Also it would probably make some students and visitors feel awkward (like when people clap after pilot's graceful landing), and other teachers jealous enough to, I don't know, steal one of professor Lewis's fabulous pins?😅 I bet he feels rewarded far more seeing excellence in his students and their enthusiasm,or how the hall is always packed. And I hope his students will never cease to make him feel appreciated for cultivating love of learning and his unique teaching method.
@@margodphd It would? In my university it is normal / customary to applaud the professor (just not with clapping your hands but knocking on the table). Is that not just a sign of respect? But the pilot thing 100%, boomers are weird
I don't know what I'd have done without these lectures! They re-instill my passion in physics. You're a great man! Thank you for impacting the lives of many :)
I am in 11th right now and i read somewhere that watching Prof lewin's lectures would help me a lot for jee prep n they're amazing indeed 🙃 it's true you are father of physics legendary teacher
Whenever I do not understand a topic of what my physics teacher teaches, I come around and watch it from the professor and the topic becomes as clear as water. I would be delighted if you were my school physics teacher. Lots of respect for you from my side, professor :)
Indeed, nowadays this convertion of at least some of the "brake energy" is very common in almost all new cars, fossile fueled or electric/hybrids. I believe perhaps BMW was the first manufacturer to use it, in gasoline/diesel cars, maybe around 2006 or something? Many thanks for putting out these fantastic series for the benefit of students all over the globe! It is amazing! Greetings from Trondheim, Norway!
A great series of lectures. I went through graduate school in molecular biology and somehow came out the other end with very little knowledge of physics - it was mostly irrelevant to what I was doing at the time. So I am age 63 now and have decided to fill out my education, mostly because I wanted to understand the two Theories of Relativity, which are hard to appreciate if you do not know what led up to them. So I started studying more classical physics and now I am hooked. Among the sciences, physics has certainly achieved the most; asking questions about the age of the universe the underlying nature of the world, and showing us that it is stranger than anything we could imagine. I started out with the Caltech course “The Mechanical Universe” by David Goodstein filmed sometimes around the late 1970s (which for me makes it easy to imagine I am back in college). It is more than just a physics course, it is almost a course in the history of Western civilization, showing how the various ideas in physics evolved. Some of this is quite weird. Kepler, who was the first person to accurately describe the orbit of planets mathematically, was a kind of mathematical mystic, who believed that orbits of the planets should match Plato’s six ideal forms. Although this particular idea was wrong, the orbits turned out to follow perfect ellipses, so in a way he was on the right track. Of course we now take it for granted that we can describe all sorts of phenomena in the universe mathematically, but to step back to Kepler’s time - it is a bit odd that this should actually be true. I came to Dr. Lewin’s course because I found that the explanation of the mathematics was more complete, although as Dr. Lewin says, it is the concepts not the math per se that is important. “The Mechanical Universe” is also on RU-vid as are many of Richard Feymann’s lectures from an even earlier period. One thing that is interesting about watching these older physics courses is they mention ideas that are works in progress, and you have the great advantage of being able to zip forward to 2018 and find out what happened.
Must say sir, best online physics lectures I have ever seen. Straightforward, simple explanations, amazing demonstrations, and a legend of a teacher. I wish you well!
Dear sir , I have always been a lover of physics and now since I am in higher classes I am really feeling the way world works and your lecture gives me a way to connect my concepts in real world ,, the way you teach is really appreciable... Thanks for providing such gems free of cost!
Sir your lectures helped me alot to grab concepts of any problem in physics . I'm a lover of physics like you but because of the education system of India , I'm not able to focus further .. Literally here everyone is in race to acquire marks ,no one is in the track of understanding the concepts,my classmates also just memorize every term in our textbook ,it makes me annoying sometimes...BUT THE BEST PART WHEN I see your lectures is it helped to focus on that particular topic... Sir salute to you. If got a chance I want to be a student of yours... THANKS SIR
Don't forget: knowledge acquired memorizing disappears in few months, knowledge acquired understanding concepts lasts for the rest of your life. Then, if you're gonna attend Physics or Engeneering the notions you understood will help you in advanced classes whereas your classmates will have to start over learning/memorizing:)
I totally agree! It is highly painful sometimes when I want to think, imagine and enjoy some of the beatiful concepts of physics, and then I come to realise, as everyone here says, that I must solve these 40 problems a day, memorize theses whole lot of equations, and shut myself up for the sake of syllabus and these exams. It really feels awful.
Rotating rigid bodies - my favorite topic! A big thank you to professor Walter Lewin for getting the concept of rotational motion not in by head, but in my blood. I can feel the beauty of it all around! Here is a very cool demonstration that everyone can perform on their own. I was personally baffled when I first tried it. Take a book and shut it down with a tape or a rubber band. (Thin hard cover book preferred) Don't take a square book, by the way. What I want you to do now is throw it up in the air while giving it a spin. You have three ways to spin it. Let me tell you the axis' of rotations. Hold the book in both hand and take it in front of your eyes. All the axis of rotation goes through the center of mass. 1. Along an axis that goes from down to up. 2. Along an axis that goes from left to right. 3. Along an axis that goes straight through the book. Now that you know how to spin the book, give throw it up in the air while giving it a spin. NOTICE that there is one axis about which, if you spin it, it starts wobbling quite abruptly. It will be harder to catch the book when you spin along that axis. Try this demonstration and try to understand why it is happening. Hint: The axis that gives you unstable wobble is the axis through which the magnitude of moment of inertia in between the other two. Hope you like it!
It boggles my mind why he doesn't get a round of applause at the end, very few people have that ability to possess the power to understand, convey and keep up the thrill of the subject at the same time, salute to you
Yes Its true that this channel makes you love with physics ❤. Really your video helps lakhs of students to understand concepts easily. A HUGE THANKS FROM ALL OF US .
~18:00 Lol to be a physicist. None of those pesky engineering restraints. The flywheel is silly in a practical sense because of angular momentum and torque. Lewin will do an excellent demonstration on this phenomena in the next few lectures. I've no idea how a car will actually react to this flywheel but the physics is probably quite interesting. It's 2016 and this lecture was ~2002 I believe. He was right. People have been taking it seriously! In Formula 1 it's known as KERS - Kinetic Energy Recovery System. This is possible because of very powerful batteries that have been developed since the time of this lecture. PHYSICS PREDICTS THE FUTURE!!! (APPROXIMATELY)
The flywheel would need a universal mounting and enough space to move around, otherwise taking corners could get interesting. Of course, with more recent electric cars braking sends current back into the battery, so accomplishes the same thing.
@@marcinna8553 One could also use contra-rotational flywheels, so that the angular momentum of the two flywheels adds up to zero. This would eliminate the nuisance of gyroscopic effects getting in the way of steering.
Formula 1 cars actually use heat from the brakes to restore some electrical energy for their hybrid system. A modern perc predicted by dear Sir . Very cool
in all of this lesson there's only one thing blowing my mind...how the hell he does that trick with the chalk to make the point lines? all the rest is just trivial
put your finger in the middle and use the chuck from his head, it would "jump back" (beacuse of the 3th law, you use force so the board will give the chuck the same force back) when you'll slide it across a board
*8.01x lecture 19* Super AMAZING lecture. ------- 0:10 rotating object (review lecture 5) 5:13 moment of inertia (pure math) - kinetic energy of motion - “he is an astrophysicist” 🌎🌎🌎) 9:12 2 theorems of inertia to find moment of inertia -the parallel axis theorem -the perpendicular axis theorem (thin plates) 15:00 the department of energy (*Flywheel* - braking) - 21:15 US Energy DePARTMENT. *Physics is life! (Toy car - remember your childhood)* 26:08 the sun, the earth and the crab Pulsar’s rotation/ energy *(mind-boggling concept)* 34:49 some fantastic slides can blow your mind up -------- *See more here:* zyzx.haust.edu.cn/moocresource/data/20080421/U/01220/OcwWeb/Physics/8-01Physics-IFall1999/VideoLectures/detail/Video-Segment-Index-for-L-19.htm *Lecture notes and assignment in the description box:* -Lecture Notes, Flywheel Technology: freepdfhosting.com/5e0ffb03a1.pdf -Assignments Lecture 19 and 20: freepdfhosting.com/4a64566212.pdf -Solutions Lecture 19 and 20: freepdfhosting.com/972f51a6e8.pdf -------- *Thank you Prof. Walter Lewin, you are my best teacher.*
@@somethingaboutbrain 8.01 Physics Hans C. Ohanian Physics Volume 1 2nd edition W.W. Norton & Company ISBN 0-393-95748-9 8.02 Physics for Scientists & Engineers by Douglas C. Giancoli. Prentice Hall Third Edition ISBN 0-13-021517-18 8.03 Vibrations and Waves by Anthony French CRC Press ISBN 9780748744473 8.03 Electromagnetic Vibrations, Waves and Radiation by Bekefi and Barrett. The MIT Press ISBN 0-262-52047-8
21:10 With one flywheel the angular momentum would point perpendicular to or away from the road (depending on its rotational direction). When driving up a hill there will be a torque applied to the flywheel causing the net-momentum to flip the car over on either the left front and rear wheel or right front and rear wheel. I think in order to make the concept work, there have to be two counter-rotating flywheels to prevent the car from tipping over sideways when riding up or down a hill.
I never studied, did not show up to one lecture and avoided tutorials is physics, I just watch this man's videos before tests and get a 95% in the class
Considering the (i think previous) idea that decreasing moment of inertia has influenced the tectonic evolution of earth. Thanks for great lecture(s). peace and love
Hello Professor, I'm Himanshu from India , I'll be taking my JEE Advance examination next year and rotational mechanics is considered a very difficult topic, can you give some advice on how to feel the problems based on rotational mechanics and any material I should prefer. Is it possible to contact you through any media if possible. Thank you!
hello sir i really loves your lecture. I can remember the day when our physics teacher gives us lecture on damped harmonic motion in just 5 minute, i want to study that topic in more details and luckily i find your lecture on damped harmonic motion "vibration and waves" and from that time, and upto...... today i watch all of your lecture. I also got your book "for the love of physics" . I can't meet such a great conceptual teacher like you in my life. I really thankful to you. please accept my LOVE.
How are you, sir? I am a student from Egypt. I like your explanation very much, sir. But I have a problem downloading the files. They are closed. I wonder if they are available to university students only. Please reply from your honor.❤🥰
Thank you sir , for this great explanation, i am a jee aspirant and i was unable to understand rotational motion from my teacher. You make it easy for me . before this lecture rotation motion is a impossible task for me. Once again thank you sir , you are the best teacher.. Love you from India
Sir, a question: I just want to know what was your daily routine during 1)Your school days 2)Research 3)Teaching 4)Now We also want to know how hard you worked to become so successful in your life. We would be so happy if you make a video on this. Thank you so much once again sir. We love you a lot. May god (In your view, if exist) give you lots of health and hapiness. Please reply.
The lecture is from 2001 and Hubble was already in orbit by then, still you guys didn't have the a Visible Spectrum of the Crab Nebula, i guess it hadn't been assigned the observation yet.
Loved the lecture.. if the crab nebula is projected to stop in 1000 years and it is at a distance of 5000 light years from us.... doesn't it mean it has already stopped but we have not yet observed it?
For Question 1 in Problem Set 6 (ie. the Serious Car Crash problem), I arrive at a different answer for part (c) (ie. the acceleration of each vehicle with respect to the ground) when I solve the Kinematics equation: v2^2 = v1^2 + 2a(x2-x1) in the Ground Reference Frame, as opposed to the Center of Mass Reference Frame! Can anyone point out my conceptual error here (what am I missing?)
Literally two seconds in and this stuff starts making sense... I know my physics professor is trying his best but I wish he would take this approach more and leave the "turbo encabulator" stuff out when teaching fundamental concepts.
This is one fabulous vest, Professor. I always wondered what is the source of the quirky, large pins (like the strawberry one) is that I've seen You wear during previous lectures in this series, they are quite unique.
In the the problem where tennis ball is kept on a basketball what is the physical reason for the much greater height acheived by the ball?. Also, when we work in the approximation where the speed of basketball after collision is still "v", isn't conservation of energy violated in this approximation?
Sir I have a question I also love physics about the theories and concepts and but when it's time for numericals I stucked don't know why my mathematics is notvery nice but I have a curiosity to study space and astronomy so what can I do ?
Start with arithmetic, most of math involves concepts to derive an expression but when working the actual problem having a good foundation of arithmetics will make it easier. Studying number theory really helped me with the understanding what to expect out of the behavior of any given number. I might just be dumb though.
I'm curious as to how we can see the Crab nebula pulsar that was born roughly 1,000 years ago 5,000 light years away? Do X and gama rays travel at 5x the speed of light? What did I misunderstand from the lecture?
Always curious to know what next you will tell in ur lecture . U are just incomprehensible. The best Prof of this decade. Made me love❤️ physics. Sir I have been watching ur lecture since my 9th grade. Thanks for all the things I got because of you. :-)
I. A cube and a cylinder, both with the same masses, are let go from the top of an incline with friction, at the same time. They'd arrive at the bottom at the same time right? Their translational acceleration would be the same. The friction force would do negative work on the cube which'd be converted to heat, while it'd be doing work rotating the cylinder, giving off no heat, assuming the contact point does not slide. Is this correct? Assuming all the negative work is fully converted into heat. II. The same cylinder rolling down the incline with friction, but this time the translational acceleration exceeds the tangential one, causing the contact point to slide during rolling. When this happens, the friction force would do negative work and give off heat right? To calculate the heat generated by the work of the friction, the slope angle of the incline θ, grav. constant g, the friction coefficient k, mass of cylinder m, radius r, angular acceleration α, and the time it takes for the cylinder to roll down from the top to the bottom, t. Assuming the friction force stays constant throughout the motion. Translational acc. of the contact point being g(sinθ-kcosθ), and deriving the tangential acc. from the torque 1/2*α*m*r^2=kmgcosθr, the αr equals 2kgcosθ. The contact point would slide with the total acceleration of gsinθ-3kgcosθ, and the negative work done by the friction force, thus the heat, would equal 1/2*(gsinθ-3kgcosθ)*t^2*kmgcosθ right? I have a few more questions but they require me to draw the free body diagrams and vectors to explain them properly. Do you have some form of contact, like e-mail or..? Thanks in advance.
Part I: Not enough information. We would need to know the coefficient of kinetic friction for the cube and the incline, to know which would accelerate faster down the incline (the cube or the cylinder). We would also need to know the incline angle. In the special case that (1 - mu_k/tan(theta)) = 2/3, then the cylinder and block would have the same acceleration. The friction force is ultimately a zero work force, when it is in the static regime. Just like the normal force. So the friction force isn't doing any work to cause the cylinder to roll. The gravity does work, but the friction doesn't. The friction is just a force of constraint. Part II: In the event that the cylinder rolls WITH slip as opposed to rolling without slip, then yes, the force of kinetic friction will do negative work on it. The friction force that would cause it to roll with an angular acceleration consistent with its center's linear acceleration, wouldn't be strong enough to do so, and it would slide too fast for its angular acceleration to keep up. Kinetic friction would cause the angular acceleration, but not enough of it.
Keep in mind that MIT is only a very mediocre University. That's why only 101 people who studied at MIT or who lectured there received a Nobel Prize. *That's very embarrassing.* Luckily you got a much better education.
since crab pulsar is slowing down so in order to conserve angular momentum its moment of inertia should also increase. so change in kinetic energy should be L^2/2I minus initial K.E. (or i am wrong somewhere). thanks sir in advance.
professor Lewin. I dont understand something. How is it possible in the crab pulsar that the rotation energy converts in radiation energy? greetings from colombia
Sir, suppose we have a disc, along with a massless axel, attached to its centre, the disc is initially in ground, the axel then provides a torque, however when the disc attempts to rotate, ground will provide a frictional force, now the acc of the point touching the ground will be determined by both the torque and the frictional force, however the acc of centre of mass is solely due to friction, my doubt is if the net acc of the bottom point touching ground turns out to be zero, will the centre of mass not be in rest?
Dr. Lewin At 29:13 you predict that by slowing the Earth down over a period of 1 year so that after 1 year the 24 hour time period increases by 2.4 second, we can recover the energy necessary for annual global consumption. I tried crunching some numbers myself but it seems i made a grave error because I am not getting any where near 2.4 seconds. I was wondering how you did that calculation... may i please get a hint? Did you start by assuming that in billion years all rotational energy would be used up to calculate the increase in the period or was it the other way around?
rotational Kin energy of the Earth is 0.5*I*omega^2. Calculate first I, then use the 2 different values of omega and you will be able to get the correct answer!. If all else fails: "cheat". en.wikipedia.org/wiki/Rotational_energy
Lots of physics concepts getting clear now specially inertia. What a wonderful teacher. My physics teacher (Ranchhod Patel) was also very good and encouraging. Still i know his name.
29:17 Slow the earth by about 2.4 seconds ? You didn't say any particular way of doing that after all you say it's fantasy But if u think of it We will be able to do that anyways As more and more tall buildings are being constructed each day the moment of inertia is getting bigger as well And by the conservation of angular momentum the angular speed has to go down Won't that be enough to slow down the earth by 2.4 seconds(after lot of years obviously)?
Wonderful lecture as always! I've got a question, during the talk about pulsars you said it wasn't well understood why, but the pulsar on the Crab Nebula was "blinking" at us, by that I inferred that it wasn't something predicted in the equations, so how did they know that it was the pulsar that was blinking when they adjusted the frequency to obtain the pictures? Since they didn't know wich one was the pulsar and they didn't know the pulsar would blink, how did they know that the pulsar was the blinking one and found the frequency? Thanks for your amazing work!
I am a huge fan of yours, Professor Lewin. I came from a high school where the teachers seem to be allergic to actually teaching the material. Some of the teachers in my high school do not even know what they are supposed to be teaching. For example, I had to teach myself the parallel axis theorem. Although I know the material fairly well because I spent a lot of time teaching myself, I still learn a great deal from your videos. I am highly into physics, and your videos continue to make me love the material. I do not need to take any more physics courses in college, but your videos do not fail to interest me.
Please can you say what the course text book is? I enjoy the lectures but also sometimes want to have a good set of notes/a book as a reference to flick to when I need it
I have watched physics lecture videos from other reputable universities, here, on RU-vid, but they seem pale in comparison to MIT's Prof. Walter Lewin...it's the mannerism and style of the lectures, examples and experiments during the lectures that seem to reach out to lay-persons...thus inviting curious souls to engage and learn from Prof. Lewin...
Today ( jun 15 '23) a study by Saio et al. was published, showing (on the basis of carbon almost being burnt up) that Betelgeuse is possibly only decades away from going supernova. A very exciting idea that this may happen in our lifetimes. It is 10 times closer than the 1054 supernova which created the crab nebula, the event will be visible even during daylight. It will most likely become a neutron star, Orion will never look the same... As a neutron star specialist, what are the most exciting observational opportunities if this happens?
Professor , Can't we get the car down the hill with the help of engine alone ......how does gravity work . Could we get we get the car down the hill in the absence of gravity.
>>>Could we get we get the car down the hill in the absence of gravity.>>> in the absence of gravity you can go up a mountain down into a valley - all you have to overcome is air drag and friction with the road.
Everything is beyond on concepts even all equations and formulas derived from concepts so its most important to give priority to concepts by not learning only equations like a slab
these are great lectures. i am using them to study for my upcoming physics 101 test, but i cant seem to find anything regarding the theory of relativity. did i just miss it or is it not available?
Yes we find moment of inertia about any line then we can find across any other line by moment of inertia + md^2 where d is the distance between the given line respect to which moment of inertia has been found and we have found moment of inertia about ring and disc 1/2 mi^2..
Do you have a lecture which contains the calculation of center of mass (But in a different way, it's something like density of mass, because mass is not equally distributed and symbol is lambda for rods. It's an integration of m/l or something.)
professor how do they convert mechanical energy to magnetic energy ? I just wanna know the name of the phenomenon or just something relevant ,I searched for it on the internet but didn't find anything,can you give me any search terms or something please :? thank you ps: ive watched all you 8.02x videos
+InventTwig You first convert mechanical energy to electrical energy. Then you use the electric energy to create magnetic fields in a solenoid. henrykolm.weebly.com/mit-magnetic-lab-1961-82.html
Dear Walter Lewin thank you so much for the best lectures in physics around the world. I have a question: how to you get the 2.5 seconds per year more for the period? That´s not what i am getting. I get something like 7.1E-5 which is much smaller!
Professor Lewin, can you please explain Moment of Inertia of Circular Ring about diametrical axis, exams like JEE are taking it to be (MR^2)/2, But I don`t think circular ring is a Planar Lamina, I thought when ring rotates fast about diameter it looks like a hollow sphere, so I used 2(MR^2)/3 (I might be wrong, but I had to think in the exam, that`s the best reasoning I was able to come up with), but even JEE (Mains) took it to be (MR^2)/2, so, please explain the correct Moment Of Inertia of ring about diameter, if it really is (MR^2)/2, then please explain how...... thank you sir
@@lecturesbywalterlewin.they9259 Sir, on google they are using perpendicular axis theorem on the circular ring, but it is not a planar lamina, also sir, I really love your lectures, I did watch some, I planned on watching all, they really help increase my love for physics, But I have JEE exam, and this exam has become way too formula based, I cant do anything but postpone the wonderful physics lectures for now and focus of memorizing the formulae that can easily be noted down and looked at when needed for application, but we cant use formula books in jee, and we dont have enough time to derive the formula,...... And about the question, you said for perpendicular axis theorem to be applicable, it should be a plate like object (in 8.01 Lect19), but ring is not plate like, is perpendicular axis theorem still applicable for diametrical axis of a circular ring
Please explain the spinning top problem that is touted as the one that lies in heart of classical mechanics I find it so counterintuitive in many ways if you could shed some light on this I would be very grateful
