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.
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.
The transition from mundane earthly objects to awe-inspiring neutron stars and supernovas was incredible! Thank you for another great lecture, Professor!
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!
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, 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!
Your lectures make me feel like a kid again... sure the calculations get more and more complex as i go on, but both your infectious enthusiasm and seeing some questions from childhood, that i couldnt get out the back of my head, get answered is all the motivation i need. Thank you sir Lewin.
... 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. :-) :-) :-)
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 . 🇮🇳
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.
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
Lectures by Walter Lewin. They will make you ♥ Physics. ruclips.net/channel/UCiEHVhv0SBMpP75JbzJShqw 300+ videos. Many of them with high resolution. This channel has all my lectures and talks.
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
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..............
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! 😊
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.
Love you sir. Sir you are a gem for indian students preparing for IIT JEE. This topic specially is very irritating, but you made it very easy. Thanks a lot sir
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 🙋
*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
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"...:)
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.
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.
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.
@ 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
@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.
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.
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 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.
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.
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
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.
24:44 what happens to the rotational kinetic energy? I understand when you pull your arms in it increases and that comes from reduction of internal chemical energy used for the work to bring arms in. But when you pull your arms out how is energy conserved?? You lose rotational kinetic energy, but you don't gain any internal energy. Where does the lost kinetic energy go? Who gains that energy? I understand you could extend the arms almost effortlessly, but still in this case what balances the loss of KE in that closed system? (from the lab frame there is no centrifugal force)
Good question. To understand what happens to the rotational kinetic energy when his arms extend and his body slows down when rotating, consider a linear motion example. Suppose there is a 1 kg bottle of water on top of a 1 meter table above the floor. You pick it up, and carry it to set it gently on the floor. It starts at rest, and ends at rest, so something must've happened to the 9.8 Joules of potential energy in this example, as that energy cannot be in the bottle's kinetic energy. Your muscles generate thermal energy when they act as brakes for objects in motion, absorbing the work done on them, and dissipating the energy as heat. That's what happens to his rotational kinetic energy as well, when he extends his arms while rotating on that platform. The kinetic energy becomes work done on his muscles, and when work is done on a person's muscles, heat is dissipated. Since our bodies aren't built for regenerative braking of objects in motion, we also get tired from doing negative work on objects in motion, just as we would get tired from doing positive work to put objects in motion.
+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.
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.
Sir excellent class. Thanks again, I have to stop my self from writing excellent class every time I see one of your videos but I will make an exception here. Now I can see a supernova picture and really enjoy it. I agree with the people calling you an inspiration.
thanx for the lecture .. at time 11;11 in this lecture u said , gravitational force in this direction but graviational froce always act downward??? then how force become zero
+Harish Yadav downward on earth, but toward the larger body in space. I would watch earlier lectures for this (gravity is actually attractive force between all objects
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.
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.
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
Where can you start to derive the 10^46W term that you wrote at around 34:00. Is is the integral of the potential energy over the radius of collapse? And if so is mass m rewritten as rho*V, where V=Volume of the star?
@@lecturesbywalterlewin.they9259 sir only if you have written neutron star in the title of the video google will give me the result. I checked all the titles and nowhere stars were mentioned
how to calculate angular momentum of disc about point which is in the disc but away from center of mass and also about point out of the disc if the disc is rotating about those points? And also about center of mass if rotating about previously defined points?
If the object is not thrown upwards but is attached to the table at point P and made to rotate about point P (NOT the center of mass) rotational KE is 0.5I*w^2. I is the moment of inertia about the point P. The angular momentum about point P will be Iw. Watch my 8.01 lectures!
In the ice-skater's delight demonstration, when moment of inertia increases (ie hand is stretched) and omega decreases, rotational KE decreases.. so where does the energy go?
The work (negative or positive) is done by the skater when she changes her moment of inertia. When pulling her arms in she will have to do positive work.
Tq professor, but can I know the qualitative(that is without equation but physically ) definition of momentum. And what is caused by momentum, like acceleration is caused by force
Physics is not about equations, physics is about concepts. Linear momentum is conserved in collisions and angular momentum is conserved in the absence of an external torque. Those are VERY VERY powerful concepts. *Watch my 8.01 lectures!*
Lectures by Walter Lewin. They will make you ♥ Physics. Tq professor for responding so quickly 😊. U inspire me a lot. I used to hate physics till my teacher told me about ur lectures and now I love physics. And once again thank you for responding 😊
I could understand the conservation law of angular momentum when I was in 3rd or 4th grade. I knew that rotating bodies like wheels tend to keep the direction of their axes. Therefore, when I was in 5th grade, I felt confident to learn how to ride a bike because I knew that the bike would not fell as long as the wheels rotated. Is it correct? Is the bike based on the conservation law of angular momentum ? How did you calculate delta U when you shrink the sun to 10km?
Lectures by Walter Lewin. They will make you ♥ Physics. I think delta U should be negative because W gravity = delta K = -delta U => gravitational potential energy converted to kinetic energy. Did I misunderstand something?
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.
Can I say at 26:29 'since there are no external forces acting angular momentum is conserved'? If so, can I replace external torque with external force at 27:35?
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?
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 RUclips 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.
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
The transition from mundane earthly objects to awe-inspiring neutron stars and supernovas was incredible! Thank you for another great lecture, Professor!
My pleasure!
"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?
Prof. Lewin, you are a blessing. Thank you for making it open source.
"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
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, 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.
Your lectures make me feel like a kid again... sure the calculations get more and more complex as i go on, but both your infectious enthusiasm and seeing some questions from childhood, that i couldnt get out the back of my head, get answered is all the motivation i need. Thank you sir Lewin.
thanks for your kind words
... 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. :-) :-) :-)
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
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.
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 🙄
You are really dedicated sir.
Sacrifice for science .
For the love of physics
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
I was about to study fluid mechanics before i’ve been mesmerized by the explanations in this video.
been a mechanical engineer for over 25 years.. these are great stuff.
19:59 epic voice crack
Lectures by Walter Lewin. They will make you ♥ Physics.
ruclips.net/channel/UCiEHVhv0SBMpP75JbzJShqw
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.
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😢😢😢
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..............
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
👍🏻
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
Love you sir. Sir you are a gem for indian students preparing for IIT JEE. This topic specially is very irritating, but you made it very easy. Thanks a lot sir
Dear Sir, Thanks is not enough... Now I can understand that what a beauty in Physics! Love from Kishanganj Bihar India...
Prof. Lewin's lecture is always the best !
thankyou sir- i loved the supernova explosion picture!! THANKYOU SOS SO SO MUCH- YOU ARE AN INSPIRATION TO ME.
Best physics teacher ever!!!!!
Love you from Bangladesh!🇧🇩💝💝😍😍😍😍😍😍
Dear professor Lewin sir, your are a great concept clearer.
İlk defa bir fizik dersinde eğlendiğimi düşündüm..
Thanks for sharing with us.
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?
It's been an honour to study from you sir , thus I'm obliged to srudy from you for my jee exams
Sacrifice for the sake of science. Doesn't matter being a finance student, still I love Physics. Respect from INDIA 🇮🇳
still watching these lectures! i love it, I am 32 and everyday learning something new.
Wonderful!
thank you very much for your videos!
you make a giant difference in the world.
thank you Mark!
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
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.
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.
This lectures are pretty cool. I was a math student (working now) and i find myself watching this lectures. Cheers from portugal.
:)
thankeew soo much
love from india
These lectures surely do have a classical feel about them
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.
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.
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
You know this is going to be hard when there are two corrections in the first 9 minutes
Walter, your words about Jocelyn Bell were very nice.
Thanks sir, this is extremely useful for me, these videos are treasure for me
Glad to hear that
@ 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
And yes congratulations for 1 million subscribers 👌👌
@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.
awesome lecture sir . god bless you 💖💖💖
You are great sir....physics is real magic.
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
Please make a video on the application of physics in various real life situations 🙏🙏🙏🙏
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?
24:54 I am surprised He is perfectly spinning without feeling dizzy
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.
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.
Will watching these lectures help me in JEE
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
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.
ruclips.net/video/BPizQDIcQ70/видео.html
Absolute legend, Walter Lewin.
world best teacher
Thank you sir for this lecture you are a great physist in this world
It's my pleasure
Whoever are watching great lectures of him in 2024❤inspired from alakh sir
How can we determine the direction of angular momentum with just the vectors of velocity and direction? 6:43
do the cross product using the right hand rule
24:44 what happens to the rotational kinetic energy? I understand when you pull your arms in it increases and that comes from reduction of internal chemical energy used for the work to bring arms in. But when you pull your arms out how is energy conserved?? You lose rotational kinetic energy, but you don't gain any internal energy. Where does the lost kinetic energy go? Who gains that energy?
I understand you could extend the arms almost effortlessly, but still in this case what balances the loss of KE in that closed system?
(from the lab frame there is no centrifugal force)
Good question. To understand what happens to the rotational kinetic energy when his arms extend and his body slows down when rotating, consider a linear motion example. Suppose there is a 1 kg bottle of water on top of a 1 meter table above the floor. You pick it up, and carry it to set it gently on the floor. It starts at rest, and ends at rest, so something must've happened to the 9.8 Joules of potential energy in this example, as that energy cannot be in the bottle's kinetic energy. Your muscles generate thermal energy when they act as brakes for objects in motion, absorbing the work done on them, and dissipating the energy as heat.
That's what happens to his rotational kinetic energy as well, when he extends his arms while rotating on that platform. The kinetic energy becomes work done on his muscles, and when work is done on a person's muscles, heat is dissipated. Since our bodies aren't built for regenerative braking of objects in motion, we also get tired from doing negative work on objects in motion, just as we would get tired from doing positive work to put objects in motion.
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!!
Professor lewin u r awesome
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.
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*
How do you get the potential energy change at 34:08? I don't get it.
And we find amazing lecture on angular momentum
Sir excellent class. Thanks again, I have to stop my self from writing excellent class every time I see one of your videos but I will make an exception here. Now I can see a supernova picture and really enjoy it. I agree with the people calling you an inspiration.
+Mauricio Barda thanks for your kind words
thanx for the lecture .. at time 11;11 in this lecture u said , gravitational force in this direction but graviational froce always act downward??? then how force become zero
+Harish Yadav downward on earth, but toward the larger body in space. I would watch earlier lectures for this (gravity is actually attractive force between all objects
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.
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.
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.
Sir how can i get that assignment which are in description..
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
2:41 Respect sir.🙏
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
Do u also have a video on some most important common rotational questions involving the concepts
Professor Lewin, I wonder why non-conservative internal force of a rigid system do no work?
Where can you start to derive the 10^46W term that you wrote at around 34:00. Is is the integral of the potential energy over the radius of collapse? And if so is mass m rewritten as rho*V, where V=Volume of the star?
It's NOT 10^46 W it's J. It's the change in gravitational potential energy.
Sorry! Slip of the mind. But in any case where can you begin in order to find this number?
Take a spherical mass M of radius R2. Then change the radius of the star to R1 (R1
Thank you sir!
sir can you please in which lecture of 8.02 do you deal with magnetic fields around a neutron star
use google
@@lecturesbywalterlewin.they9259 sir only if you have written neutron star in the title of the video google will give me the result. I checked all the titles and nowhere stars were mentioned
please learn how to use google
en.wikipedia.org/wiki/Neutron_star
section 2.3
how to calculate angular momentum of disc about point which is in the disc but away from center of mass and also about point out of the disc if the disc is rotating about those points? And also about center of mass if rotating about previously defined points?
parallel axis theorem
thanks sir
if the disc is rotating about any point other than center of mass then if how can we calculate angular momentum about center of mass.
If the object is not thrown upwards but is attached to the table at point P and made to rotate about point P (NOT the center of mass) rotational KE is 0.5I*w^2. I is the moment of inertia about the point P. The angular momentum about point P will be Iw. Watch my 8.01 lectures!
In the ice-skater's delight demonstration, when moment of inertia increases (ie hand is stretched) and omega decreases, rotational KE decreases.. so where does the energy go?
The work (negative or positive) is done by the skater when she changes her moment of inertia. When pulling her arms in she will have to do positive work.
Thank you so much for answering!!
Professor can you please explain me the meaning of linear and angular "momentum" ,with an example.
watch my 8.01 lectures. It's all there!
Tq professor, but can I know the qualitative(that is without equation but physically ) definition of momentum. And what is caused by momentum, like acceleration is caused by force
Physics is not about equations, physics is about concepts. Linear momentum is conserved in collisions and angular momentum is conserved in the absence of an external torque. Those are VERY VERY powerful concepts. *Watch my 8.01 lectures!*
Lectures by Walter Lewin. They will make you ♥ Physics. Tq professor for responding so quickly 😊. U inspire me a lot. I used to hate physics till my teacher told me about ur lectures and now I love physics. And once again thank you for responding 😊
😊
I could understand the conservation law of angular momentum when I was in 3rd or 4th grade. I knew that rotating bodies like wheels tend to keep the direction of their axes. Therefore, when I was in 5th grade, I felt confident to learn how to ride a bike because I knew that the bike would not fell as long as the wheels rotated.
Is it correct? Is the bike based on the conservation law of angular momentum ?
How did you calculate delta U when you shrink the sun to 10km?
yes, the stability of a bike depends on angular momentum of the wheels. However, that not the only thing. Use google
Lectures by Walter Lewin. They will make you ♥ Physics. Does static friction force matter?
Lectures by Walter Lewin. They will make you ♥ Physics. I think delta U should be negative because W gravity = delta K = -delta U => gravitational potential energy converted to kinetic energy. Did I misunderstand something?
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.
Can I say at 26:29 'since there are no external forces acting angular momentum is conserved'? If so, can I replace external torque with external force at 27:35?
no
Lectures by Walter Lewin. They will make you ♥ Physics.
Isn't internal torque 0, because internal force 0 due to Newton's 3rd law?
I am sorry but I cannot add to the clarity of this lecture.
torque=dL/dt
zero torque => no change in L
Lectures by Walter Lewin. They will make you ♥ Physics.
How is newtons third law related to internal torque of the system?
ask google
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
Bless Walter Lewin for editing in his corrections