Module 02_01 | MIT 8.01SC Physics I: Classical Mechanics, Fall 2010

[eyeamon]

which lecture does this go with? I imagine it is the one with Robert the monkey?

[OdellYingbr519]

na mein hintern ist geil

[muhammadzahmad]

most people are not interested in physics at all...though physics got a lot of help in our daily lives...

[agapitoflores001]

Very organized way of titling the videos.

[violetmoonster]

thanks for posting this one.

[thebigfootme]

great video

[Dating99]

Lewin is awesome!

[divorce44]

they had this on mythbusters

[devihen]

I love Professor Lewin

[theeyecreature]

I thought I was the only person weird enough to actually ponder this question

[IFE10M]

So if they go more than the speed of light the rain would be falling up... they'd be travelling back in time... awesome

[EmoPikachu23]

I love Walter Lewin =)

[Sparky5999]

He is in the highly rarefied air in teaching skills at Richard P. Feynman..

[lubos3s]

there is an easier explanation... lets bring the rain to an extreme and not the velocities of objects... let the rain be a sunlight (rain of photons) in Qld, Aus in summer... it is obvious that walking will cause more sunburn than running :)

[lemon48794879]

@lubos3s and obvious that hypothetically you can run at the speed of light at a 45 degree angle would have even less sunburn

[kurt05051987]

while discussing the least amount of rain that will pour on them 16:18, their feet will make different cosine and sine angles with respect to the velocity they would run.

[shadowC10ne]

Very interesting! I don't care what others say.

[cake89]

lol his enthusiasm is infectious, i couldn't help but chuckle watching him.

[pablo19852000]

I just saw a myth buster episode, and based on experimental data, when walking they catch the least amount of fluids in their cloths.

[matsubokkuri]

if 30 degrees, 3.5km/h.

[quablepy]

"Physics", real natural science.

[a3nebigby]

Is he dutch?? :)

[juha3juha3]

@a3nebigby yes

[Sshocker17]

he is so fun to watch. great teacher.

[onlyinter88]

He could've made it easier and concluded that the rain you sweep in your way is always constant and has nothing to do with your speed

[FabianyJoann]

Walter Lewin <2

[prettysaphire]

I LOVE HIS HANDWRITING.

[Veto2090]

TLDW: Run in the rain

[gaynorvader]

Also, people always forget to factor in puddles in these sorts of experiments, splashes caused by running can drastically increase your wetness.

[gaynorvader]

Wow, magic rain! It's falling so slowly, must be in slow-mo ;P



[oldskoolchopperboy]

Physics = 0

Math = 1

Entertainment = 1

Educational = 0

Charm = 1

Overall score:

60%

[TheAutoSleep]

The sound of the pen on the paper gives me chills. :S

[pattcom]

Hmmm, why use Expo dry erase markers on paper?

[SiberianEskimo]

baller.

[pratman2]

Is is just me or does this guy have to be kin to Christopher Walken.

[tsami7]

@pratman2 I was thinking the same thing :)

[techin5official]

WHy is this guy so excited?

[Calgarylames]

@techin5official If you were a math geek you would be too.

[rsotbairnfire]

@techin5official The real question is: why don't more people get excited about these things? Physics is amazingly cool, and I would love to have Walter Lewin as my professor!

[MrMaxen92]

@rsotbairnfire

Same here!

And the AMAZING thing is that i've had this lecture in another langauge (since i'm Swedish), and I could understand every equation, variabel, absolute term etc. crisp clear. I did have a good teacher in physics when I learned this and among other things... But having Walter Lewin as an teacher would be best thing ever :D

[Conscars]

The answer: women are always right.

[ninjaodeath30]

TL;DW Version: walk at an approx. angle of 45 degrees or the same degree as the rain and as fast as the rain is coming down.

[AchtungPakhtoon]

the Professor has an uncanny resemblance to Christopher Walken....even sounds like him at certain points.

[NavalJanistor]

Wooooowowwww .... So Idealistic!! Just run as fast as rain fall and then make yourself's angle 45 degree 55555+

[parceritaz]

Women are always right...proven by physics lol

[HighWarlordJC]

Every time I see a great teacher I tell myself they are the best. Every time I find someone better. This guy is awesome.

[aspiziri]

17:46 for the answer

[babaozhou123]

need the tl;dw version of this.

[bcbird]

Can someone summarize the video in one sentence?

[YTBIU]

@bcbird Run Forest Run

[fedetrabu]

@bcbird one word: RUN!

[Calgarylames]

@bcbird Women are always right

[MrWhatdoyoucare]

@bcbird run for your life ....lol



[aliabobalia]

women are always right :)

[gerlosgm]

Funny! :-)

[Liface]

He's Dutch! That explains the accent

[brentyager]

Is that Larry King? ;)

[schenonef]

but OF COURSE we noticed a square was missing! hands up (or rather: thumbs up) those who did!

[schenonef]

but OF COURSE we noticed a square was missing! hands up (or better, thumbs up) those who didnt!

[Holyhellitsgregory]

educational and practical; very nice

[suska12]

what if there was a wind and its facing them as same as there speed thats mean that the rain will hit there heads - he forget to consider the wind's speed and it's angle / im not judge him or anything i just though what if there was a wind or a storm which will change the wind's angle every seconds for instant

but overall i wish i had a teacher like him i would love physics

[SarahsAwesomeAccount]

That old guy looks/sounds like he could be Christopher Walken's cousin.

[6059854623158]

Buy an umbrella?

[loansharkify]

mistake!

he misses out a squared sign on Vrain at 13:40

[adman123]

@loansharkify ... and then he corrects it at around 15:30.

[vidarpi]

@loansharkify clearly u stopped watching because he corrects himself later

[mgibso29]

Best moment at 15:26. Amazing...

[Davgil1994]

Nice ring.

[evanescentdevil]

In The High Speed Like the Speed Of Light, The Object Increase It's Mass, Then the Amount Of Rain Will Be Bigger Than That.

also the relative speed will be great, and then speed of the rain drop that will hit their body, will be like a bullet and kill them,

also because of that high speed, they push more air and that mean the air preasure behind them will be 0, and that will make the the degree of the rains change it's position and hit them in the end

[steefs82]

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traveling at a speed equivalent to the speed of the rain falling while tilting forward causes this type of void with your body, the top of your head essentially becomes the "broom" sweeping up the rain. the rain under your head will fall before your front can catch it, and the rain behind you will not fall fast enough to land on your back. this what @caramonspace is explaining.

[steefs82]

@steefs82 ugh, that did not turn out the way it looked in the comment box. hopefully my written description helps to make sense of this mess, lol.

[siasabora]

I want to go to his class....

[tidewv]

The amount of water in front is always the same! Frontal area x Distance x rain density. Your speed does NOT change the volume of rain you have to sweep out of your way. Rain not swept up falls to ground replaced by new rain coming down. The only change is how fast you are travelling. Faster means less rain hitting your head and shorter time to get hit. Slower means more rain hitting your head and more time to get wet.

I think Prof Lewin got to carried away with his vectors.

RUN!

[caramonspace]

@tidewv Close, but no cigar. If you are running at the speed the rain comes down at a 45 degree angle (and are in a cardboard refrigerator box for experiment's purposes), you will see minimal rain hit both the front and back of your body, and are thus 'sweeping up' none of the frontal rain you mentioned, since your frontal velocity, being the same as the downward velocity of the rain, is causing the rain you encounter to just glide past the front and back face. Just the head gets wet.

[caramonspace]

@tidewv (cont'd) The rate at which it apparently glides past your front and back as you run forward is equal to the square root term of the vector magnitude mentioned in the video.

[freethoughtmusic]

I think I'm going to hang out here more. Hopefully this is too erudite for the usual trolls that slime every comments section. Great site!

[TheEventuaLDJMIKE]

what about the shoulders??

[Zeykieee]

:D!

[TheRealBlackRefleX]

05:24 This would resolve in devision by zero => error :D

[boomludacris]

@TheRealBlackRefleX no you stupid, do the fuckin limit ,something divided by 0 equals infinite dumass, go to school and take your calculus 1 class

[TheRealBlackRefleX]

@boomludacris why so agressive? what do you mean by limit? in school we learned that division by zero is not acceptable. so you tell me its ok to divide by zero because its infinite? maybe schools in germany teach other math rules as in usa?? :D

[hawkinsst7]

@boomludacris - i can't believe I'm correcting math on youtube!

x / 0 is undefined, so @TheRealBlackRefleX is technically right.

In fact, the whole reason we need to use a limit there, is because the problem can't be answered using the real numbers.

You're probably thinking of the fact that the limit of x/n as n goes to 0, approaches infinity

the two are not the same, though they're related.

[hawkinsst7]

@boomludacris - i can't believe I'm correcting math on youtube!

x / 0 is undefined, so @TheRealBlackRefleX is technically right.

In fact, the whole reason we need to use a limit there, is because the problem can't be answered using the real numbers.

You're probably thinking of the fact that the limit of x/n as n goes to 0, approaches infinity

the two are not the same, though they're related.

[renzyq19]

@hawkinsst7 I sense you're missing the point.

[palaver87]

only physicists can look baller with that hair

[Deicidead]

What if rains stops?

Where's your science now!

[sammyByou]

In case anyone is actually trying to calculate the mass of rain falling on P&M's head for a certain scenario using the eq shown at 14:20. Note there is a mistake. The Vrain in the square root term should also be squared since this represents the magnitude of the rain, or speed.

[dodoboy1212]

@sammyByou he corrects it later..

[MultiBrados]

A little bit long for such a simple problem, nevertheless it is great so most people can understand.

[angel13061987]

I have a question:

Shouldn't one use the derivative of the whole (water on top and front) equation relative to Vpm to find for which vpm the wet-ness becames minimum?

[Pensador]

Two words: Christopher Walken.

[novicatalasic]

This is the best video on youtube.

[shnako]

Lol, my math says the result at 06:40 is 1/3 * 10^(-4) rather than 3 * 10^(-5).

[PK34646009]

At 13:21( if I am not mistaken ) he didn't see than he should write below the square root Vpm ^ 2 + Vrain ^ 2 . But overall it is a great video and i would like more of this !

Keep up the good work and if I'm wrong write a comment telling that and explaining why I'm wrong .

[Slider68]

I know this is off topic, but I've been reviewing Professor Lewin's presentations to try to find one that covers Earnshaw's Theormen but so far I haven't found one. Can any of you point me to the right one (assuming there is one). I also wondered if he has covered what I consider the "classic bicycle problem" where you push rearwards on a pedal that is at the bottom of stroke (standing off the bike) and ask which way the bike goes?

[player1vladimir]

So next time when it rains instead of an umbrella i should calculate the speed of the raindrops and get a hat :) and run.... without stopping....

[arunk279]

if the assumptions are 0m/s and a larger speed.to answer the question of who gets more wet is obvious.The person who stands without moving(0m/s) gets more wet as the rain keeps poring as opposed to the latter case where the rain pouring will end eventually. They are also not taking into consideration actual humans, whose area calculations are more tricky; Peter is wrong in saying that rain will hit only head when they walk slowly as the shoulders will also get wet and the raindrops trickle down.

[scorpionboy3]

Cool ring, what is it?

[Slider68]

Watching a few of Professors Lewin's lectures brings back memories from when I was in University (~25 years ago). I don't recall any of my professors having such an eager and interesting teaching method though. Do all of the prof's at MIT perform lectures that are as interesting to watch as Professor Lewin's are?

[z50king29]

THIS GUY!!!! SO AMAZING!

But have fun running at a constant speed with a 45 degree forward angle.... hehe

I love teaching

[TheeDelibird13]

You know you can also just learn something from just going outside in the rain, and seeing for yourself what happens when you do whatever in the rain.

[mywtfmp3]

this is awesome, but he can do more to prove his conclusion.

[andresdambrosio]

That guy is a genius! I love you man!

[junior1984able]

why would the direction (angle) of th rain matter?

[AA10Megaviv]

In my opinion the conclusions he assembled are pretty inspirational and interesting but also too theoretical and too loaded with assumptions. However, he reached them with a vivid spirit which I found splendid and charming. :)

[anilsenturk]

had a similar prof that got his BS from MIT, was an amazing class

[somethingesoteric]

What a fantastic teacher.

[ctiebs]

@ 13:55 wouldn't it be the Vrain^2 as well? Also @blomman , do you think understanding of the concept is more important or the prescriptive rules on symbols...? OOP! Spoke too soon! Sorry guys.

[ctiebs]

@ 13:55 wouldn't it be the Vrain^2 as well? Also @blomman , do you think understanding of the concept is more important or the prescriptive rules on symbols...?

[fluff125]

At 12:00 I think this guy is wrong. You would catch the same amount of rain on your head per second no matter how fast you are going. The reason you catch less if you go faster is because you arrive in a shorter period of time.

Think about a moving sidewalk on the ground with one square region of the sidewalk painted white. If it is raining at the same rate everywhere, it wouldn't matter how fast the sidewalk went, it would catch the same amount of rain per second as everywhere else on earth.

[Slider68]

@fluff125 I don't know what happened to my first attempt at replying to you (I'll try again...). Both you and professor Lewin are correct. Cos(alpha)*sqrt(Vpm^2+Vrain^2) equals the vertical rain velocity. Approaching this from an X,Y component point of view instead of vector you end up with rain volume on head=Vrain*AB*D/Vpm and rain volume on front=AHD. So as long as standing upright while walking, the rain on front is constant and rain on head depends on your walking speed.

[fluff125]

@Slider68 No. The rain hits at a larger angle, it is true, but MORE rain is hitting you. Notice that when he draws the vectors (representing raindrops) slanted, the lines become closer together.

The way he tells it is misleading. No matter how fast you move, the same amount of rain hits the top of your head per second. If you move at 1/10 light speed, you will arrive very fast, so almost no rain will hit the top of your head.

This guy is good at math, but has very dim conceptual skills.

[Slider68]

@fluff125 You are still both correct and that includes professor Lewin. If you look at my component equations below you will see the D/Vpm term which equals the time it takes to move at a constant velocity (Vpm) a distance D. The rate of rain volume falling on your head (not considering the density of the rain) is the rain velocity (Vrain) multiplied by area (AB). No matter how fast you move the same total volume of "rain" intersects with the body from the front and you get ADH.

[Slider68]

@fluff125 Of course everything I came up with needs to be multpllied by the density of rain within a volume of air and again everything I calculated assumes the people are standing vertically. Note that since they are moving at a constant velocity and therefore it is difficult for them to be leaning forwards much so this is a reasonable assumption (yes the induced wind against them will cause them to lean forwards a little, but not much).

[MrWhatdoyoucare]

@fluff125 he never said you catch less rain, but rather he projected it so that he could be able to calcute the total amount of rain they would catch ! good eye though.. !

[blomman43]

Remarkable that an "expert" in physics does not know that the correct unit designation for seconds is "s" NOT "sec".

[TheUFOeffect]

WOW! this is one of those problems you understand when shown but asked to do it yourself you have no clue where to start.

[fullmetaljason]

Thank you I really appreciate the visual demo, great video.

[dowling1981]

@fullmetaljason Get them til fall?

[sperrepolken]

You can really see that he loves what he does. More teachers like this please!

[Cifrocco]

LOL, great ending line!

[Cifrocco]

Hey when was this video shot? Looks like a younger Professor Lewin than the famous MIT lectures. Cool!