Lec 24 | 8.01 Physics I: Classical Mechanics, Fall 1999

[SuperMrBentley]

In soviet russia lecture takes you.

[Elzelgator]

i could not understand why it is stopping

[Kricardose]

I am very happy to see the vidoe Rolling Motion Gyroscopes VERY NON-INTUITIVE after you give this

[bebeheuy]

Good, I like that you share this video Rolling Motion Gyroscopes VERY NON-INTUITIVE, I wish success always

[Mjhond]

Steady I Really Like This Video Rolling Motion Gyroscopes VERY NON-INTUITIVE

[chrlsnewsom5]

This is a "habitual" video. =p

[timothymanzella]

Your video is a favorite on Astana

[perepe10]

By now this is my favourite lecture by far! now I understand why cycles and tops don't fall!

[RockandRollFantasy]

Professor Lewin appears numerous times in Brian Green's "Fabric of the Cosmos" series' episode "Quantum Leap." I Googled him bc of his infectious enthusiasm for the completely counter-intuitive rules that govern the sub-atomic world. As a completely non-math Philosophy major, I deeply appreciate his conceptual/visual approach to the material and recommend Greene's episode(s) to your thinking non-egghead friends who you may want to include on your journey to understanding.

[RoryNguyetxi938]

najo ich bin total naja wie soll ich sagen reich

[EDWINSHELLY]

I would like to be the diciple of this teacher..god bless him,he's simply amazing..

[EDWINSHELLY]

I would like to be the diciple of this teacher..god bless him

[violetmoonster]

I love this prof.

[Elzelgator]

PLEASE SOMEONE HELP...

1)Can object with a constant acceleration reverse its direction of travel??

2)can it reverse it twice?

PLEASE I NEED ANSWER TODAY....

ıf any one see this comment help me....

[AlanKey86]

@Elzelgator This is a good question.

The answer to 1 is yes. If its velocity were 10m/s and its acceleration were -1m/s/s it would begin travelling forwards, decelerate, then start travelling backwards.

THe answer to 2 is no.

[alexrodsn]

He is awesome! That's because of people like him, I love mechanics. This kind of stuff inspire me to study a PhD in MechE.

[Nshuti57109]

Thank you so much you've made my night :))

GBU

[CGsportsvideo]

At 44:00 Inertial Guidance systems for boats or planes...or your Nintendo Wii remote.

[CGsportsvideo]

This explanation turns awesome at the 22:30 mark.

[sleezyveazie]

I got it right! There was no winner or loser!

[BiLlyBoByeah]

Thanks so much, exam in a week and a half and your way of explaining gyroscopic motion has finally made me click. This kind of teaching inspires students, I wish our lecturers in London could be that clear.

[Garyyx24]

you lost me after the 1st minute

[SabelineBarzilla]

WATCH'.;THE;',FULL,`;TV;.,SHOW­;.;ONLINE,.'

ＷＷＷ.ＳＴＲＥＡＭＴＶＲ９Ｘ.ＴＫ

GO`.;TO`'`THE,`.URL,`,

[Saubande1981]

47:47 I really don't get the idea why the angular momentum vector is pointing in his(!) direction!

please help!!

[permatroll]

@Saubande1981 you can't fix stupid

[Saubande1981]

@permatroll rather than insulting me, you could try to explain the problem, to give a proof of your intelligence!

[Diemedes]

@Saubande1981

A practical way of finding the direction of angular momentum is by using the right hand corkscrew rule; simply use your right hand and close your four fingers in the direction that the object is rotating. Your protruding thumb then shows you what the direction of the angular momentum is.

[Saubande1981]

@Diemedes Hi! thanks for your answer! Actually, that's the rule I used to apply too, but as how you see from "our" direction (camera position) the wheel is spinning counterclockwise , so by the right hand rule, the angular momentum should be in our direction, no? (isn't it? - maybe its just an mistake of perception)

I'm confused by what he says at 47.45: "The wheel is moving in this direction" and at the same time he describes a counterclockwise movement?!

[ThatLuckieDuckie]

Why am I watching this, I'm 13. Ahaha. He's making me feel real dumb, I have absolutely no Idea what he is going on about, but he is very bery clever. I'm just finding it funny listening to him, and now I am tapping 1, 2, 3, 4, 5, 6, 7, 8 and 9 in quick succesion. Actually I understand a few of the words he said, such as Radius. Haha.

[EducationForDummys]

question: "nature is very clever... sum of the force is zero", so are you indicating that the object only falls when there is no torque present of the fly wheel? or are you indicating that force does not matter in terms of the wheel falling down when the wheel is not spinning? because the mg force and the tension force are always there. Since the angular momentum is not chasing the mg torque (no spin), the fly wheel position does not change, hence the wheel mg force can be applied successfully?

[Quinzio]

wow, watching this for me is better than any hollywood movie

[HEKOT77]

Great!

I remember professor Tatur from Moscow Institute of Engineering Physics and his assistant Boris Ivanovich. The precession of Boris Ivanovich was an amazing show!

Thank you, Sir.

[cropsey7]

Bravo Maestro!!

[cod007skilldfan]

Where's the weel chair and microsoft sam?

[carreraGT92]

Um why is there no applause at the end? If we had this lecturer at my uni there would be a standing ovation, fantastic lecturer

[Nabo00o]

I have a question for anyone who would like to help. I guess many of you have seen the demonstration by Eric Laithwaite where a rotating wheel on a long shaft is lifted.

There will be exerted a precession force which supposedly forces the wheel's angular velocity towards the torque exerted.

Okey, but what happens if you place another wheel close to the same wheel, but spinning in opposite direction?

Since the two precessional forces goes in opposite directions, will there be no total precession?

[Nabo00o]

So to sum it up: One shaft with two wheels at the same end, spinning in opposite directions.

If there is no total precessional movement, will there also not be any opposition towards the torque exerted on the shaft??? Or will the there be an opposition but no movement?

Anyone?

Thanks!

[HunterDX77M]

The demonstrations really helped. I was so lost with all the equations flying everywhere.

[jens009]

Watching just this lecture has given me a better understanding of how gyroscopes precess. Great lecture and demonstrations!

[coolweather100]

Professor Lewin, you are awesome

[Vaizard52]

such a good teacher

[4kx]

I dont understand only one think. in 5:22 he is showing as "a=W (dot on the top) * R" ...

What is doing that "dot" above the W (omega)??

[bobenhuizen]

@4kx The dot above w shows it's the derivative of w (w = angular velocity).

The derivative of velocity (with respect to time) gives acceleration.

In other words... dw/dt = w (dot) = alpha => angular acceleration.

[4kx]

I love phisic ^^

[MajudaMusic]

very non-intuitive.

[samuel91222]

my favourite lecture!

[lep1950]

Precession: The economy before 2008

[alquiora]

I wish I had such teacher at UNSW... 

[Sk82beast]

You don't have to know this for Physics B, but for C you better have damn good understanding

[GetMeThere1]

I see the makings of a good bar bet here :)

[iKangaroorat]

So this is how we are going to stear our fly cars?

[ivooooooto]

Ok, this gay hi wants to drop dust in our eyes with that lection for kids.

that gyro effect the military they use for antigravity and lection like that full with stupid explonations just ..... brain wash to be not study in a deep

[Ubermeisterpingvinac]

this guy is so pro

[miramar4life]

i believe that the reason for the hollow tube to be slower than the solid tube is because of air resistance....if they were first placed in a vacuum and then let go they would reach the bottom at the same time....anyway, overall great presentation

[darkoriginhunter]

@miramar4life If that were true, then why doesn't a larger solid cylinder of the same mass as a smaller solid cylinder go slower?

[Gintable]

@darkoriginhunter Because the mass and radius "cancel out" of the equation. Only the ratio of rotational inertia to maximum possible rotational inertia matters...i.e. the leading constant of the I = #*m*r^2.

[mohankk2002]

@miramar4life, the reason behind the difference in time is due to difference in their MOMENT oF INERTIA , as torque = I * alpha

[swade211]

@miramar4life

did you listen to the lecture? it has nothing to do with air resistance

[miramar4life]

his question did not have to do with the lecture to begin with....thats y he left it as an open ended answer

[Squatchmichael]

No. It' the moment of inertia. You can work it out. He just did. The acceleration differs by 1/2 for the hollow cylinder, versus 2/3 for the solid. You JUST saw it--nowhere in the derivation was air resistance included.

[Nabo00o]

Hmmmm....

I don't think spin is compatible with total momentum conservation. What happens if you apply a linear force to accelerate a wheel?

The wheel spins and you are pushed back with the wheel....

[1freedomfighter11]

wow that is sooooooooooo cool.

[SkumBanana]

Is anyone able to explain me 23:05 in terms of conservation of angular momentum? As I understand your initial L is the one from the spinning wheel (vector parallel to the ground). Considering the system wheel+professor+stool the torque applied is internal so we must have conservation. But I don't see why the professor's+stool's spinning is going to do it...

[gaucable]

if you had known nothing about this you would bet anything that this kind of thing is not possible.... gyroscope is like Chuck Norris, when he does pushup, he isnt lifting himself up, hes pushing the Earth down. You just wouldn't belive, it's really super non-intuitive

[em84009]

Very non-intuitive is the aceleration increase when we put mass on the system! More weight needs more power so it's like energy coming from nothing...

[Dweirdo12]

16:00 to 17:00 made my mind explode :<

[JonThm]

Oxford can do nuclear fusion from a H plasma.

[Ogaitnas900]

lmao 26:44 "Cross product: making smart people look dumb since 1773"

[gomunkul]

@Ogaitnas900 why 1773? :)

It's a recent invention, late 19 century if I remember correctly.

[Ogaitnas900]

@gomunkul

wikipedia says "In 1773, Joseph Louis Lagrange introduced the component form of both the dot and cross products in order to study the tetrahedron in three dimensions"

so I guess the number stuck, but yeah, late 19th century too "The cross notation, which began with Gibbs, inspired the name "cross product". Originally it appeared in privately published notes for his students in 1881 as Elements of Vector Analysis"

[zopilote1986]

His explanation that the wheel doesn't drop bc the net force was zero seemed strange because if you drew a similar diagram with a rod attached to a string and opposing forces at each end, the net force would not be balanced. It seems a better explanation would be that the mg force downward on the wheel is "translated" (via torque) into the rotational movement rather than downward. As the angular momentum slows, less is translated into rotation and gradually more into downward motion.

[dizzib]

@zopilote1986 google 'feynman gyroscope diagram' for an alternative explanation

[pudicio]

No, I'm not 'postulating' such a thing. Don't put your big words in my mouth.

A londoner living in India will still speak english.

I moved to my current residence (Delft) a few years back and the accent of my hometown is totally gone. The same thing happened to the majority of students I know.

But I'm sure you're a linguist and have hard proof to back up your claims.

[pudicio]

Being Dutch myself I dislike the accent most of us have, yes. In my comment I merely expressed my amazement over the fact that after that 40(!!!) years of lecturing his Dutch accent was still there. He probably spoke english for the majority of his life! But apparantly this view is worth 7 downvotes...

[b00n707]

I said it, because it gets very intuitive when you're defining the deviating moments. After defining this you can show, that if an acceleration (force) acts on the axis, then a deviative force (radialforces are no longer zeroing itself) acts on the axis to and the rigid body gets accelerated in this direction.

And the image of an bicycle also helps to understand why the rigid body is not falling like a pendulum. Mfg

[discoinfern0]

OMG 40:43 classic quote from Prof. Lewin.

" And now, through friction of course, all this fun ultimately comes to a halt"

classic

[discoinfern0]

lol 3:20

great professor.

Thank you MIT

[FlyingGrimReaper]

Wish they had those demonstrations for my stability and control at Georgia Tech. I would have understood how the ISS and satellites worked.

[floppydrive42]

gah MIT has such well funded classes

[CwbySpikeSpiegel]

Please tell UM to teach like you guys :-D

[b00n707]

I find it very intuitive, because if you superposition the velocity vector of a mass element of the spinning wheel with the velocity vector of the applied torque will give the mass element, if the wheel would accelerate from rest, the result will be a velocity vector which is neither in the plane of the original spin, nor in the plane of the applied spin. If you think that the wheel had to rotate in both directions simultaniously, this would not be true with all mass elements of the wheel.

[xeronegamefaqs]

great use of blackboard.

[ishaanbhola1991]

this is really amazing ...thank you so much mit...i am speechless....this is the d most noble act...

[iuliansid]

physisc`s amazing ! too bad not all countryes have all these money to invest in education.. good teachers, things to work with on experiments etc.

[Mhorix]

it is not the country that invests in education. its the rich parents of the ppl that go there.

[pudicio]

wow, this guy got to MIT in 1966, and he still has his terrible dutch accent!

[b0b2805]

great teacher! Wish we had such teachers in Delft!

[pudicio]

I hear you. Most of my lecturers in Delft can't speak proper english...

[1981walter]

Heb je ooit een Amerikaan of Engelsman die al lang in Nederland woont Nederlands horen praten? Alsof die accentloos praat.....

[Broodsnijplank]

He is so dutch xD

[psnoob]

@ 13:44 : JA! :P

[Broodsnijplank]

xD idd

[frenkydee]

hehe.. 100% sure that that professor is a Dutch guy!

[Ro3ch1985]

haha yeah, was just thinking the same thing :D you can always spot a dutchy talking english :P haha

[paragonparadox]

how did he do the dotted chalk thing O.O

[MajudaMusic]

@paragonparadox its torque - not chalk :)

[elementary69]

It is a very good lecture

[PhuqueU]

They drag out something so simple, in attempt to make it look so complicated, to give you the illusion you're smart, so you don't notice the effects of the fluoride.

[auroravinod]

learning pure rolling is not different than what i teach in my class.One has to think different cases to explain pure rolling in better way.Too much mathematical equations can never serve the purpose

[zomgmoose]

Wow... I just learned this stuff in my AP Physics II class...

:P

[savata71]

Ha! Subtitles - this is very good and usefull for foreigners like me! Now I can check any word with dictionary.

[MartinTheNext]

this is cool i wish we had such lectures

[devildogmre]

Nice class.

[summerday44]

well the talented mathematicians dont think cross product is absurd because they found som interestine things that it sghhares with other stuff i didnt learn yet. i was not appropriate to say absurd jut because its not commucative etc.

[summerday44]

intituition is the most dangerous thing, becaiuse it has no proof but mind force you to assume it, but if a proof is intituitive then it mustbe a genious

[derrynator]

so is that what happens when you spin a coin on the spot how it swivels?

[MTEXX2]

thanks MIT =D

[joemania12]

nice demos

[VelliSide]

god damn 50 fucking minutes of this shit?

[George21T]

not shit its learning .

[de5t1ny]

What is that machine call that he use to make the wheel spin

[gnihtyrevEnoitseuQ]

It's just a motor.

[savata71]

After this lecture watch video "Space bike BG 2" on YouTube.

[mitsubishi1975]

this guyz is a legend

[LTF85199]

wow, what an interesting lecture, in my state university they hire international Phd profs with horrible accent "talking" theory all day. i hear nothing but Chinese during most lectures :( Thanks MIT.

[summerday44]

ha ha hey but whn he sid nature is clever, i think its the gifted guy who came up wth the theory i cant figure out weather crosss product came before this or cross product came after to explain this. because the way cross product behave is absurd when you look at it without physics

[slippyfists]

tha boyz were soo much kewter back in 99

[PlanshB]

Thank you so much for this video! It really helped me to understand all of this.

[Animeabe]

That was really interesting.

[coantte]

That man should win a guines making a dotted line man! I thought that was some type of instrument he was using to make them. but that strait bruce lee reflexes now that i think about it he would be a perfect martial artist physics+catlikereflex=kickass

[ertrzymiks]

ownage ! this guy rox

[jessehypno]

awesome!

[lorupa]

he is sooooo good, even though I'm from poland and my english is not what I could call excellent, I understood more form 5 minutes of the film than from one hour of physics with my proffesor... I should kindnap him and take to my school.. (or go to MIT)

[RUBIMSTEIN01]

This professor should get a kinda nobel of teaching...he is a devoted professional!! all of his courses are amazing at all!!

[ranbonfil]

wow amazing professor! great video btw

[danz409]

wha collage courses online! sweet! i can learn before going and know a shitload before i go :D

[Coeli7539121]

hes really quick at drawing dotted lines =]

[albetalo94]

yes ,it is good, but i'm italian and i never understand because i can't ear and speak english very fast!!!!

[TehZelda]

this guy is so much better than my professor!

[sebastas2]

Amazing class, I always wanted to understand how Gyros work. 5/5 right away!!

[TommeyLeeReed]

I like this, my Patented engine design is a advanced rotary engine that spins in circles.

[danthemango]

holy cro, the best lesson I've ever had.

[sourabhmib]

"gyroscope" one of the toughest topic of physic.....

becomes very simple........see this video.....

[sourabhmib]

wat a teacher .............amazing......

[SpoolDonkey]

35:50 ''someone is going to get hit in the face with a bicycle wheel'' - WOW!

*goes to get string and wheel*

[shanebieda]

This guy needs to learn how to teach!!!

ah!!!

it drives me crazy!

you draw, than turn around, make sure the students see wat the heck your scribbling on the board and then you explain.

Hope he's not my teacher

oh... and this was very intiresting

[SpoolDonkey]

well, at least with one click of the mouse you can have him repeat it as many times as you want :)

[Jays0n54]

well i hope you are not judging with no previous knowledge like the ones the students have

[friendlyboys09]

heheheheh

[PAPERSCHOOL]

this is very interesting

[TSPfan]

Haha, this is definetly a dutch teatcher!! They just can't hide it :D. But it's very interesting!

[drMerkwuerdigliebe]

what? vq != vc (in global system)

vq = w*R (of course), but vc of a point (lets say P) on the circle (as it is shown on the blackboard) depends on the angle. vc = 0 when the point P has contact with ground then. And 2Rw at the opposite.

[drMerkwuerdigliebe]

...I know what he wants to say. But his draft is at least confusing. He puts two velocities of two different coordinate systems in one draft.

[drMerkwuerdigliebe]

very nice lecture anyhow. I guess I'm just used to another way of drafting forces, torque, velocity etc.

[cerealkillerds02]

There's nothing wrong with how he wrote it. If you think only about the top of the circle, it only makes sense that it moves with the same speed as the center. All the other points on the circle must move at that same speed, since the circle does not deform.

[drMerkwuerdigliebe]

no - without slip the top is twice as fast as the center.

perhaps you will confirm: the point that has contact with the ground has no velocity at all. vp = 0

Because if it has any horizontal component of velocity it would be "faster" than the ground ->slack.

and this peticular point in contact with the ground at the actual time T: had! vertical velocity downward -deltaT ago and it will have! vert. vel. upwards in +deltaT (for deltaT -> 0 (sec). => vp,vertical(T)=0

Not easy to explain that way.

[Poofyponcho]

Knowing that doesn't get you paid. LEARN SOMETHING THAT WILL MAKE YOU MONEY!!

[drMerkwuerdigliebe]

why do you watch this lecture then? knowing such stuff can make you money by the way.

but what do you propose then? What is your profession?

[Poofyponcho]

I am a Courtesy Clerk at the SuperMarket!

[drMerkwuerdigliebe]

Aha - and now you are looking for an assistant?

Come on. It's O.K. I'll shut up.

[Poofyponcho]

Hahhaa. I was just kidding to begin with :D. Wanted a reaction :D hehe

[drMerkwuerdigliebe]

:\ - begin with?

[Poofyponcho]

Yeah. As in, my initial remark was a joke. :D

[spitgalore]

Now I understand how gyroscopes work.  He explained this so well, thanks for sharing.

[Fragneck]

Is that a Dutch teacher? His dialect sounds like mine...

[DominicC13]

Yup, he's Dutch.

[iHeartHandJob]

i fail

[oSaTeXo]

awesome <3 physicks =)

[yoursallen]

very well explained!

[a009480191]

Nice Job, Similar to Koskelo's Lecture at Skyline College, CA

[kimtso21]

great job