous lectures with us !
I am currently in high school and binge watching through all your videos .
I have one question from this lecture and it would be great if you could help me out with it!
In 33:39 , you estimated the amount of energy released as the radius shrinks but mass remains unchanged...
i was wondering how I could calculate the amount of energy released? Can I get any clue or relations that I could get started with?
Thanks!
total energy (KE + PE) is conserved. When the star implodes the PE decreases (the smaller R the less PE) thus KE goes up.
@@lecturesbywalterlewin.they9259 so to work out the loss in PE, work out the increase in rotational KE?
Sir , I have confused about angular momentum is not beeing intrinsic property while momentum is an intrinsic property. As the angular momentum depends on the point we chose, aren`t the momentum also depends on frame of reference. It seems to me both of them are not intrinsic property.
Thanks for your time!
I sent you a revised version of my earlier answer. Plse read it.
Namaste Sir, (Indian greetings) Please help me!!
A thin rod AB of mass M and length L is rotating with angular speed w about vertical axis passing through its end B on a horizontal smooth table. If at some instant the hinge at end B of rod is opened then, can you please explain why the angular momentum of the rod remains conserved about the center of mass of the rod during the whole process?
And I have another one sir
A cylinder of height h , diameter h/2 and mass M and with a homogeneous mass distribution is placed on a horizontal table. One end of a string running over a pulley is fastened to the top of the cylinder, a body of mass m is hung from the other end and the system is released. Friction is negligible everywhere. Strings and pulleys can be assumed to be light. At what minimum ratio of m/M will the cylinder lift?
I like watching these video. I would like to see an explanation about how gas can collapse on itself since gravity is small force compared to electromagnetic force . There must be something more than F=GmM/r2.
gas collapse onto itself during core collpase of a star (supernova explosiion) *BECOZ of GRAVITY*
I have a question about the right-hand rule, if whatever is in the z-axis is "coming out of the blackboard," does that make it negative, and going into the blackboard positive?
x X y = z that's a righthanded coordinate system. PERIOD it does not matter how you draw it as long as x X y = z.
@@lecturesbywalterlewin.they9259 okay, thank you
how do we find the angular momentum of an object(rotating about it's centre of mass) about a point other than it's com
If an object of mass m is rotating about its com with angular momentum A and if it is also translating with velocity V, then the angular momentum relative to any point P is A + m*dXV, d is the position vector from P to the com. X indicates cross product.
Best teacher!
:)
Sir why angular momentum is denoted by alphabet L?
L for Lewin
@@lecturesbywalterlewin.they9259 😅😅😅
@@manohardivi2593 The explanation I've heard for why angular momentum is called L, is that the letter L looks like two perpendicular vectors, as is common with cross products. Just about any symbol that might seem to be a more logical choice (a, alpha, m, mu, even pi as the counterpart to p for momentum), is already spoken-for in mechanics, so the symbol was selected for its appearance instead of pronunciation. Some books use H for Hamilton, when L has another full time job.
Excellent. Thank you
:)
Sir, I want to ask something that confused me. If there is no net external torque, the angular momentum is conserved. That's ok. But if there is no net external torque, then the rotational kinetic energy must be also conserved, is that True? But if the angular momentum is conserved, we can immediately see from mathematical expressions that the rotational kinetic energy is not conserved.If one of them is conserved, the other one is not conserved and we conclude it from their mathematical expressions. How can it be? How can rotational kinetic energy is not conserved while angular momentum is conserved? Can you help me please?
if angular mom is conserved then wI is conserved. If I goes down Stellar collapse the w goes up. *Rotational KE increases* the work is done by gravity. I have a Physics problem #101 in which I do a demo at home. I pull a string, thus I do work, Iw is constant I goes down, w goes up rot KE increases. czcams.com/video/x66ckZO4Hxg/video.html
@@lecturesbywalterlewin.they9259 Oh professor!! Thank you so much!! What an excellent sphere it is! A very good demonstration. But when the sphere expanses, it's rotational KE decreases, and does a resistive Force do work in this case? Thank you!!
15:57 imp point
Love From A JEE Aspirant
Sir i love physics so much that i have got tatooed two times e=mc² and another one is integral tatoo on my bicep love you from india.sir
Thnx a Million for uploading this and all other videos !
Manish Singh You are welcome
Manish Singh you are welcome. This website
"Lectures by Walter Lewin. THey will make you love Physics" is the ONLY complete site. It has all my lectures.
enjoy!
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+Lectures by Walter Lewin. They will make you ♥ Physics. Would you ever consider doing another complete lecture series? These are so fantastic.
Hello Prof Lewin, if there is a mouse on the edge of a rotating disk and we know the moment of inertia of the disk about the centre of mass, then we can find the total moment of inertia which includes the moment of inertia of the mouse measured with respect to the CM of disk. Lets say this disk is moving with constant w. Then the mouse moves towards the center of mass of the disk. Then we can use conservation of Angular momentum to get the new angular velocity. But which moment of inertia do we use for when the mouse is in the centre of mass of the disk. Is it just the moment of inertia about the CM of the disk without the mouse on it, or has the mass of the mouse affected the moment of inertia of the disk about the centre of mass? Thank you!
the answer is in my 8.01 lectures. WATCH them or use google
Absolute legend, Walter Lewin.
Thanks for the lectures professor, you really make me love physics and I'm in such love, that i was thinking in give up my course to start a physics course!
:)
Hello Walter Lewin! When you were on the turntable you had your angular momentum L conserved. Your rotational KE was L^2/2I, I being your moment of inertia. When you drew in your hands I decreased so your rotational KE must have increased. Where did you get that KE?
yes it increased. As I pulled my arms in, I had to do work.
At 34:00 you calculated change in gravitational potential energy. But as much I know gravitational potential energy is due to gravitational pull between two objects. so with which object this gravitional pull to the star is being considered?
I cannot add to the clarity of my lecture in which I define Grav PE (zero at infinity). --MmG/r (r being the distance of m to the center of M). Watch my lecture again or use google