Lec 11 | 8.01 Physics I: Classical Mechanics, Fall 1999

[behnamasid]

mgh = Massachusetts General Hospital

[cutiemelly929]

-FIRST LESSON-

Students Mind: "What the f**k did I get myself into."

[redkb]

For those trying to find it. The wrecking ball starts around 46:10

[NipplesTheSquirrel]

Honors Physics Final tomorrow omgomgomgomg

[Generalvaldez]

how does me make the dotted lines with his chalk?

[WalterDianaro91]

na wohne in leipzig

[HikariOfTheAzureSky]

I love how good this professor teaches. But i also love my intro physics prof, they are both adorable grandpa like! ofc i got an A in the class and I studied 5 min before each test and that's part of why this video is so fun for me, for it reminds me of fond memories of sleeping through class, never flipping textbook open except to reverse engineer answers for odd #problems that are graded, and walking the hell out of lecture to go play mmorpgs after signing attendance sheet! xD

[morningstomper123]

I'm a carpenter. This was hectic.

[sansnomouage]

Fantastic.

[tobiasmar2]

He is so energetic when lecturing about energy.

[Pr3fixProducts]

Love this guy, I'm 15 and even I can understand it.. he makes complex things real easy.. thanks =)

[Pr3fixProducts]

@morningstomper123 I don't go to the uni, but I'm interested classical mechanics, quantum mechanics and nuclear physics. :D

[Askate]

if this was my teacher i would pass my ap physics exam no problem

[RPShredow]

whats with physicists and sandals, my physics professor wears sandals everyday too like lewin.

[shouti93]

PHYSICS WORKS !

[MrYomantanepali]

if there was no friction and air drag then if it is dropped from 2R then it should get to the top right ? thanks

[majormuss]

i see and understand why MIT is the best!

[tshenvideos]

@majormuss

Its definitely is.  I really hope that I can get in because I want to learn from professors like him!

[jxcxtxl]

WOW i would love to go to MIT to be in his class!.... rather than my lame professor -___-

[HonestMagnet]

This guy's DEFINITELY dutch!!

[1KevinsFamousChili1]

@HonestMagnet you would be correct

[IronMicey911]

I always wanted to go to MIT but never really had the credentials to be accepted. It's nice to know that MIT offers other alternative ways to still get a good quality education. It's also refreshing to see a professor that actually writes on a board opposed to clicking through a powerpoint slide. I'm not saying power points slides are bad, but important concepts can be overlooked because they go by so fast.

[GREYBLAZE800]

All i did was type in "how does a G-11 work?" and this is what popped up. Good Physics though :)

[mike060187]

"physics works and I'm still alive." See you next week hahaha



[SMGrawks]

The Black students are lucky, they don't even have to understand it to pass :(

[RJonStreetz]

@SMGrawks Who said that? really?? O_O

[thecoast47]

@SMGrawks what are you implying?

[SMGrawks]

@thecoast47 I'm implying Affirmative Action

[momo121212]

@SMGrawks I don't understand how race has anything to do with them passing. Care to elaborate?

[killser312]

what a nerd.

[RJonStreetz]

@killser312 Stop trolling dude grow up......

[killser312]

@RJonStreetz hey i have a right to complain i sit in a class room all day long, and the next thing i do is go on youtube to watch a video that is nealy a HOUR LONG

[vvsimonvv]

@killser312 If you're only here to insult him, why're you watching it then? No-one is forcing you to do so.

[tshenvideos]

@killser312

I agree with the other guy. Why did you watch a lecture when you hate sitting in lectures in the first place? Now that's definitely not logical. MIT is a place of creative logic, if you can't take it fine, but remember that they are largely responsible for creating things that you take for granted now.

[bahhv2]

screw going to physics lectures im staying home and listening to this guy!!

[Osman9100]

Svaka cast profesore. Ti ucis studente da shvate.

[hanxdynasty]

this prof makes my prof look like shit

[bahrom7893]

Best physics lecture I've ever attended!

[Zee96969696]

i dont understand how can people not like maths and physics, i mean I didn't like it when I was a kid couse I was more interested in having friends, but now i think its very interesting but it seems not alot of people like it

[Zee96969696]

im up to the chapter of conservation of energy in physics, and I don't understand anything, I'm in big trouble, hopefully these videos will help

[alleksandrs]

It is difficult to understand, how the centripetal acceleration "a" and gravitational acceleration "g" (or respective forces - centripetal and gravitational) can balance each other out, if at pont "D" they both are acting in the same direction (down). In this lecture it is at 27:55....28.00.

[jarekblu]

@alleksandrs Centripetal acceleration is a constraint (condition) for an object to remain in circular motion. Therefore, centripetal force is not a physical force, like gravity, and other forces must provide it. In this case, at point D, there are two physical forces acting on the object: gravity and normal force. In the limiting case, when velocity is small enough, normal force is zero. The only force acting is gravity and acceleration due to gravity has to provide centripetal acceleration.

[plasmaluz]

I do not need any other proof that this guy is a great teacher than 13:31. How awesomely contrasted is the old blackboard and how clear are the text/graphics. We have gone backwards with the whiteboard.

[avedorena1]

Lewin rules!!!

[shiirodance]

people here are

30% intrested in physics

70% trying whateva ways to pass their physics test tomorrow

[ginamarienavarra]

@shiirodance for me it's both. i LOVE physics but my class sucks and i'm barely passing!

[makaveli571]

@shiirodance

so close lol its one wednesday

[YouEatSht]

@shiirodance haha! i got a test for newtons universal gravitational law and centripetal forces :/

[varungargg8]

@shiirodance

donot say that walter lewin is good professor

[boxerek123]

@shiirodance hahahah couldnt be more true.

[mufc4everch]

@shiirodance lol well people who take physics course in uni are usually interested in physics so it would be higher

[HikariOfTheAzureSky]

@mufc4everch physics majors sure, engineers who are engineers because they think of building the robots they dream of but never think about the actual building process, no. =)

[zon723]

@shiirodance I have a test today -__-

trying to understand something

[Pegloj]

If I'm bringing something up, the force is in same direction as increasing value of x (if x increases from ground to certain height above the ground), therefore I'm doing positive work. Can someone explain me why is work which gravity does positive when I bring something down? Is that so because direction of increasing x flipped over, therefore it's in same direction as gravity force? (sorry for my bad english)

[DaBhaalspawn]

@Pegloj

I believe it depends on your frame of reference. For example, say you chose "i" as your horizontal axis, and pointed it to the right. Well, say you chose "j" as your vertical axis, and then pointed it downwards. If so, the gravitational force (which is always downwards) would be positive in that case.

[praxxom]

wow. he is so fast this class must be advanced than other physics class.

[dgaagjezeken]

physics works and rocks

[mursie100]

1 guy got an F in his Physics class :)

[rickyscream101]

why would you post this?? Dude...

[thangbanhbao]

GRAVITY SUCKS!

[someonep93]

@thangbanhbao Yep! But sadly, it's the law... ;)

[mariomaruf]

@thangbanhbao As in the verb sucks, not the slang.

[JMEBF]

My respects professor, I so wish I would had studied physics,.. maybe in next life,.. A to B through the unknown.

Thanks, and congratulations!!!

[kuzuboshii]

@JMEBF Why wish, it's never too late to learn.

[johnnyfun26487]

Thank you MIT professors, Thank you MIT so much. I really appreciate it.

[TheStudonfire]

teaching..physics by putting his life on the line.....

BEST THING ON PLANET EARTH....!

WISH I HAD SOMEONE LIKE HIM TEACHING ME

[simonvlevin]

LEWIN ROCKS!!!

[thelifeofbrian1]

at 25:56 is it suppose to say Ua+KEa=Ub+KEb=Uc+KEc=Ud+KEd ?

[vaidyt]

@thelifeofbrian1 yes that was a typo I guess

[AviationVision]

@thelifeofbrian1 Yep, you're right.

The = turned into a + due to pure Walter Lewin awesomeness !

[prunodagen]

@thelifeofbrian1 Yes, it's ;-)

[sumofty]

God i love this guy.

I meet 2 times a week for 3 and a half hours at my college and it turns out i learn more in a 1 hour youtube video than 7 hours of lecture time

[afghanplayr20]

i've seen 11 lectures and not 1 student has asked a question . ... are they allowed to ask questions in MIT ?

[oddieamd]

@afghanplayr20 he explains it so well, he students don't need to ask questions:)

[davsone]

he is cool one! :)

[soclives182]

cool i like it

[Rajesh26sharma]

awesome..!!

[mridularul1]

Please help me out i need help. When Professor takes the two equations and merges them then why does it come out 2g(h-2R)>=gR. Where does the 2R come from when it should be y.

[kaanees]

@mridularul1 because y is a general case ,it means for any poïnt,when he applies that to point D ,y is equal 2R

[hkpopfan4lif3]

at around 15:00 he says there's only Fy, but no Fx nor Fz....why's that? I know there's a change in h from A to B....but Fy depends on x and z....doesn't it?

Am I misunderstanding something? Can someone please help me clarify? :)

[ElizabethAGreene]

@hkpopfan4lif3 He is calculating the change in potential energy between A and B. This is the same as the change in height between A and B. Since Y is the only axis with gravity, changes in X or Z don't affect the potential energy at all. Does that help?

[SWH1990]

I have a question. What's the difference between "cross Product" and " dot product'?

[hkpopfan4lif3]

@SWH1990

dot product is a scalar, meaning, a number

cross product is a vector, and the product is orthogonal/perpendicular to your two vectors

[sodijgosdjgosdjgojsg]

Wish my teacher was like this.

[VanillaShoelace]

I wish my physics professor was this good of a lecturer! He basically reads from a power point for 30 min then tells us to read the book...

[drafhk]

Macro is correct.

x = position

velocity (v)= derivative of position (dx/dt)

acceleration (a)= derivative of velocity (dv/dt)

[definitionofis]

I got stuck where he changes from integral of distance to integral of velocities. I checked the comments. Nobody talked about that. I suspect my calculus needs a tune-up. I'm 55.

[macro312]

55....dude thats old...

[GangstaThug46]

velocity is the time rate of position

[confused1210]

v=dx/dt where x is the distance

cross mutiply dx=vdt

[GFHandelfan]

oh, i see. thanks

[MrKBentley]

Not to nitpick you Confused, but I believe it is more correct to say that x is the position instead of the distance.

[GFHandelfan]

why does dx=vdt?

[macro312]

v= dx/dt (Calculus, integration of Velocity) i think.

[Overdoz9000]

derive w.r.t time

[akujy2004]

What an amazing way to teach!

[summermoonful]

Dear Recycling....,

Velocity has lost its direction with the square: it is only a magnitude, a speed. Because a dot product of two vectors is a scalar. And the square is a dot product...

So a vector squared is always a scalar.

[recyclingismylife]

thx....not sure why it has lost the direction, but at least that gives me a rule of thumb...does it apply to other vectors too; i.e., when one squares a vector it becomes a scalar?

[CoolGurjot]

He's a dynamic teacher..........

[recyclingismylife]

He said at 13:20 or so that v squared is the speed, yet in an earlier lecture he said that velocity is a vector and speed is a scalar, so how can a vector squared be a scalar? also, aren't velocity and speed essentially the same with velocity simply having a direction?

[dastechnoviking]

if you square the norm of a vector then you get the sum of squares of its orthogonal components. And by Pythagoras theorem, the norm refers to the distance, which, in this case, is the scalar component speed.

[N1maNayrizi]

There's more to it, I see what you're saying though. Velocity and speed APPEAR to be the same thing, HOWEVER, they are not. Speed applies to total distance traveled. Velocity refers to displacement, big difference

[Wepper1]

Also Velocity is represented with a vector and speed is just a scalar

Another big Difference ;)

[TheElMarsh]

@N1maNayrizi For example, suppose this: given a length of time, we have a particle that moves from rest from points A to B. From point A, it moves at 5 m/s all the way to point B; at point B, it is moving at 7 m/s. In this example, we don't know where the particle will be moving next, nor do we know how points A and B are positioned - is B behind A? is A above B? We need direction to determine where a point is moving. The velocity "says" a lot more than the speed

[tshenvideos]

@N1maNayrizi

actually velocity is essentially speed with direction. Speed is defined as displacement over time.  Velocity has direction, so its signs actually mean something. An object that goes 3 m/s west has a speed of 3 m/s but a velocity of -3 m/s or 3 m/s [W].

[tshenvideos]

@tshenvideos If the East is defined as the positive direction.

[mathinvestor]

This is one of my favorite lectures. I like how he covers angular momentum too. If I don't understand something I go here or the feynman lectures.

[YoeriYoeri]

wow. I knew .5mv^2, but I never know that its derived from integrals. Now that I look at it, it makes so much sense lol.

[tauwarlord]

lol... i'm 16 years old and already seeing most of this on school...

[bighorn2004]

i love this guy.  he is passionate about physics and so his students are too.

[tomhuu]

love how the professori s wearing sandals with socks!

[paopao92]

that was such a clear explanation! and a memorable ending :D

[dave3030]

"Physics works and I'm still alive!"

[260191894]

@dave3030 That's my new moto now!

[rootberg]

Great! :) Unforgettable.

[09205479428]

wOOOPEEEeee... I like it. Specialy the closing punch lines.

[lilsorms202]

Last minute of this lecture, is quite possibly the best minute of a physics lecture I've had this year. My physics professor just rambles quietly to himself for 2 hrs *sigh.

[rankine182]

yeah that's right. The amount of total energy (potential + kinetic) must be the same for each point of the rollercoaster (conservation of mechanical energy)

[blitxo]

At 25:54, I think he accidentally wrote a + instead of an = (between C and D). Oh well great lecture still!

[GenDaryl]

Yhea, noticed that too.

[ryanfromjapan]

impossível copiar as matéria

[WarzSchoolchild]

Convert a 'Thermos Flask' into a heavy pendulum weight. incorporate 'friction paddles/whatever into the flask. Repeat James Prescott Joule's 1845 Heat Aparatus Experiment.

See what heat is generated with high and low values of the swing angle 'alpha'. remember at 90 degrees the 'ball/weight' is momentarilly weigtless, so the spring/paddle will be the only force acting at those instants.

Do multiple experiments. peer review the results critically! Scientific Integrity is non-negotiable!

[WarzSchoolchild]

P.S. Professor Walter is a brave man. He trusts his life to the consevation of energy principle.

Fit a Spring/Friction Calorimeter into the Ball Pendulum. The heat produced in the insulated calorimeter, just like James Prescott Joule's Heat Apparatus of 1845 Discover if?

"838 ft·lbf of work to raise the temperature of a pound of water by one degree Fahrenheit?"

Science can also be play! Predict then Discover! how change in design affects outcome of experiment. HAVE FUN! ENJOY SCIENCE!

[Anav07]

Brilliant..just plane brilliant. It is a tragedy that you no longer see prof. like this!

[catalecticant]

Brilliant demonstration at the very end of the lecture: boy, he *does* believe in conservation of energy!