My great regret is to have not studied physics as well as iI want to do do now, when i was in my 20 and when I got a physics graduation in Italy....Now I am 40 and thanks to you and to David Jerison I am taking some books in my hands, once again
@@lecturesbywalterlewin.they9259 So, because the centre of the hollow sphere has zero g because of symmetry and there is no mass in the void, then the divergence is zero in the void which means that g doesn't diverge from zero❔
@@The_Green_Man_OAP For sure ! I am just getting started with advanced math (not really good at math XD) and these things make me even more uncertain 😨. Oh well, the only cure for uncertainty is practice✊
@@The_Green_Man_OAP > *there is no gravitational field anywhere in the hollow sphere as long as the thickness of the shell is the same.* To place 3500 kg somewhere inside the hollow sphere does not change that as the gravitational field due to 3500 kg mass is *completely negligble.*
Love you proff. And really appreciate that you are still uploading... I used to watch your physics lecture during my highschool days...it's your videos that made me love physics... And I am going to pursue physics for my masters degree this fall...❤❤
Pretty easy question. In reality though there would be gravitational waves flowing through the sphere from all over the universe. It does make me think about the isolation that could be achieved at Lagrange points if we were to put this hollow sphere there and then run tests within it we could probably get more precision from the instruments and who knows maybe decode alien messages sent through gravitational waves :D
Sir I Have just recently found your channel. I'm from India and studying in class X. And I have been preparing for Jee from class VIII. I have completed XI maths syllabus. Now for physics I'm going to continue with your channel. Thank you.
Sir im huge dan of yours and astrophysicist Neil degrasse Tyson....sir u also pls make some videos like him to get people interested in physics..... Infact uve made greater discoveries like rotating neutron star,bursting pulsar,etc
My goodness! I'm there in 2:47.😊 You helped me love physics, Professor. I was a winner in the national physics olympiad of Bangladesh this year. Your lectures helped my journey through physics. That still goes on. Stay happy. "We'll be friends".❤
Professor. Do you have an opinion on the witch hunt trial against Trump verdict today? Keeping in mind we physicists' are logical thinkers. However there is nothing wrong with thinking out of the box.
Nice see TGM up there 😊. The density is that of a white dwarf btw. Neutron Star ▫️ density is 10¹⁸ kg/m³ (for ▫️=2×☀️), therefore this sphere is nowhere near a Stellar BH ▪️. In this case the hollow sphere ⚽ density is about 84×10⁶ g/cm³ which makes it a WHITE DWARF ⚪ (wrt it's density). Solar mass is M(☀️)= 2*10³⁰ kg. => For neutron star: M(▫️)~1.5 to 2M(☀️), R=10⁴ m => ρ(▫️)~(3/π)*10³⁰/10¹² ~ 10¹⁸ kg/m³. For a BH: Circumference of BH =K(event horizon) =4πGM/c² Officially, it doesn't have a real radius b/c of the singularity breaking "space-time". But if you were to ignore that, the radius would be: R= 2GM/c² For M=3M(☀️), this is: R=3*40.02/9*10⁹=13.34 /10⁹ [m] About 133.4 × atomic size.
Sir can I ask you something ?? I'm in 12th grade and I am preparing for IIT jee exam and my favourite subject is Physics. But my physics approach is not that good. I genuinely love physics and want to be an astrophysicist. Can you please tell how to learn physics so that I can fulfill my dream 😢😢😢. Sir if you see my comment please answer it and thank you for your other noble work🙏🙏🙏. You are the best physics teacher in the world 💕💕💕
But are we sure that the inside of a hollow sphere (with a core as dense as a black hole) would still have zero gravity? I mean, the textbook, as I remember, used Newtonian gravity and not general relativity to demonstrate the 'zero-G' zone inside the sphere.
any mass inside the hollow sphere will cause a grav field. Read my solutions. A bh inside is a nice joke, what would be its mass and what would be the radius of its event horizon. Plse do your homework first!!!
Hello my dear professor...I am your big fan I watched all of your lectures of 801amd 2 ....dear sir it is very humble request I want a small video podcast with you. It will be a great hounur for me. Kindly must reply could you give some of your valuable time to your this fan....big fan from Pakistan
With the observation of the Shapiro delay we know that it takes light longer to traverse a path grazing a mass. In General relativity we explain that with curved spacetime, but in the end it makes no difference with light slowing down. When we come closer to a Black Hole, BH, then the Shapiro delay will grow. A light path reaching the BH Event Horizon, EH, then this delay will grow to infinity. In other words the light will not progress any more. Because nothing cn surpass the speed of light also matter will follow this delay. Thus all matter will slow down near the EH and settle down as a condensate on the surface of the EH and nothing ever will traverse that boundary further inward.
Irwin Shapiro is a friend of mine. He is now 94 yr old. He was a colleague of mine at MIT. He moved to Harvard and became the director of Astrophysics. I was 3 years on the visiting committee.
Sir, I am hailing from India... here, as you may know, we have to appear in 2 exams namely Jee mains (qualifier) and Jee advanced(2nd level). I am in 11th grade and I will be able to appear for these exams once I finish my 12th grade. I have started preparing for Jee and joined a coaching, where only selected students are permitted to be in it on basis of their past meticulous performances on national level,, and their aim is to get us under 1000 national rank.. I am seriously not going through their expectations well, but my roomate and friend( i live in a hostel) is a very bright studemt who is topping every subject and scoring great marks in tests which can easily earn him top 50 national rank. His dream college is MIT and wants to graduate from there, but he is not fluent in english. Also, he wants to pursue his ambition so can u please guide him how to improve in english and what to do to get admission in MIT as a foreign student... PS: I know it seems foolish to ask you, as we can easily find it out online, but I would better like to take the advice from you and I would love if you oblige us by giving a tiny bit of career advice which may help forever.... Sorry about the comment being too long...
Atmospheric pressure is about 100 kPa. The difference in pressure per meter of water height is 9.8 kPa, given by deltaP = rho*g*h. If you can make a 50 kPa vacuum below atmospheric pressure, then you can suck water up by 5 meters. The water pressure will be 100 kPa at the bottom, and 50 kPa at the top. The theoretical upper limit is about 10.3 meters, if you could produce a perfect vacuum at the top. The real challenge: most trees you see are a lot taller than 10 meters, so how can a tree suck water up from its roots? The answer surprised me.
@@lecturesbywalterlewin.they9259 There is Physics in JEE Advanced exam. If you solved those problems you would obviously then teach physics, because someone would definetely learn something new.
Wilt u misschien aub iets zeggen over de genocide in Palestine-Gaza via uw RU-vid channel? Ik weet dat het alleen voor natuurkunde is, maar Ik hoop dat de wetenschappers iets van hun tijd geven om te staat tegen doodmaken van mensen! (Uiteindelijk natuurkunde is ook van en voor mensen leven)
@@KeithandBridgetI posted a comment about the what kind of object this can be compared to but I think WL has held it for review. Here's the short version: White Dwarf.
@@The_Green_Man_OAP I saw that comment. I'm glad my throwaway remark has generated a bit of a discussion. Even WL's simple problems take my thoughts in strange directions. Oh, and I am not a professional physics teacher or astronomer.
@@KeithandBridget When someone explains physics problems to us and does a good job, he is our physics teacher. Thank you, Keith. Maybe I'm only nineteen and haven't seen a monkey who can write Shakespeare. It seems that you are very excellent. Have a nice day.
Hi professor We study subjects like science, commerce humanities arts I want to know how many areas of knowledge are there in total Atleast a rough figures Not in detail In how many parts universities divide entire known human knowledge If anyone else reading this beside professor He can also answer this Thanks for reading
Hi Professor Lewin, I'm Saptarshi from India, currently in the 10th standard. I wrote a paper on Relativity for my school magazine which I wanna share with you. Could you pls give me your official contact details?
Internet you are watching from Those services are provided by India itself So don’t use internet Go to Pakistan See for yourself What they have Ungrateful bastards,,,,,full Hindu rashtra
