8.01x - Lect 7 - Weight, Weightlessness in Free Fall, Weight in Orbit

This Lecture is a Must. Weight - Perceived Gravity - Weightlessness Free Fall - Zero Gravity in Orbit (Misnomer). Great Demos
Assignments Lecture 5, 6, 7 and 8: freepdfhosting.com/95e6843397.pdf
Solutions Lecture 5, 6, 7 and 8: freepdfhosting.com/4984cbb7f1.pdf

[@nitotech]

I love his phrase "Non negotiable"

[@rajaradi802]

Niotech ..............?

[@glkglkglkglk9193]

@@rajaradi802 he ends any fact with that phrase "non - negotiable"

[@makara2711]

the reason why you love the phrase is because you find it interesting, that is NON NEGOTIABLE

[@yupitzmeeee]

200th

[@oximas-oe9vf]

@@makara2711 lmao

[@VitoOporto3D-WORLD]

Dear professor Lewin (WL). your lectures are just wonderful. You planned the lectures in a highly professional manner. I noticed how clever you are in dividing the presentation into segments that make so much sense, I mean the order of events, whether you start with a formula(F), a video(V), or a practical experiment(Pe), it helps us understand the complicated issues with ease. We know how much you really love physics. My mother always told me: "Believe in yourself, and others will believe in you" - After watching you, we believe in you and we love physics(LP). Thanks! -- LP = WL(Pe+V+F)/t ---obviously, measured in Lewins.

[@lecturesbywalterlewin.they9259]

thanks for your kind words

[@lecturesbywalterlewin.they9259]

@@noelleleger232 *WRONG* if the only force acting on an object is gravity, then it is in free fall and it will have no weight! But ofcoz due to the gravitational force it may change both speed and also direction. If a planet is in a circular orbit, its speed does not change but the gravitaional force keeps it in orbit. Called centripetal force. All this is covered in my 8.01 lectures. *All this is very very ellementary high school Physics*

[@davidmudry5622]

@@lecturesbywalterlewin.they9259 The tennis ball? Now it has weight, and now it has even more weight because I am accelerating it. Question: Anytime the tennis ball has weight means it is being accelerated...True or False?

[@davidmudry5622]

@@lecturesbywalterlewin.they9259 You say gravity is a Force and every action has an equal and opposite Force...isn't it a contradiction to say in Free Fall there is only the Force of gravity acting on a body without any equal and opposite REACTION..?

[@tonibat59]

Prof Lewin is defining weight as the force that opposes the gravitational force, if any, from whatever source it comes. Whether it is from a string, the floor, or a scale in the bathroom. But these guys in Aeronautics call their experiments 'zero gravity', and I think they are not being disingenuous or careless. There's a case to call it zero gravity. In the ref frame of the free falling body, there's no way you can prove that any gravity exists. Just like in the Galileo experiment with the observer in the cabin of a ship, where he could never prove that there is a speed, a laboratory full of physicists in free fall, even with Prof Lewin inside it (God forbid!) they would never be able to proof that there is any gravity. Of course, they would not have time to publish their (negative) result 😢😅 The conclusion would be, since the laws of physics must be the same for all observers, not only the inertial ones, that for that free falling unfortunates, there is no gravity. There are some interesting, not well understood issues here that could be highlighted by some thought experiments.

[@rkcoder]

I have no need for these lectures in terms of university/exams yet these lectures are still a joy to watch. What a professor Walter Lewin is.

[@manikantan4809]

now you are not studying,you are learning !

[@tomoakhill8825]

I have a doctorate in physics from the University at the other end of Mass Ave. I am watching these because he is so much fun to watch. With my experience I keep thinking these are too simple for MIT students, but then I think about it, and no these _physics_ lectures, and physics is the most crunchy of the hard sciences, so the intro physics lectures cover the same material at every university in the world.

[@gabrielv2100]

If we had a teacher like you i think we could have been in love with Physics from the beginning! Thank you so much for this! You are a great man!

[@lecturesbywalterlewin.they9259]

Thank you Gabriel

[@davidmudry5622]

@@lecturesbywalterlewin.they9259 Question...according to Newtonian physics are the astronauts in the space station weightless because the forces of up and down are equal and opposite? And according to Newtonian physics do we have weight on a bathroom scale because the forces of up and down are equal and opposite?

[@davidmudry5622]

@@lecturesbywalterlewin.they9259 What is weight, what is acceleration? You get on a Bus and you have to stand, you instinctively hold onto something even though the Bus is not moving yet. You are standing still, and with respect to forward and backward acceleration there is no forward or backward acceleration yet, and you are weightless with respect to the front and back of the Bus and to holding onto something until the Bus starts moving and stopping. So far you only have weight pushing down because you are only being accelerated in the opposite direction.

[@davidmudry5622]

@@lecturesbywalterlewin.they9259 In Newtonian physics we say gravity pulls you down accelerating you down at 9.8 m/s/s and the bathroom scale has a normal force pushing you up so you will stand still. Is the normal force also accelerating you up at 9.8 m/s/s..?

[@davidmudry5622]

@@lecturesbywalterlewin.they9259 at 35:54 you said when you accelerate the hi-tech scale down it weighs a little less...do realize that the twin towers accelerated from 1300 feet down to the ground at 64% of free fall acceleration? How would you explain that?

[@thienthanhtranoan6723]

0:20 introduce bathroom scale and elevator scale (3 cases/ decelerate, accelerate, weightless - result when a=g free-fall) + example 9:30 example roller + (tension - spring massless) + explain the result + prediction ( similar: elevator scale) 20:45 experiment around a circle (ac) (similar elevator scale) 25:50 weightless ex with a bucket of water (such amazing) (4 phases of this cases: normal weight, weightless, increase weight, normal weight) 34:40 an experiment with a device By Pro. Dave + a graph show u is incredible / physics here 39:35 zero gravity experiment (zero weight/ zero gravity) - airplane - sickness 47:25 video about weightlessness/ take risk for the future of science and technology

[@anandapatmanabhansu]

Thankyou

[@davidmudry5622]

You say gravity is a Force and every action has an equal and opposite Force...isn't it a contradiction to say in Free Fall there is only the Force of gravity acting on a body without any equal and opposite REACTION..?

[@margodphd]

This professor is the antithesis of the (in my opinion unfair and insulting) parable that "Those that can,do and those that can't - teach". It takes additional levels of excellence to be able to explain difficult concepts with such clarity, yet in way that inspires curiosity. The amount of lives and careers one excellent teacher can influence is incredible - it propagates, like waves in water, one group of minds shaping another, all inspiration emanating from one person. We need to appreciate teachers, or we'll all loose.

[@davidmudry5622]

You say gravity is a Force and every action has an equal and opposite Force...isn't it a contradiction to say in Free Fall there is only the Force of gravity acting on a body without any equal and opposite REACTION..?

[@keithcomess8669]

Prof. Lewin: You are a gifted and inspiring teacher! You've performed a great service by posting these lectures for those unfortunate enough to have not seen and learned from you in person.

[@AA-pz5sk]

I'm totally in love with physics now, it's 3:26 am here btw and I don't wanna sleep listening to this lectures, and i can only imagine how my life could have been as having a teacher like you in my highschool days, you're so good Sir.

[@lecturesbywalterlewin.they9259]

Best of luck!

[@davidmudry5622]

You say gravity is a Force and every action has an equal and opposite Force...isn't it a contradiction to say in Free Fall there is only the Force of gravity acting on a body without any equal and opposite REACTION..?

[@sgreducation553]

I free fall in Love with physics by seeing this kind of lecture

[@Dr10Jeeps]

I am a retired university psychology professor. I love watching KZbin videos on physics, especially quantum mechanics and cosmology. After discovering Dr. Lewin's lectures I admire his true teaching genius. Thank you professor Lewin.

[@lecturesbywalterlewin.they9259]

:)

[@RealDukeOfEarl]

I'll never get over those dotted lines. Brilliant in so many ways, sandals and socks jumping off desks, the madman. These lectures deserve a round of applause at the end. It used to be customary.

[@lecturesbywalterlewin.they9259]

thanks for your kind words

[@lecturesbywalterlewin.they9259]

@noelleleger232 *WRONG* if the only force acting on an object is gravity, then it is in free fall and it will have no weight! But ofcoz due to the gravitational force it may change both speed and also direction. If a planet is in a circular orbit, its speed does not change but the gravitaional force keeps it in orbit. Called centripetal force. All this is covered in my 8.01 lectures. *All this is very very ellementary high school Physics*

[@mylesbishop1240]

At the 30 min mark you can just tell he was on fire! In the flow of teaching

[@lecturesbywalterlewin.they9259]

:)

[@noorulhakeem]

I am a doctor of liver and stomach - absolutely no relation with these topics, but trust me I've enjoyed it alot. I wish someone would've taught it this way in our college days. Back then, physics seem to be an imaginable subject and everytime it would start with, "let's suppose this". But watching these videos, it makes alot of sense and these students are lucky. A subject that was considered boring, has made so much interesting by Prof that a medical doctor is watching it - for HOURS! KUDOS to you sir.

[@lecturesbywalterlewin.they9259]

It's gretat that you watch my lectures; many medical doctors are watching my lectures.

[@jagadishchandra3142]

You'reperfectly right

[@davidmudry5622]

@@lecturesbywalterlewin.they9259 If you are to compare the Sun’s gravity with that of the Earth, it is 28 times stronger and bigger than the earth. Some experts say gravity is a force that pulls objects, and they will accelerate as they are pulled in free fall towards a massive body, such as a planet or a star. Einstein said gravity is not that kind of force, and that objects in free fall are not being pulled nor are they accelerating. If we imagine the earth had a larger gravitational pull, perhaps of 9g instead of 1g, would a person need a g-suit while accelerating down in free fall, or would a person need a g-suit when in a state of being at rest while lying down on the ground? The resting g-tolerance of acceleration for a typical person is anywhere from 3-5 g acceleration depending on the person. A g-suit will typically add 1 g of acceleration tolerance to that limit. Pilots still need to practice the 'g-straining maneuver' that consists of tensing the abdominal muscles in order to tighten blood vessels so as to reduce blood pooling in the lower body. High g is not comfortable, even with a g-suit. In older fighter aircraft, 6 g was considered a high level, but with modern fighters 9 g or more can be sustained structurally[citation needed] making the pilot the critical factor in maintaining high maneuverability

[@flow1465]

Well, I didn't know that you have your lectures on KZbin and this KZbin page is managed none other than you! Walter Lewin your way of teaching is extraordinary. You just don't tell us the bookish stuff, but also tell us how it works practically and that's fascinating. I was confused about this topic and many others, but now I can't say that anymore, I just found about your lectures yesterday and I think I am going to love physics now. Thank you :)

[@lecturesbywalterlewin.they9259]

Thanks Batman for your kind words

[@flow1465]

Lectures by Walter Lewin. They will make you ♥ Physics. Oh! You really replied.Well, it's my pleasure sir.

[@pilo5000]

Who wouldn't reply to Batman

[@davidvalle3068]

I loved physics but my physics professor made me hate it because he goes so slow and is uncharamatic, but I go here and he reminds me why I like be physics

[@brocklesnar2546]

@@lecturesbywalterlewin.they9259 Hey wasssuupp

[@johnkendal8303]

These students are very fortunate to have such a passionate lecturer .

[@jianuflavian6451]

i wish i had such good professors when i was young .... , i am 42 years old and i just love waching and learning .... you Professor Walter Lewin are indeed a treasure,

[@Diwakarc007]

Thank your Lewin. Your explanations are so clear and experimental, that to go through this course, one does not even need to take a pen and paper. Just following along is more than enough. Thank you.

[@vitaminprotien1644]

I like the cameraman.....he always shows us some funny stuff 🤣

[@OrganicDefender000]

I have been struggling with understanding gaining or loosing weight in an elevators for 1.5 years. Now it's all clear to me just because of your brilliant ability to teach and my imagination. You are a great teacher. A great teacher's success does not lie in teaching his students, but making sure they attain it. And you have that. Thank you professor Lewin, you have helped me so much!

[@davidmudry5622]

You say gravity is a Force and every action has an equal and opposite Force...isn't it a contradiction to say in Free Fall there is only the Force of gravity acting on a body without any equal and opposite REACTION..?

[@trishitchandra1549]

While watching your soothing lectures over and over I found a very fascinating visualization of accelerating objects. When you make a dotted line I notice that the line itself a mind blowing example of such kind. When the gaps between successive points increases it's accelerating (mainly the first half of the line) and reverse for deceleration (the last half) . And for constant gaps its 0 acc. I use this fact by showing your videos to my friends...for them to understand and visualize the beauty of accelerating bodies. You are really an inspiration for my love of physics. ❤

[@aditya4sure]

The way you explain is amazing, The weightlessness is indeed amazing, I wish I was born earlier(I am 17 though) to be a part of your lecture in person... I really think that I missed a lot professor. You are Beyond Awesome, So far So good. I wish you live 100 years more!!

[@ihsansusanto989]

i just discovered that i'm in love with physics thanks to your lectures, thank you Professor Walter Lewin, greetings from Indonesia

[@lecturesbywalterlewin.they9259]

You are very welcome

[@dranilsaxena]

Dear sir, I am astonished by your method of explanations. These are very clear and lucid. I have been explaining the physical phenomenon in a similar manner. I am a solar cell scientist with a PhD in Physics on SIS type of Si Solar cells from IIT Delhi, India. I have already spent about 40 yrs in R&D in India. I would love to be associated with a personality like you. I will see all your lectures on you tube. I salute you for clear understanding of Physics concepts.

Hello Pf. Lewin. You are a life-changing professor. Im a spanish Physics sutdent in the UK. I want to be a teacher when I grow up. With corona, online classes got boring and unappealing. With your lectures I feel provoked to learn and think, and remind me why Im studying this degree. Furthermore, I would like to someday be able to teach in this engaging and passionate way. Thanks for everything ;) Ramon

[@laucha2709]

Im from Argentina and i course in a good public university, but when i see this video and this professor i get excited. Professor you are incredible, thank you so much.

[@sanuwarrahmanumar9670]

Love & respect for you, Prof. Walter Lewin from a Bangladeshi physics lover.

[@jmoak311]

I’m obsessed with these lectures. On my 2nd go round of 8.01 and each time it makes more sense and becomes that much more elegant.

[@lecturesbywalterlewin.they9259]

:)

[@davidmudry5622]

You say gravity is a Force and every action has an equal and opposite Force...isn't it a contradiction to say in Free Fall there is only the Force of gravity acting on a body without any equal and opposite REACTION..?

[@kritisingh1620]

Incredible I don't have words to tell how amazing it is

[@aida8263]

27:16 This is the best physics teacher I`ve ever seen, And I had a couple of great ones while in university.

[@mhmmdalwf]

Love & respect for you, Prof. Walter Lewin from a Indonesian physics lover

[@tiqlol]

i have never enjoyed a lecture this much before thank you very much sir

[@rajarammishra255]

I was amazed to see the magic of physics in this lecture. You've done such a good job sir 👍.

[@lecturesbywalterlewin.they9259]

Keep watching

[@mahendersingh6484]

Yes u r right👍

[@oussamasaidi3420]

Walter I would like to thank you for the wonderful lectures. I have watched all your lectures and my favourite lecture that I consider the most enlightening is 16 part of 8.02 about electromagnetic induction. I'm a final year electrical engineering student from canada. Cheers!

[@lecturesbywalterlewin.they9259]

yes, lecture 16 is an eye-opener EVEN for many physics teachers!

[@rajshuklarajshukla8470]

Sir u r my role model . Ur lectures truly motivates me to work on physics

[@rawadabiorm6298]

Amazing explanation. Thank You doctor Lewin.

[@samakhanjani6522]

Dear Professor, I love the way you teach, especially those experiments. I wish to be your student. Thanks a lot :)

[@SudeepJoshi22]

If I was at these lectures I would never had blinked my eye.. Love your lectures.. ❤️❤️

[@rogerdodger8813]

Teacher always made us start with Sum=ma (newton II). This is the most important line ever in any such problem!

[@gamersvalley]

No offense ! I too love his lectures but at 9:42 " string has negligible ass" and then instantly says mass , massless 😂🤣.

[@frustratedstudent5710]

😂😂😂😂😂😂😂😂🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣

[@frustratedstudent5710]

🤦🤦🤦🤦🤦😝😝😝

[@biswaranjansahu4640]

U r a good listener

[@ashwinikumar8455]

After watching ur videos I started understanding physics and now I am highly attracted towards it ..

[@davidmudry5622]

You say gravity is a Force and every action has an equal and opposite Force...isn't it a contradiction to say in Free Fall there is only the Force of gravity acting on a body without any equal and opposite REACTION..?

[@codetrooper9279]

I always end his lectures with a smile on my face

[@GenuineHuman7]

Lewin sir, this was my first time when I PRACTICALLY learned the varying cases and weightlessness ( as shown in the video ). Last year, in class 11, went through books, understood nothing. In this lecture, within less than an hour, you just made it simple and practical and UNDERSTANDABLE . Wonderful !

[@davidmudry5622]

You say gravity is a Force and every action has an equal and opposite Force...isn't it a contradiction to say in Free Fall there is only the Force of gravity acting on a body without any equal and opposite REACTION..?

[@najeebullahkhaan7512]

i will always wish to sit in your class to love the physics....Great sir

[@MsIs38]

Professor Walter Lewin, watching your videos is like watching a Sci-Fi movie. Incredible facts that I had never realized before. How amazing is how the world works! These lectures are a treasure and I´m very lucky to have discovered them. Thanks for sharing them.

[@lecturesbywalterlewin.they9259]

Wow, thanks!

[@davidmudry5622]

@@lecturesbywalterlewin.they9259 You say gravity is a Force and every action has an equal and opposite Force...isn't it a contradiction to say in Free Fall there is only the Force of gravity acting on a body without any equal and opposite REACTION..?

[@samarthsai9530]

Was Dave a student, He's really smart. And also do MIT profs have dinner with the students! If that's the case, that's how the relation between a student and a teacher should be. All your students around the world love you.

[@lecturesbywalterlewin.they9259]

David Pooley was my graduate student in 1999 when I gave these lectures. He is now a Professor in the US. He is very bright and also an outstanding teacher. He got a teaching award at MIT.

[@ranjithgowda.a9003]

Thank you for your kindness and generosity for the other side of MIT. We are blessed to have you sir. While I am desperate to this type of lectures.

[@lecturesbywalterlewin.they9259]

My pleasure

[@najeebullahkhaan7512]

love the sound the way you explain the motion of M1 and M2 🥰🥰

[@easyphysics9047]

you are the one and unique,best wishes for you

[@unknown-mq1jv]

You are my inspiration to learning physics I love your lecture... You are best professor Lewin (W.L) Sir I really want to meet you in my life....😭😭

[@boboganbobogan9297]

i don't know how to thank you for these incredible and interesting videos!!!

[@AjaySingh-um4gy]

Thanks , for replying my quest . Now these terms are quite clear to me

[@sekharandivakaran]

Fantastic lesson. A must watch all physics students.

[@hserma]

Best way to teach. Thanks professor!

[@manishvyas6791]

Very nice lecture on weight chalks are incredible

[@cste3130]

Great lecture! Explained in detail the concept of weight! Also, amazing demos!

[@lecturesbywalterlewin.they9259]

+Christos Stefanou Thank you

[@user-um9sl1kj6u]

Listening to your lectures on physics helps

[@MazDelaCerna]

Awesome work. Thanks for sharing!

[@abstractnonsense3253]

Soooooo good. Excellent lecture. Thank you.

[@RGLECTURES]

Lec just goes on another level

[@mohityadav2248]

Happy birthday Master ❤️🙏

[@thegiantone4039]

I love watching your lectures, it makes me so interested in physics

[@lecturesbywalterlewin.they9259]

+TheGiantOne good

[@MickhTV]

Thx for this wonderful content - CHEERS from Poland :)

[@rithikasubash6645]

professor u are our newton of this century

[@jeanlatour9151]

Your demonstrations rock !! I wish we had such tools at school !

[@thetessellater9163]

This is MIT, prestigious, well-funded, cream of the intelligence, etc

[@shraypandey4591]

thanx sir ur lectures r good after seeing these i got interested in physics

[@parthpawar1314]

Grt lecture sir , made concepts more clear

[@muthunanthini6259]

Very great sir....tq so much.....it helped me to take a seminar

[@priyanshu988]

Sir for sure I think physics is taught in a really bad way but now I am sure in future I will try to be a proffessor like you I am loving your lectures and these are so beautifully arranged that the concept becomes crystal clear Really I am in ❤️ with physics now

[@preyunknown1820]

dude dude prof dave is amazing give him some appreciation guys its not easy to build that thing

[@coolstar7819]

Brilliant demonstrations! Thank you so much!!

[@lecturesbywalterlewin.they9259]

Glad it was helpful!

[@manishkhanna3828]

demos are cool

[@sanjaysingh-lz7ke]

I am in class 11 preparing for NEET. Your videos helped not only me but also many aspirants. Thank you very much sir .. 👃👃👃 (from India)..

[@davidmudry5622]

You say gravity is a Force and every action has an equal and opposite Force...isn't it a contradiction to say in Free Fall there is only the Force of gravity acting on a body without any equal and opposite REACTION..?

[@surendrakverma555]

Excellent lecture of Physics. Thanks to great Physicst of world. 🙏🙏🙏

[@lecturesbywalterlewin.they9259]

It's my pleasure

[@chikoo7584]

i have not clicked on this video to learn physics but to enjoy it like an entertainment, power of true physics

[@rajaradi802]

I love his phrase "physics works"

[@harikrishnan3873]

Great teacher........ I loved his lecture. Thank you sir.

[@lecturesbywalterlewin.they9259]

You are welcome

[@aravanand9267]

Sir Your teaching style is amazing.I am now fan of you.thanks to youtube and thanks to you sir to give us these opportunity.Thanks a lot sir.This is my first public comment.please reply sir.I shall be greatful.

[@lecturesbywalterlewin.they9259]

:)

[@derhotcenplotz3464]

thank you, professor!

[@deepmalasharma5479]

Nice lectures....Thankyou sir.

[@brianrangel1885]

Just got a 95 on my first college physics using Calculus exam! Wouldn’t be possible without these lectures

[@davidmudry5622]

You say gravity is a Force and every action has an equal and opposite Force...isn't it a contradiction to say in Free Fall there is only the Force of gravity acting on a body without any equal and opposite REACTION..?

[@heyya4894]

Love from India ❤️

[@Deveshkumar-kk4od]

🙏🏾🙏🏾 koi indian to mila great

[@aceofthebrothelstreet6720]

i am just thinking . when it was recorded just curious. He is looking young . But alas one day everyone have to go. btw love u sir ,i hope u live long.

[@lecturesbywalterlewin.they9259]

recorded in 1999

[@muhammadaun5396]

@@lecturesbywalterlewin.they9259 Well, the see-saw look alike for Tension example when both are equal.. Also Now Superman in weightlessness can get extreme sickness.

[@jeniferrodriguez1463]

At minute 17:30, when you put that the acceleration is g, it would not be -g? The equation is a = (m2-m1) g / (m1 + m2) and if m1 >> m2, acceleration tends to -g?

[@ankajkumar3401]

Sir you teach fantastic

[@IAmGrubble]

Great prof. I can't help *but* point out the amazing slip just after 9:40.

[@lecturesbywalterlewin.they9259]

what's the slip? I did not noice any slip

[@Peter_1986]

+Lectures by Walter Lewin. They will make you ♥ Physics. Benjamin probably means the fact that you accidentally said "small ass". :D

[@dahawk8574]

Excellent lecture & demos! 45:16 - a couple of suggest for improvement... There is a disconnect in terminology. The slide is actually accurate when it states "2g" & "0g". It needs to be understood that pilot language is being used here, like when it is said that an F-16 is pulling 9g's. Here "g" is referring to total acceleration, meaning the acceleration due to gravity _plus_ aerodynamic acceleration forces. The acceleration scale that pilots use sets "1g" equal to the acceleration due to gravity at the Earth's surface, so that's why they use the letter "g". The disconnect in terminology here is because the same letter is being used by different people to mean different things. Prof uses it to mean accel due to gravity, whereas the slide uses it as a scale for the measured total acceleration. Another statement that needs to be addressed from that same point in the video: "The engine is restarted." I expect everyone is clear that the engines were never _stopped_ at any point during the flight. So what is really meant by "restarted" is that the thrust level is increased. During the parabola, the engine thrust level is set to only counteract aerodynamic drag. The net result of this engine thrust is such that the flight path and velocity would be as close as possible to the trajectory if it were to have happened if there was no atmosphere at all, like a spaceship would experience. During the 2g pullout, a lot more thrust is needed, so the throttles are pushed up at that point. In the big picture, my points of feedback here are minor. Overall this lecture is amazing! And it would be great if NASA were to be so clear and precise in explaining what weightlessness is and what it isn't.

[@necatigoren9187]

Dear Professor, If i take the positive directions upwards in the string problem in which there is two mass connected to the end of the the string, then in the two cases that you talk about the accelaration for m1=0 will be positive. Where do you think i did something wrong?

[@janarias5427]

Hello professor Lewin, I wanted to thank you for all the effort and passion that you put in every class you taught, it definitely make everyone to love physics. I like the way you presented perceived gravity in the rotating space station and some concerns have emerged on me regarding U.C.M. In the example of 26:19 , i can’t understand how is that gravity doesn’t affect the magnitud of the tangential velocity. I mean i know is rotating at a constant speed, but if you do a free body diagram of the mass at the rightmost position, the gravitational force should affect the speed and make it smaller. So i’ve been thinking about this and i could’t give an answer to myself. How is that gravity doesn’t affect the magnitude of velocity? How is that the ball keep a constant speed? Or my analysis of the free body diagram was wrong? I hope you can read this and give me a hand to make this more clear to me. Thank you for everything you have done to all students around the globe. Greetings from Perú.

[@studywithunderstanding7153]

Really Sir you are great

[@rainbowsource6385]

Beautiful lecture!

[@lecturesbywalterlewin.they9259]

Glad you liked it!

[@Serra_El_Shorbagy]

You're amazing♥️⚜

[@georgemathew8218]

Very Good Explanation Sir. @

[@Gabrielr8]

Would be so cool if i could time travel and see Dr Walter in his very early days at MIT. Wonder what was it like then.

[@NancyHernandez-jo3xl]

I enjoy everything about physics especially the simple algebra at 15:00 that is used. I got lost though how was the a for acceleration isolated to provide the new equation of a=msub2-msub1/msub1+msub2 g?

[@amuzemuse6812]

U r God...respect u a lot

[@aimerphysics-haroonsir9668]

Love you so much sir

[@faheem4581]

A small question, how do you judge the time of impact after jumping off the table and landing?

[@subbiahmarimurugan1039]

31: 045 to 31:05 exactly half a second..!.. exellent!!

[@sriram.v.s5337]

Sir at 41:26, I think that the 45 degrees is for maximum horizontal range of the projectile because the range is given by u^2sin2(theta)/g

[@107-amaanrangrej7]

Yes

[@bhend1]

Why do you even want Maximum Horizontal Range? We want Maximum time of flight!

[@muhammadshafiq17]

Excellent ...100%