Lec 8 | 8.01 Physics I: Classical Mechanics, Fall 1999

[dqds]

At 3:33, why is the angle between the green lines and the pink line mg equal to alpha as well?

I know this is a hs problem but would be nice if someone explained.

[nickstout513]

This is a very "rightful" video. =p

[strike325]

this is the worst song ever.

[TheHedgehogPilot]

Salute to MIT for recording all these lectures, I am in 9th grade preparing for IIT-JEE 2015, and I find these lectures very informative and straight forward. Today only I discovered this channel and related videos and I hope in future, they will make my concepts as clear as crystal. Respect to Professor

[93tap]

LIFE SAVER!

[o2FRESH4u]

i dont know what this is but i watched it for 42mins and enjoyed every2nd

[prajakta2871995]

I love the way he teaches this . he is a great teacher .

[TomPark1986]

The prof is so clear in his explanation. Amazing.

[anakmudajaman]

I Love The Video Friction It Can Increase My Knowledge

[AntoMelta]

Good, I like that you share this video, I wish success always Friction

[willamricard]

Nice Video Friction That You Share , So Very Nice Thanks You

[imegatrone]

I Really Like The Video Friction View the complete course From Your

[bundawartini]

Your Video Is Very Useful Sharing

[WizkidKumar]

Thumbs up if you are the #250,902 viewer

[s0cialnetwork]

OMG!!! Hi i am in 8th grade in bulgaria and we learned this before a couple of months, we even learned kinetik and potential energy

[victorefamiliadmais]

im brazilian and i have 15, i learned this with 14 O.o

[theChannelofMe]

10:15

[zon723]

@ifsp0321 we studied that in school too ..and we're studying it again in uni but more complicated and detailed ..

[MrClosercloser]

@zon723 true mate.It's clearly that that guy haven't studied at uni/college :)

[ScorpiaX]

Is this an introductory/refresher class? Everything in this lecture, I did in my HS for the december exam atm.

[tayyabnaseer1]

This is a great teacher of physics

[zacherycote49]

This video went viral on Prague

[xiuqin24]

Teachers in Singapore always have to shout . These types of mics should be given to teachers to aid them when they teach .

See ! Teachers rely SO MUCH on their precious throat in imparting knowledge to you all . Therefore ! Let ' s all give all the TEACHERS in this world a WHOLE ROUND OF APPLAUSE with thumbs up to keep them GOING with POWER !!!!!!!

[Taenaglar]

I hope these students at least appreciated that they had one of the best physics professor of all time.

[D4rkFoX94]

I learned this with 12 years old

[boogiebuddy01]

just within the first few seconds of watching this video I can tell this guy is a great teacher. I have never seen any of his other classes but I can just tell that he knows exactly what he is talking about and he doesn't beat around the bush about it. He puts the facts into understandable basic elements that are related directly to everyday experience. Wish I had teachers like this in school.

[legend519]

wtf, they are teaching this at MIT? This is the kind of stuff we did in grade 11...

[Ghaiyst]

@legend519 It gets more complicated. But they have to constantly reintroduce the ideas to make sense of the "college leveled" stuff. you know?

[nadal0709]

@Ghaiyst are u MIT student?

[Ghaiyst]

@nadal0709 I wish. But I was talking about college in general.

[Devotio]

Walter Lewin's presentation is extremely elegant, precise and simply masterful. Look at that blackboard @4:20! Teachers of this quality are rare gifts.

[yosoet77]

Hi guys,

I'm studying electrical engineering in the Technical University of Munich and

i want to spend one semester in the MIT. The problem is that i don't know any exchange programms offered in my university with the MIT. An other thing, i ve been told that i need to find a Student form MIT who wants to spend one Semester in my university too, so that i can make an excahnge.

Can you help me or do u have some useful links for exchange programms of the MIT.

Thanks a lot :)

[enniodoriss]

I WANT THOSE PIECES OF PLASTER

[LanRous]

he makes me really really like physics

[BrothersImageGroup]

In russia we was learning that during the kinder garden...

[greatcebu]

wtf..the only thing i know is the chalk he is using..

[bobbyfearfactor]

What's the answer to the question he posed at 11:28?

[kjplive]

@bobbyfearfactor Why race cars have wide tires? For increased traction (friction) on the track. The way he words it he seems to think the size of a tire doesn't matter but that is not true. A formula 1 car cannot transmit 600hp to the track with bicycle tires, the cars NEED wide tires. The scientific reason for this not following his rules of friction is beyond me. I would imagine it has something to do with the turning motion of the tire (powered by the engine) that makes his example different.

[kjplive]

@bobbyfearfactor The reason for wider tires isn't that the increased contact area leads to more friction. The design parameter that determines the coefficient of friction between the tires and the track is something related to the molecular compressibility of the rubber, the softer the rubber, the better the friction. However, when you use a softer rubber, you need to make the tires wide enough to give them strength. So, the softer the tire, the wider it needs to be, to withstand design forces.

[owaisoz]

but awesome ! (y)

[owaisoz]

is he dying or somthing ? lol

[cobolt13]

How did i end up here. Lol

[Gytax0]

@cobolt13 It's a good place to start.

[Thebuterflygurl]

cud sumone explain tht flea circus..??? :O

[TookMe20min2findThis]

@Thebuterflygurl

It is simply to demonstrate that with very little friction, it takes only a minute force (the force of a flea for example) to get any object moving.

In fact, it similar as pushing any object in space when there is no air friction or gravity. Any force applied to an object (say in equilibrium, that is not moving) will make it move.

[astinmartindriver]

Thank you! Excellent video... 

[TweFoji]

501 never get laid

[Gytax0]

@TweFoji What an idiot.

[TweFoji]

@Gytax0

uppppss =P

[feeltheillinois]

holy crap he can draw really straight lines freehand

[lfsp0321]

In Brazil, we learn this in school.. for real

[mrlmitbib]

@lfsp0321

said: "In brazil, we learn this in school... for real"

We learn this in school in Australia, for real... lol... so do students in china and most other countries above the poverty line...

and i am sure even some schools in countries below the poverty line...

just saying don't feel special.

[arestes]

@mrlmitbib that is true

[iamreadingboobs]

@mrlmitbib A country is poor or rich depends on the government in our country(Vietnam)high school students have to learn a lot and have to win over a lot of students in order to attend university(some of our university has 6 or 8% acceptance rate).After they pass the arduous exam,the knowledge they were taught is only theory and don't have practical use.So in the end,60% of our grads don't have a job relevant to their major.So if you are luckier than us students,then don't waste it.

[Cedna]

@lfsp0321 And that is the reason why our students go out from college with less knowledge than they had before. Our teaching system is a failure. In the U.S. they only learn this in college and still make the best engineers.

We should not feel special.

[arestes]

@Cedna what? EVERY physics/engineering department in the world has an introductory course like this covering the same basics that students have seen in highschool. Americans, peruvians, indians, brazilians... they all see (not very in depth) this stuff in highschool and later on they review it in their first class of physics... this says nnothing about the teaching system of anyone. Also, this is a quite good introductory lecture.

[mistyfields]

@lfsp0321 This is Physics I. It is normal in any engineering school, for example, restart what has been learned in high school. When I did my Mechanical Engineering course, I had these classes and, believe me, that's just the beginning. The teacher began with the same thing we learned in high school and deepened the subject thereafter.

[TheBustyGamer]

@lfsp0321 Isn't university school?

[arseniyonline1234555]

@lfsp0321 that's all very well! at what age do they teach you guys to shoot a judge few dozen of times in the chest?

[RIEKSONE]

@lfsp0321

too bad brazil has nothing to show for it

[looklookerlooking]

This guy reminds me of my favorite professor at UofH.

[TheSeph6]

teamwork,bullshit

[Vladmeister77]

41:12 ...Just epic xD :P

[wait4thedr0p]

WAYYY better than my physics professor. Incredibly helpful

[martmelee]

damn, i love math, but i hate physics... i just hate it.

[10HOME10]

@martmelee the exact opposite is my case and i think the majority is with me!! lol

[EvnThisOneIsTakenNow]

@10HOME10 not sure about that..but you sure are on an advantage on this video

[10HOME10]

@EvnThisOneIsTakenNow yeah.. i actually enjoy this stuff alot... but maths always drags me down!! 

[ZergKnightz]

My physic teacher is the old guy from the movie Up

[RE4Ex2]

i wish i studied there :(

[1683clifton]

plZ tell me fwl (alse walter louie) tats all i hear

1:13

[Damstraight68]

he can draw straight lines.. woah

[kjeksy]

he sounds like he's from the netherlands xD

[803950]

@kjeksy He is :D

[WaltherSolis]

@UnhonorableMentions english isnt my main languaje, im spanish and I alredy learn all those topics at school... so dont complain about my english..

[racionalan]

AHA ! :D

[istudywater]

This guy is not a very good teacher... smart though...

[ff7masta]

@istudywater You're a moron.

[istudywater]

@ff7masta I am not a stupid person or the city in eastern Argentina, southwest of Buenos Aires; pop. 642,000. Which definition were you wanting to use to describe me? I am not either.

[ff7masta]

@istudywater Moron.

[berniebay]

@istudywater

"Moron" and "Morón" are two different words. One had "a" in front of it implying that it was not a pronoun. Also, the city has an accent.

[WaltherSolis]

collage for this? are u kidding me...

[UnhonorableMentions]

@WaltherSolis considering you speak english like a five year old you might need to go back to kindergarten.

[alaqt]

this is high school lesson right???

[TheBobthetiger]

w w w . c l i c k t h e n c a s h . c o m

MAKE MONEY BY VISITING WEBSITES

... It's that simple.

[1683clifton]

at 7:39 prof is gonna start planking 

[keatsblake100]

@1683clifton  What do you mean??? lol Please explain

[danielagudelo001]

@Alecs4cwalk maybe you should have taken some grammar classes instead.

[vyu1294]

@Alecs4cwalk You might have studied physics in eighth grade, but your grammar and syntax is none better than that of a second grader's.

[mm20105]

race tires are wide is to increase mg

[ThomasHaberkorn]

@mm20105 c'mon

[mm20105]

@ThomasHaberkorn Am I wrong?\ if you increase the area friction will increase and hence mg will increase.

Actually Im corrosion eng. more chemis. than phys.

[ThomasHaberkorn]

@mm20105 if mg is the weight of the tire (please correct if i understood you wrong), it doesn't have much influence in increasing the max. cornering force. The side force for a wide tire is higher because the contact patch area is higher (sheer stress * area) and because a wider tire is softer:

In a low-slip regime, side force is linear to slip. Lateral stiffness of a wider tire is lower here than of a narrow tire of with same composition (derived from Hook'es law). ->fric. coeff. is higher

[mm20105]

@ThomasHaberkorn I thought that mg is grav. force.

[ajudaaduja]

@mm20105 g=9.8 N and it's almost the same everywere on earth, and it's our planet grav. force. But when you are talking about an interaction of a planet with a object them it's called weight, which is calculed m*g. Your mass is always the same everywere in the universe, but your weight varies depending on the gravitionnal force of the planet you are interacting with. It's simple.

[mm20105]

@ajudaaduja thank U

Im back to class >>:)

[ThomasHaberkorn]

@mm20105 it is. Weight is the grav. force in Newtons, Mass is in kg.

[kawsihen]

the only thing that makes me worry is that I was not educated in an English country

[Zeldakitteh]

I would argue that wider tires do matter for the angle at which the vehicle starts sliding if the road is not completely flat, which roads mostly are not.

[joeyvigil]

@Zeldakitteh yah you could argue that because it makes sense, but experimental evidence proves it is false.

[Nettikadlez]

@joeyvigil Roads consist of various materials (If it is asphalt, for instance). Some of those materials have lower friction values than other, thus, a thinner tire, which on a non-uniform road could avoid some of the materials with higher friction, would conceivably receive less friction.

Size does of course not matter if the road is of uniform material without variations, like roads usually have.

(My other account was blocked for some reason).

[annuitcoetis]

take the exemple of a bicycle wheel. If you have spent any serious time on a bike you know the thin wheel has a lesser grinding effect into the asphalt then the wider ones and so a lesser "bite". As the temperature gets hot in the afternoon the fat wheel will slow you down even more and actualy starts to feel like gum on gum. You can actualy hear the sound it makes as it "sticks" to the ground. So I thanks for the lessons in absolutes but out there under the sun, there's no such thing.

[pop1nn]

I remember in college I had a teacher trying to explain this with a bunch of stupid situations about cars and shit... After 4 minutes listening to this guy I'm like : that was that fucking simple

[Thalesf100]

In Brazil, we have those lessons, about friction and everything on the 3th grade of high school lol, and u'll learning it >>> MIT .... Dude, we learn that even before we get into university or college.. in fact, we need to know everything about biochemistry, organic chemistry, everything about physics since eletromagnetism till classical mechanics, etc.... we gotta learn also everything that u see in math just to do a big teste called VESTIBULAR. (to get into university)

[Azideofmyg0t]

@Thalesf100 So why is your country a wreck full of aids, gangs, and lazy people?

[html5labs]

@Azideofmyg0t lol, aids, gangs and lazy people?? you need to travel a little more man.

By 2016, Brazil will become the 5th stronger economy in the word.

aids is also in USA, gangs??? well, you have had bad experiences with that in detroit and LA, right? I bet you have a gun under your bed.

lazy people?? well, in the USA you find a lot of people that lives just for drinking beer and see TV

So don't judge something you don't know, or something you see only thru the hollywood movies

[quarfv]

@Thalesf100 You definitely don't sound full of shit.

[elementoxygen]

I am only 11 years old boy following the lecture , an amazing proffesor

[FienStudios]

I haven't even started Physcis since I'm in the 9th Grade, and this I understand....... A's and PhD here I come :D

[dansoftheways]

Great teacher !!

[imthetopstoner]

Respect the unbreakable Laws!

[Ghaiyst]

damn thats an awesome observation. mu of s is simply the tanampha when alpha is less than or equal to 45 degrees since mu cant be more than 1 or it will start sliding. this would have helped a whole lot!

[yalesonny]

I love the lecture

[patarthenry]

Professor Lewin enthusiasticaslly vitalizes physics so much so that never have trig functions, decomposed forces, ramps and massless strings been so fascinatingly attractive.

[Sinjinator]

His accent sounds like a guy who sells weed ;)

[julaz360]

@Sinjinator WTF...



[bosshoggett]

Ahhhhh MG cosign alpha hu.... yikes!

[jo17171717171717]

this is IB1 core physics...first month of lessons, 16 years old

[AnNaCiNdErElLaRoCkS]

(L) FRICTION (L)

[wrexhamseadogs]

7 people dont understand physics :)

[mejicano3333]

he said weight is not a factor, but then what about inertia? doesn't that apply that the heavier the object the heigher its inertia, hence more force is needed change it from its state of motion? I know he showed it mathematically but i would really appreciate it if someone could explain it to me, thanks

[dwh56595]

@mejicano3333

in the part with the static friction it doesn't matter, because nothing is moving.. And with kinetic friction, as far as I know, newtons law is in absolute coordinate system, so that means that inertial force isn't taken into account, because we don't see the unexplainable force on a body (inertia) if we are not a part of this body.. And if my claim is wrong (I'm sure someone will correct me) then we have a possibility that inertia is included in m*a, so a=a normal + a inertial..

[RockLegendLeo]

@mejicano3333 thas because in this example the object may seem dimensional but it actually represents a dot without dimensions.NOW u know that all objects regardless of mass fall with the same accelaration when they are into a gravitational field without air ressistance.thats the same reason why mass isnt a factor at friction.but that is not in reality but in ideal siuation like this one.im not quite sure tho about it.

[plastabrick]

@RockLegendLeo Consider throwing a rock from a helicopter hovering at 5000 feet - if the rocks physical dimensions remain fixed but its density is increased, it will create a larger hole in the ground on impact.

[plastabrick]

@mejicano3333 If you double the size of a large rock, you have twice as much chance as killing a member of the public if you throw it of a high rise building

[YouGotTeaBagged]

Is this really what they teach at top American universities? I learnt this shit when I was 16 in school.

[TheAspiringOne]

@YouGotTeaBagged Coming from someone named "YouGotTeaBagged" ... ... Sure you did; Whether or not you retained any significant ammount of that knowledge, is another story.

[rsotbairnfire]

Knowledge and understanding are two very different things, and it just so happens that Walter Lewin was an amazing professor in terms of promoting understanding. Don't be hating on MIT!

[purpleleach1]

@YouGotTeaBagged Yeah same here, but this is only an introductory course in physics and not every one has learned this going into college. It may be a review for some and can fill in any missing gaps in their understanding & knowledge of physics. A lot of high school courses do not incorporate in the calculus either, unless AP Physics C is taken. I would say this professor is way finer at teaching physics than my physics' teachers ever were.

[Ondro1112]

I was not getting it untill i found out that he was not saying mutants, but Newtons :D

[Iridium237]

What is he wearing on his wrist?

[scorpionboy3]

He always brings an interesting item on him, or his wardrobe, today is that bracelet.

[Rookycastle22]

hehehe, makes u dream of beyond high school to the wonders of uni!!

[aboo00oode992]

damn it , i am a midicine student why they have to give us physics course !!!

damn it .

[cormacobroin]

@aboo00oode992 Because it is damn damn easy and you should have a basic understanding of the world around you? And to think i am still at secondary school...

[aboo00oode992]

@cormacobroin i know , my marks are good BTW but i just hate physics so much !!

too bad my prof. isn't as good as this one so i'm here :)

good luck .

[junior1984able]

do you guys think that all the formulas of physics is stuck in the professors brain or does he glance at textbooks once in a while to remember them

[plastabrick]

@junior1984able The friction associated with the professors formulas are not greater than the forces generated by his memory loss.

The text material that he sometimes reverts to suppliments the friction of the formulas - thus preventing them from slipping from his mind.

As we age, the friction in our brain lessens as memory retainment begins to decline.

Strolling around inside the head of someone with amnesia would be similar to riding a pushbike on an ice skating ring.

[CRISNCHIPS12398]

@junior1984able I'm sure that he remembers most if not all the formulas. After working with them for so long, you would memorize them.

[hanxdynasty]

why cant i have this guy as my prof. my current prof sucks -____-

[MObaid27]

7 got F in physics...

[inali3]

this dude reminds me of christopher walken

[demon2645]

Hello, i am a high school student, can you ask questions during the lecture in college?

[ChicagoWhiteSoxFan]

@demon2645 no, you'll be kicked out immediately if you don't get it the first time >=(

[cookielovermia]

@demon2645 Yes, you can. But only if you think it's a question other people might have. If it's not, then you should wait til after class.

[ismelloftoothpaste]

He's much better than my teacher at drawing straight lines. He's like a pro :O

[worzelhund]

so why do have race cars have huge tires?

[WWEFAN952]

@sonalgoodgirl same 2 me xD

[angusslash12]

@sonalgoodgirl We learn this in high school also, The best way to learn advanced physics in college is to be an absolute expert of simple physics. Notice how this is just one lecture.

[galluh123]

so why have racecars wider tires???

[JasonVladimir]

@galluh123 Good question.

[NilsMcCloud]

@JasonVladimir A wider distribution of the friction force allows for more control.

[sriharipala]

I am from canada. my university is top ten university in canada but it does not have a good physics instrctor for classical physics . MIT is best

[MsAllahhuakhbar]

@sriharipa`PERHAPS YOU SHOULD LOOK INTO ISLAMIC COUNTRIES...USUALLY ISLAMIC COUNTRIES ARE FAR MORE ADVANCED IN PHYSICS COMPARED TO INFIDELS COUNTRY!`MALAYSIA IS ONE OF THEM...

[SuperSaddam123]

@sonalgoodgirl lol everyone is this is just the intro parts normally with A-levels you can skip 8.01 but i doubt any highschool teacher can teach like professor walter lewin.

[ratatulsuprem1]

great teacher. very stable educator

[griefer1]

i thought that if a body was moving in the x direction that owuld be cos not sin.

[baaroodii]

09:45 never understood why they think they slide at the same rate.

[nosekta1234]

Damn, AP physics B is much harder than this. Or maybe thats just because he's doing Newton mechanics.

[WulfPMG]

I'm in 6th grade... so... why am I watching this again?

[ironstealer87]

He is the only guy who is helping my pass physics class. God, physics turn out to be more challenging than I thought. Its no joke, but understanding a concept can create a big headache. Thanks to Prof. Lewin's lecture, I am understanding and barely the college class.

[mursie100]

6 people fell down !!!

[lucile1010]

he kind of sounds exciting when hes explaning..

thank you very much for sharing your knowledge!

[ashishrs]

this maan sounds like richard feynman.....he even looks like feynman.!!!!

[1RadicalOne]

Actually, no, he sounds a bit like him, but looks quite different.

[baaroodii]

@ashishrs YES

[CharlieTan84]

Got a question!

If the friction is just tangent(alpha) how come is that possible that it depends on the material?

I can't get it.Any help?

Thanks

[YesYou123333]

@CharlieTan84 tangent(alpha) only defines what the angle is when the material starts to slide.

[CharlieTan84]

@YesYou123333 Ohhh now I get it!

Thank you very much for your help my friend!

Have a nice day

[dsanzo]

@CharlieTan84

Because the angle itself depends on the material, as you saw in the demonstration.

[CharlieTan84]

@dsanzo Thank you very much!