Lec 5 | 8.01 Physics I: Classical Mechanics, Fall 1999

[MohammedSalim2013]

احلى ما في الموضوع ........السبورة !! :)

[LOL7877]

@vegapunkboy

Yeah I agree, I first encountered UCM in Grade 11 ( 4th yr HS here in the Philippines) haha.

[heavymetaldeath4life]

Water is so stupid...lol

[VersieJimmybl438]

so schaut mich an bin ein frosch

[jeweetut070]

this is epic

[moah2012]

edit: v=w*r right? so 63*10 = 630....

Also the dimensions don't work....

63 rad/sec * 10 cm

[moah2012]

I am confused w=63 rad/sec so v= w*r so 63 r*10 = 630? why is it 6.3?

[Machinima2013]

@moah2012 10cm = .01m

Use meters

[bfich123]

@moah2012 because the radius is ten centimeters.... the standard unit of measure for any length is in meters therefore 10 centimeters is equal to .1 meters.. try it now and you should get the right answer

[moah2012]

@bfich123 thx

[vegapunkboy]

wow...this is university level??

i did this in grade XI

elementary stuff....

[heavymetaldeath4life]

@vegapunkboy This was an introductory session. The lecturer wanted to make sure that the basics were covered, before going in complex problems.

[vegapunkboy]

@heavymetaldeath4life hmm...ur right...

[redrum41987]

flawless lecture too

[redrum41987]

awesome use of the space station

[zeroMPUA]

I am glad for MIT students that they have a very good lecturer

[miccollo060]

11:30 it just goes "schwee, schwee"

[GornallB]

I love his drawings of people on strings. :')

[YouEatSht]

he takes an hour to teach a chapter in my physics book. my teacher takes overtime keeping us after class to re-learn physics as she goes along. so much for taking an AP course with a teacher who needs to ask the class if her answers are right.. /facepalm

oh may i add she gets angry easily when it's not our fault we don't get what she is talking about.

[drag0nfig0]

I can't stand his voice...I don't know why, I just can't focus if he's talking.

[leeyihlun19940520]

the prrrrrrrrrrrrrrr dots

[eyeamon]

learning sooooo much

[MrChimei]

The students look so fucking morbid, despite having one of the best lecturers of physics since Feynman

[DevonHenderson100]

does this man still teach?!?!?!

[leeyihlun19940520]

@DevonHenderson100 yes he does

he is the Professor Emeritus of Physics at MIT

[LeadVitamin]

@leeyihlun19940520 Emeritus = Retired.

[Mercymanful]

a ball in the center and a disk around will be an ufo loooool!

[Mercymanful]

let me guess I need a black-controlled holes in my ship centered to get gravities of my ship-centered ;)

[Manolao]

what book do they use!? I need one!

[shorryukenctw]

Thanks MIT ~~

[JaySmith91]

I wonder if anyone at MIT can clean up these videos? Great teaching, low quality footage.

[shinymeowth1]

Close your eyes and listen to 24:09.

[a4b3c2d1e0f]

hahaha awesome lecture :DD

[AegisRick]

Guys I love the dotted line he does on purpose.... Someone teach me this..... I MUST KNOW

[JaySmith91]

@AegisRick He's the only guy I've found that does it. He slants the chalk towards the direction that it's moving so that it easily catches the board and jumps.

[tach0171]

hahahahahah PLUTO!

[GrowMasterGeneral]

Medicine wheel @27:18 

[MrBuffalow77]

you may have just saved my A grade

[nivu007]

at 42:00 he says if u make Ac =9.89 the rope doesnt pull and gravity provides the Ac...how is it possi... as Ac should be ALWAYS towards the center and Gravity is only towards the ground??

[mdiem]

@nivu007

Not sure what you're referencing at 42:00, but I think the situation you are describing is at the instant that the object is at the top of the swing. If the a_c is the same as gravity then the a_c at that point is only due to gravity. The force on the object and on the string is the same and there will be no tension in the string.

[brus0li]

Awesome! Now I understand how the space stations in 2001 Space Odyssey work!

[sometimesilovelife]

is this college level, or highschool ?? what level is this? and what could be the age of students attending

[BeLieVeR11111]

@sometimesilovelife this is university man. Have you ever heard for MIT??

[sometimesilovelife]

@BeLieVeR11111 i know what MIT is , i'm not American , i just want to know what level is this because i'm still in highschool (baccalaureate) and already studying the same things, for international students what level is it ? i'm guessing 12

[tach0171]

@sometimesilovelife first year in university is some time a review of high school stuff + this is the first few lecture so u would have learn it

[BeLieVeR11111]

@sometimesilovelife this is university man. Have you ever heard for MIT?? Please don't answer that...

[blinginlike3p0]

I am no physics expert, but what is the purpose of finding the centripetal acceleration? meaning an applied purpose. All i can think of is finding breaking points of a rotating mass, like the max speed for a propeller or something.

[Exiemus]

This guy's teachings are wrong, the correct solution is AC=W2R=30,000 M/S at 36:29 also Cannibalism is universal and ultimately necessary.

[ginamarienavarra]

i can't wait to say that i got an A on a physics test because of a MIT professor! haha he teaches way better than my professor!

[behnamasid]

I love how he is enthusiastic about teaching, I wish I had teachers like him.

[rotnem07825]

I feel like, from reading the comments just as I start the video, that I'm going to love this! /me grabs notebook out and participates

[zkhandwala]

At 35:00, when the effect of the centrifuge on the "light particles" is being explained, there is something I don't quite get: why wouldn't the gravitational force (due to the centrifugal action) have the same effect on the water molecules as it does on the particles, and thus keep the particles in suspension?

[avedorena1]

@zkhandwala

that's because it is not the weight of the water molecules that keeps the AgCl particles suspended but rather the intermolecular forces of water (e.g. surface tension) these forces don't depend on mass and therefore are not altered by the action of a centripetal force. Therefore, at a point where the weight of the particles is increased sufficiently to overcome the intermolecular forces of water it sinks to the side of the container where it experiences the greater force of pull

[ry7ky]

@zkhandwala the same force isworking on the water particles, but water is really good at resisting compression, thus it doesn't get dense as fast as the particles gain weight, and the particles sink. That's how I understood it anyway, hope it helped.

[elarssen91]

Physics works!

[paulinaguta]

I'm studying for my MCAT currently and I've forgotten important concepts in the past 8 months since I've had physics. The experiments have helped me visualize some things that are not as intuitive as others. These videos are a great aid. Thank you Professor, these lectures are much appreciated!

[YesYou123333]

During my undergraduate years I had a great Physics Instructor. Even better than this one. He had a Ph.D from The University Of Chicago and his instruction encouraged me to make it through college. This was at a local Community College. Just wanted to say that all the great Instructors are not just at the top schools. Thanks Dr. Lecuyer and all teachers who share their knowledge. Without them, our world would come to a standstill.

[RubikCuber1]

@YesYou123333 i do agree that not all the great instructors are at the so called "great" schools, but I think that it's a seriously subjective matter to say that one teacher is better than the other. A great teacher to one will most likely be a terrible teacher to another. Obviously, there are certain qualities that make some teachers better than others, such as enthusiasm and patience, but others are intangible and can't really be quantified like that.

[PalestinianAK47]

This professor is my dream professor when i get to college. This man explains things way better than my high school teacher.

[takekideasy]

can someone explain what he said started at 34:27 about lighter particles and heavier particles. i cant hear clearly:'(

[takekideasy]

MY PHYSICS TEACHER IS ONLY A SHIT COMPARED TO WALTER LEWIN.

[2129261184]

Gotta love him, great teacher!

[Antoniocastagnoli]

The professor is Great! I want to be like him as a physicist. How about the equation Ac=v²/r, I can deduce it, but it's not necessary any devivative, but know the way to deduce using derivative. Ask me on facebook.

[keeranx]

Pls, show derivation of Ac=V^2/R ...Please.

[eternity00000]

@keeranx consider a isos.triangle with very small theta between 2 sides so as magnitude of v does not change, the third side is (v)(d(theta)) which is delta v dv=vd(theta) dv/dt=v(d(theta)/dt) a=v w (w is omega) by same theory replacing the velocities by radius with the third side(arc) s since theta is very small , consideer it as a straight line so s=rd(theta) ds/dt=r (d(theta)/dt) v=r w so we get a=v w v=rw acceleration =v(v/r) =v^2/r or r = w^2

[behnamasid]

He is so enthusiastic about teaching, he even brought lettuce and spinach to demonstrate centripetal acceleration, the best ever.

[LFZ15]

Walter Lewin is a bamf.

[Ambidexter1979]

Great!

Sounds like the prof. is Dutch.

[carlaberkowitz]

i want to be in your class

i love the accent, drawings, and reference to grandma

[MrKBentley]

In large schools such as MIT there are two parts to each class: A lecture (what we are seeing now), followed by smaller group meetings lead by graduate students. That is where the examples are worked, questions answered, ect...

[lompocus]

@MrKBentley

And this youtube comment system seems to be many's pretty horrible substitute for the second segment of those classes xD.

[jiggaluv123]

@MrKBentley I think that's a standard in any legit university.

[mufc4everch]

@MrKBentley I think its like that at most universities

[aferreira917]

Good for you! Welcome to physics level one.

[gr0mithtimon]

Gravity is not instantaneous, stupid dumbass. Gravitational waves travel at the same speed as light in a vacuum.

[Skeptic121]

@gr0mithtimon Newton noted that if the earth accelerated in the direction of the sun eight minutes ago, there would be a component of acceleration in the direction of the earth's orbit, thus, the earth's orbital speed would increase.

This paradox was resolved by General Relativity: gravity propagates at the speed of light but the earth nevertheless accelerates toward the actual sun, not in the direction the sun was eight minutes ago. Hardly obvious!

[minyquai]

@jron12104 so gravity is faster than light? o i c.

[bigscottius]

gravity has a greater acceleration than light:P

[a3d3i3l3]

that's cool,but i expected more problems to be solve,anyway cool

[LAAA2]

This professor is great! The way he explains things is so accessible. Thanks, MIT, for posting this to augment my course at another institution.

[RomZomCom]

Agreed. At least it isn't some technobabble, as was the case with a few classes here. -_-

[Pudersepp]

The amount of knowledge you obtain at a University grows exponentially. So does the amount of information in this course. Starting out nice, then you go whoosh-- And the fact that you "have done this topic many times", does not really give us any useful information. They are in the high school of that country as well as they are in yours.

[Darksideofthecole]

It depends on the classes you take in High school. I don't attend MIT, but I'm assuming that he is covering the basics as a refresher so that he can continue on to the more complex physics.

[rishigenius1003]

seriously im doing this at school!!

[femtophysiker]

same in pakistani schools too....

[killintymm]

and they will take it again in college to start off with more elaborate topics. because everything is based on the basic concepts. if you learnt it in one class you dont review in the next ? please think

[Marikino]

That chick doing the swinging demo at the end of the video is pretty cute.

[selahia]

he is a geniuos teacher.

[headbanger623]

@selahia lmao, learn how to spell genius.

[MitchellJKnight]

@selahia You have genius spelling

[ehswan]

Seems to imply that the speed of gravity is infinite.

[AD2948]

I believe you mean force not speed-and no its not infinite,just in Newtonian physics

[CanisLupus1987]

Gravity is dependent on the mass of the object.

You also exerce gravity over things, though earth's attraction is so much stronger that we barely notice attraction between other objects.

but at an atomic level it's possible to study that.

[Sumdude0]

Energy is a scalar, not a vector, so it has no direction.

But the object does have a velocity, always perpendicular to the direction of gravity, not in the direction of gravity.

It's exactly the same as the ball swinging on a string. If the string is cut, it flies away on a path tangential to the circle.

When the floor is removed, not only is the force of the floor towards the center removed, but so is the perceived force of gravity.

[UninstallingWindows]

could somebody explain me the part starting from 30:00 with the space station.

isnt it kind of contradicting fact that the object that would fall out of the space station would move perpendicularly to the gravity perceived?

its as if i juped off a cliff and not fall in the direction of gravity but fly away like a batman=S

[Sumdude0]

When an object falls out, there is no more centripetal force (or push) of the floor on the object, and its motion is uniform.

When you jump off a cliff, there is no more force of the cliff on you, but there is still the pull of gravity, which causes an acceleration.

In the space station, gravity is perceived from the acceleration, but is not actually gravity (the force of attraction between two bodies of mass).

[UninstallingWindows]

"In the space station, gravity is perceived from the acceleration, but is not actually gravity"....but it is still a linear Force, a huge force, that suddenly changes its direction 90 degrees. as newtons law says: "A body at rest stays at rest, and a body in motion stays in motion, unless it is acted on by an external force."

the object in the space station has huge Kinetic energy in the direction of perceived gravity. it wont move int the direction of gravity cos its acted on by the floor.

[UninstallingWindows]

comment pt2

now, remove the floor, no force is acting on the object anymore. so the huge kinetic force should fly away in the direction of perceived gravity, unless some external force acts on it, and changes its direction.

[opiumgland]

On the station's rim, an observer is accelerating towards the axis of rotation, but his velocity at any moment is perpendicular to the acceleration. The illusion of gravity is caused by the friction between him and the bulkhead. If the portion of the bulkhead in contact with him suddenly dislodges, he is no longer acted on by the station's CA. He flies through space at constant velocity in the direction and magnitude of his velocity at the time of dislodgement (see conservation of momentum).

[jinaiiiii]

How is this video 50 minutes long?? I thought the maximum was 10...or is it because of the special contract?

[BrianDiehr]

special contract.

Since it's for educational purposes.

[soom66]

this guy deserves to get a Noble prize for excellence in teaching Physics.GREAT WORK!!!, makes u realize the real essence of concepts.

[thevidfather]

I agree. These lectures help me so much with my high school physics classes. He has already received a number of awards for his teaching.

[QuintenFGC]

Great, great teacher. I am student of physics myself. Unfortunately I have never had the pleasure to learn from a guy like that.

[fam600]

Yeah... a teacher in a school that doesn't charge so much money.

[djbanizza]

I wish I had such a physics teacher ...

[iluvjiyongx3]

oh dang! this stuff is really cool! a bit of difficulty with the terms, but overall i learned a lot! love how this teacher always demonstrates~

[Renukanimmi]

wat is the difference between centripetal accelaration and angular aceleration?

[eoinbrett]

Ok, angular acceleration is the measurement of the acceleration of a body moving in a circle in relation to the angle "traced" out in the center of this circle.

More precisely it is the second derivative of the change in the angle with respect(d²θ/dt²). It is just an angular version of our normal interpretation of acceleration, the difference being that with the acceleration of a car for example we look at the rate of change of position as opposed to the angle.

[eoinbrett]

For centripetal acceleration. Now if you consider that a body needs a force (acting towards the center of the circle) to keep it moving in a circle of constant radius. And for every force there must be a component of acceleration (f=ma), this being the centripetal acceleration

[ymcho92]

what is centrifugal acceleration??????

[ShaunRL]

when something moves in a circle its essentially moving in a straight line but being constantly pushed in, the force pushing it in is the centripetal force,forces always act in pairs like when gravity pulls you down the ground pushes you up so your legs get tired or if you push against a wall on iceskates the wall pushes you back and you accelerate back, the paired force for centripetal force is centrifugal forced and its equal to it and acts in an opposite direction,

[ShaunRL]

putting a force on a object creates an acceleration in the direction of the force, the magnitude of acceleration depends on the mass of the object and the size of the force, a=f/m

so this centrifugal force creates an acceleraion opposite to the centripetal one and its proportional to the mass of the object

[hamiltonbulldogs]

Great lecture

[Alfonso1031]

i want to ask

whats the difference bet.

angular frequency and

angular velocity

not in formula

(i'm not a english native, if i typing wrong, pls tell me)

^^

[CaptainZeep]

Well, your question is two months old, so you probably have already figured this out, but angular frequency is a function of angular velocity:

Angular velocity refers to the change in the angle of rotation over a change in time (radians/seconds).

Angular frequency is the inverse of the period (time that it takes for the object to complete one rotation), that is, 1 divided by the period.

[kp7894]

thx for ur reply. ^^,

ur explanation is wat i needed.

[BGasperov]

Speed is a scalar (its defined with its value), velocity is a vector (its defined with its lenght/value, direction and orientation).

[FALKEN2012]

This video is really helpful.

I had a problem in understnding the concept of cicular motion.

Now, I get it.

[eatadick1]

Wonderful, thank you for the upload. USF's physics professors are useless.

[3lessyaya]

Is this physics?

[FlorianWoerz]

Yes!

[jcmsp360]

the velocity is the speed with an allocated direction, i think its used because it helps the algebra, as the velocity can have a negative value also, whereas speed is linear and can never have a negative value, for example when you drive in your car along a striaght road and take a U-bend you have the freedom to drive with a greater speed on the return leg, but your velocity would be a minus value as you are returning to your origin. hope this helps and im 13 yrs old and I no this stuff

[hamiltonbulldogs]

it's also great that on your profile, you're 28. good job.

[hamiltonbulldogs]

It's also great that on your profile, you're 28. Good job.

[sorahx]

thank you so much. i appreciate this!

[munmanito]

Hi I'm not a englisch native speaker, but I understand the lecture. Can someone tell me please the difference between the speed and the velocity? Not only the formula, but the "literal" meaning. Thanks

[SPRMSSVBLCKFOTSEN]

the velocity is the speed with an allocated direction, i think its used because it helps the algebra, as the velocity can have a negative value also, whereas speed is linear and can never have a negative value, for example when you drive in your car along a striaght road and take a U-bend you have the freedom to drive with a greater speed on the return leg, but your velocity would be a minus value as you are returning to your origin. hope this helps

[darthspeaks]

Speed is length per time. Velocity is length per time in a DIRECTION.

[munmanito]

Hi I'm not a englisch native speaker, but I understand the lecture. Can someone tell me please the difference between the speed and the velocity? Not only the formula, but the "literal" meaning. Thanks

[fateaglio]

i did this at school, not at uni :S

[smell1it1gently]

this is more interesting than how my lecturer taught..tanks for sharing this..

[smell1it1gently]

where is this lecture held? which school?

[suapntdoen]

M.I.T., Cambridge, MA

[ekid2k]

it would be great to have equations in description for easy viewing