Work and energy (part 2) | Work and energy | Physics | Khan Academy

[@bleh4546]

I actually started crying while I was watching this like idk why I can’t focus on anything and it’s stressing me out

[@Shay-su6le]

same

[@bgregz]

yup

[@phillipdhanpauliii3857]

Tell your doctor, you may have ADHD. I have been on the same boat.

[@kaizen3876]

Ok

[@patinho5589]

bleh it’s emotions

[@ramyaprabhu6625]

From all students all over the world, Thank you for making our lives much easier. Scientists might be inventing and discovering different things everyday but it is of no use if it cannot be passed on to students in a way that they understand. Thank you once again🙏🙏🙏🙏

[@LightningBoyNation]

Wow! An entire 240p Just for me to enjoy!

[@brisk483]

AGREED

[@HisCarlnessI]

Watching this right before my final XD

[@nirmitbatavia8192]

HisRoyalCarlness same here 6th grade final.

[@axelbergiers2339]

Feel you bro

[@musicaldarpan629]

Did you pass??

[@HisCarlnessI]

@@musicaldarpan629 oh man probably. That was right after my Highschool sweetheart left me and I was super depressed. But weirdly the only thing I could focus on was school and got straight 4.0s that quarter.

[@HisCarlnessI]

@Armand Ciowela I'm a custodian. But union. So like, $21/hr and great benefits. In a much better place than previous years mentally too.

[@matthewmueller8726]

Sal you should do ASMR about physics

[@hiccuphadock5059]

sal's videos are just fun to watch.

[@VitiV]

Khan, I love you. I am in this unit in honors physics (junior in high school). My teacher never chugs equations and you put everything in such lamence terms that I feel right in line with this unit now. Thanks!

[@neelsvanwyk1832]

layman's terms ;)

[@VitiV]

Neels van Wyk aye, only used it in speaking before this. Thanks for the heads up

[@swiftingstar]

That cliff hanger at the end...

[@rihamission487]

Once again Khan Academy saves the day. Thanks a lot, Sal. Love from your country, Bangladesh.

[@llllaarr2518]

Just so you know, this is the only reason I'm not going to fail this test tomorrow. Thank you so much :)

[@yadgar1735]

Laura Levy sooo how did you do? 😂

[@raphandgaming4590]

@@yadgar1735 it’s been 8 years, I think she died

[@Gtwiwhwidyjw_2792]

@@raphandgaming4590 DUDE WHA-?

[@TheBigBanggggg]

WORK is the CHANGE in kinetic energy. It's been long Sal went to school.

[@dorol6375]

I've been binge watching all of these before going to high school It's been pretty fun I'm going to electrical engineering too so I'll watch that Previously I just watched all the concepts but not the equations, after I finish this whole playlist I'll listen to a different channel I heard about but can't remember the name of rn that goes more in depth

[@RanveerSingh-sv9co]

What's the channel's name, pls share

[@chelseamaharaj1384]

Thanks so much sal ^--^ these vids are helping me with revision for cxc exams and im actually understanding everything better

[@Dotrade]

+Chelsea Maharaj love u

[@enanxahmed]

Even if the velocity is constant, the elevator is moving upwards thus having a vertical displacement. And to make that happen the pulley is applying some force on the elevator. As Displacement is happening due to Force here, Work is being done. And if the net force is 0, means if the force gravity is pulling it with the same force downwards, it won't move upwards and the force will be balanced. So, the pulley must be pulling on the elevator exerting a greater force than that of gravity to make the force imbalanced hence making the elevator move upwards. So, even at a constant velocity against gravity, the net force can't be zero; as the pulley needs to keep working with a greater force than that of gravity to maintain the constant velocity, thus making the vertical displacement possible.

[@yassinfouad8447]

I was confused about this point too so I thought there is initial velocity then he said the elevator stops at 100m and that is impossible cuz it is supposed to continue moving with constant velocity if there is not an external force. so me too I dont understand how the elevator is moving if the two forces are equal cuz this is a case of balance.

[@patinho5589]

I’ll explain to both of you: Am initial force had to be applied to the elector greater than that of gravity to ACCELERATE IT. Initially. For maybe a tiny bit of time. Say a second. Then let’s reduce that force now to EQUAL gravity. NOW the forces are equal. But the elevator is already moving. Remember net force of 0 does NOT mean things aren’t moving. It means things for not ACCELERATING. And object with net force 0 on it will continue to move with its same velocity for ever (think of it being in the vacuum of space. On Earth wind resistance and friction means we always have forces against us) . Ok.. so now the elevator is moving (after the first seeding) and we are considering the work down from then. We aren’t considering the acceleration part, or the deceleration part.

[@patinho5589]

Spectrum remember that constant velocity IMPLIES that the net forces MUST BE Zero. You need to get this part solid first. ON EARTH we apply forces to cars and stuff at a constant velocity to GET to net forces of zero once wind resistance and friction are taken into account.

[@rogertiger]

It has to do with diferential and integral calculus. Force as a conservative vector field is equal to minus de gradient of the field. On the other side, is the Integral of F dx. Being a definite integral and with the gauss divergence theorem, they are equal and will be what you said! beautiful :D

[@jayshreeakhouri795]

take a sip everytime he says "I don't know"

[@vincetheworldly537]

4:30 sniff! hehe. i also have a cold when i first watched this. got it. now i'm ready for tomorrow's report.

[@SamRobertduty]

I like your teachings a lot ! You should become a professor !

[@alisuri6637]

Nhi karo yaar..... sach mein

[@magicman_oo1]

They ususally specify......or u can just ask the teacher..its not that complicated...if u dont know just ask since both is sometimes used like Sal did. In physics the BEST thing to do would be to use 9.81...while in Mechanics in math, the BEST one would be 10.....These are what is almost always used for each subject...but just ask to make sure.

[@Bridgetl-_-l]

I'm just curious what do you do now

[@mucyochristian3877]

Thanks guys i really give much credit for your amazing tutorials

[@fafase]

for the sake of this world and next generations to come, you should join forces and work with PatrickJMT and Derek Owens to create the perfect and ultimate math and physic encyclopedia.

[@bmgag19]

so, you said it takes the elevator a force of mg to counteract gravity and move up a certain distance. but doesn't it take more than mg. In other words, if it just doesnt move, doesnt that mean the elevator is in equilibrium? I would think that it would require more force than mg to move up.

[@musicaldarpan629]

Replying after 10 years 😂 Yes , to be in equilibrium , it required exactly equal force as mg , but to move up it requires slightly more than mg.. hope u got that , 🙂.. Btw.. what r u doing nowadays 😅just asking..

[@elitegence]

@gpak47 Gravity is pulling downwards on the object which means more work to make the elevator go upward.

[@giulialeo8]

Thank you!!! It really helped! I got a B on the work and energy test!

[@alisuri6637]

I got F haha better than yours loser

[@musicaldarpan629]

@@alisuri6637 sawage reply dude 😂😂😂🤘🏻

[@alisuri6637]

@@musicaldarpan629 thnks lol

[@brvheavyhitter20]

THANK YOU!!! the eqn for gravitational potential energy makes sense now!!

[@osama2almousallam]

6:09 IT'S OVER 9000!

[@miguelvaldez4901]

Wow fantastic

[@simpledudeskies]

WOW!!! NO REASON WHY NOT TO SUBSCRIBE! THESE PEOPLE ARE SO AWESOME!

[@ttkid100]

YOU ARE AWESOME!

[@rabalac99]

@Calilifestyle89 thats so true cuz i started physics last year and that teacher just did equations without explaining and now im in my second year with a new teacher who is trying but its not working...and its torture for the students and the teacher but its his job to teach so

[@Peter_1986]

I guess you could say that energy was "created" by the Big Bang. But not even that is entirely true, because time itself was created during that event.

[@musicaldarpan629]

Exactly 😂

[@caseypena420]

Thanks dude, great videos!!!

[@a.h_xvry2118]

Its been 12 years since you commented this hows life dude ?

[@alisuri6637]

Brillaint

[@nipunparadkar9458]

Thanks........

[@woodenjaw]

I concur!

[@oluwasefunmioluyede2352]

well done sir

[@xlwaiyiplx]

9.8. he used 10 cuz he wanted to simplify the calculation, since he didnt want to use the calculator all the time.

[@stfrankies240]

i cant thank u enough khan.also i love that way you always say I DONT KNOW and u know...lol

[@RanveerSingh-sv9co]

Same

[@saalaxibrahim9508]

thanks for your explanation

[@honeypot11]

heres a potential energy problem (gr. 11 physics): a man decides to climb an office tower using the stairs. if the floors are 3.8m apart, how much gravitation potential energy would the man have relative to the ground floor if he made it to the fifth floor? (i cant get this because it doesnt state his mass, is there still a way of solving?...something to ponder)

[@musicaldarpan629]

12 years ago 😳😳.. Btw, you got it's answer?😅😂

[@shawnk01]

thanks man

[@vincetheworldly537]

@bmgag19 uhm yeah, if the upward force is the same with the downward force it musnt be moving... uhm, did you figure this out already? i mean, do u already know the answer to your own question?

[@jossell911]

Thanks

[@TheViper346]

Awesome

[@kachingaaa]

I love you Sal

[@liquidfatty394]

nicd work how foes relate to power

[@arfan631]

u cant type. N I C E!

[@wcsummer]

ΔPE+ΔKE=0 so ΔPE=-ΔKE If PE decreases, then KE increases and vice versa.

[@AverageJoe8686]

Sal (or anybody that knows), I would REALLY appreciate it if you could explain W(other) = /\KE + /\PE. It's not in my physics book (Shaum's Outlines: Physics, 10th) and my physics professor said you can't algebraically derive it and this is driving me crazy. It really seems like it should be [Epsilon]W for the Free Body Diagram but he said this isn't true, and didn't care to elaborate.

[@chandabembachalwe8864]

What is the SI unit for mass?

[@dailyphonix2325]

Kg

[@IvanChavez-es7yy]

Watching this during my final...

[@abdallababikir4473]

You're allowed a phone during an exam? Lucky

[@monaegr]

OMG i didtn get that one either! how r u supposed to get the answer if you dont know the mass?!

[@Chantheman5]

I loveit how every video from khan academy has 6 dislikes

[@musicaldarpan629]

Now 66 😂

[@piyush4left]

awesome knowledge source

[@thestudylobby7648]

Hey if you're looking for HW HELP ASAP, visit the thestudylobby. com Ask any question; we guarantee a response within 30 minutes!! Give us a try and a thumbs up if we were able to help you out :).

[@denzelalvarez2972]

So what's the formula for energy?!

[@Drakor65]

wait a minute shouldn't he have converted the kg into grams and then plugged it into the equation or at least said that the PE was in kJ^-1

[@anao9765]

I might be wrong but i think the reason he didnt do it is because kg is the SI unit for mass

[@izzystreaks1807]

.. no, the correct unit is kg.

[@agent475816]

+mehmet holbert No, a definition of a newton is Kg . m/s2 you have to use those units kg for mass, meters for distance, and seconds for time.

[@maryam-qh8sj]

shouldn't the gravity be negative ??? they have an opposite direction.

[@jesusngomonchama1630]

im not asking for work, please i need help for energy plus examples

[@miraslam2000]

@nihaldivyam let's see how well you could write on paint tool

[@bijayaghosh5158]

Does this principle of calculation of energy is applicable to the internal work-- work of walking, running or swimming?

[@kabouch]

An object resting on the ground with a constant velocity of 0m/s; consequently, the net force being applied on it is Zero N. I'd think that the object is under the downward gravitational force (-mg) and the balancing upward normal force (+mg), both are on the y-axis and they cancel each other so that the net force on y-axis is zero. Why should I apply a force larger than mg to lift it up. It seems intuitive for me that any applied force, regardless of its magnitude and direction, would net out and cause an acceleration.

[@godandtechnodude]

98000

[@MattMahael]

@kairanadotoe22 Yeah, theoretically it does because if you dug a hole under someone they would fall. Because gravity is always acting on you, and because the earth is always applying a normal force on your body, you always contain potential energy. I suppose if you lived on a planet with a mass smaller than yours, then you wouldn't contain potential energy, but on earth you do.

[@TheGamingWattsit]

Why is it from rest?

[@cspower12]

@nihaldivyam as long as you understand what he's teaching you, his handwriting shouldn't be a problem.

[@sobiakashif2355]

How do we say ; W=MGH

[@alisuri6637]

W=MGH Is said like Sonia Kashif

[@kairanadotoe22]

And one more thing.... are you saying that a body contains potential energy when its in a state of rest?

[@musicaldarpan629]

Exactly.. potential energy is a stored form of energy..so it can be at rest .. Example a body is rest at a height of 10 metre has gravitational potential energy stored in it...😅😅 Replied 9 years ago 😳😂🤘🏻

[@CheeseGrater601]

Oh dear

[@Evenstephenss]

Where is part 3?

[@benjoandrichie]

9.8

[@musicaldarpan629]

😳11 years ago...

[@kairanadotoe22]

but isnt g taken as negative or something since the body moves against gravity..so therefore the ans becomes negative?

[@PrashantMohta]

i said that 2 times LOL :D cooooooool vid

[@alisuri6637]

Just Trina be cool Han................1D10T.

[@amirashoury783]

sorry but if there is no acceleration (constant speed) doesn't it mean there is no force (f =ma) and therefore there wouldn't be work???

[@neelsvanwyk1832]

Acceleration is not constant speed. Acceleration is an increase in speed. So if the object maintains its speed, then no work is done (Like an asteroid drifting away into space).

[@mousaalsaeed9410]

amir ashoury the net work is equal zero in this case but the work done by tension is equal this tention×upward distance

[@Nothing_serious]

Net force is zero but not the force you applied. Gravity exerts a force and since net force is zero therefore you exerted a force equal to gravity

[@shamikbera6095]

amir ashoury see there is a brief acceleration.Though Acceleration is zero but the forces acting on sums up to zero.Which means that body starts with some acceleration and comes to rest.( zero acceleration) .So the constant velocity is from the kinetic energy provided from previous force.

[@ruskodudesko9679]

you can apply a force to an object while still having the net force be zero. apply F1 to the right and the object starts moving, apply the same force to the left (while still applying F1) and the object will continue to moving with constant velocity, while the net force is zero - so no acceleration but still applied forces.

[@raph0renzoo]

right?

[@fuzzyhunty]

Next Video: /watch?v=kw_4Loo1HR4&feature=fvwrel its named Conservation of energy not part 3

[@subhanbokhari7132]

Isn’t the answer wrong at 1:52 it is not 125n it is 122.5n

[@abdallababikir4473]

He said approximately...

[@alisuri6637]

Idiot he said approximately

[@saadalshlowiy1060]

who s from 2021?

[@basmaeidarous16]

this is extremely confusing... your explanation is all over the place

[@DBZeenX]

basma eidarous Not to me.

[@JPxKillz]

+basma eidarous I think your IQ is just too low to handle the content.

[@Idkidkidkidkidkikikidkidkidk]

+Julien JP savage

[@basmaeidarous16]

Julien JP Thanks.

[@bluuman1]

Agreed that it is not the most well structured video. But the concepts are all there, and if you rewind the video you will probably be able to understand.

[@SickOfSillyPeople]

@DeloresTBH you do know what approximately means, right?

[@musicaldarpan629]

Why video quality is limited to 240p only😢 My 4K phone screen be like* am I joke to you?

[@adamaqmal]

headache

[@alisuri6637]

Yah you are a headache

[@tekal85]

only good thing is: i didnt pay you money for this lousy explanation.

[@DivyamAzad]

improve your handwriting dude

[@alisuri6637]

IDI0T he's writing using a mouse

[@musicaldarpan629]

😂😂😂😂😂😂😂😂😂😂😂🤣🤣🤣🤣

[@yolarola6261]

am I the only person who cannot stand this guy s voice

[@musicaldarpan629]

I am also here 😂😂😂🤘🏻🤘🏻

[@musicaldarpan629]

It's handwriting is also so confusing 😂