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

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

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16 жыл бұрын

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More on work. Introduction to Kinetic and Potential Energies. Created by Sal Khan.
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Physics on Khan Academy: Physics is the study of the basic principles that govern the physical world around us. We'll start by looking at motion itself. Then, we'll learn about forces, momentum, energy, and other concepts in lots of different physical situations. To get the most out of physics, you'll need a solid understanding of algebra and a basic understanding of trigonometry.
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Пікірлер: 165

@bleh4546 6 жыл бұрын

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 5 жыл бұрын

same

@bgregz 5 жыл бұрын

yup

@phillipdhanpauliii3857 5 жыл бұрын

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

@kaizen3876 4 жыл бұрын

@patinho5589 4 жыл бұрын

bleh it’s emotions

@ramyaprabhu6625 6 жыл бұрын

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🙏🙏🙏🙏

@HisCarlnessI 10 жыл бұрын

Watching this right before my final XD

@nirmitbatavia8192 6 жыл бұрын

HisRoyalCarlness same here 6th grade final.

@axelbergiers2339 6 жыл бұрын

Feel you bro

@musicaldarpan629 3 жыл бұрын

Did you pass??

@HisCarlnessI 3 жыл бұрын

@@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 3 жыл бұрын

@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.

@LightningBoyNation 7 жыл бұрын

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

@brisk483 5 жыл бұрын

AGREED

@swiftingstar 10 жыл бұрын

That cliff hanger at the end...

@matthewmueller8726 6 жыл бұрын

Sal you should do ASMR about physics

@hiccuphadock5059 8 жыл бұрын

sal's videos are just fun to watch.

@jayshreeakhouri795 5 жыл бұрын

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

@TheBigBanggggg 6 жыл бұрын

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

@VitiV 7 жыл бұрын

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 7 жыл бұрын

layman's terms ;)

@VitiV 7 жыл бұрын

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

@rihamission487 Жыл бұрын

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

@llllaarr2518 11 жыл бұрын

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

@yadgar1735 4 жыл бұрын

Laura Levy sooo how did you do? 😂

@raphandgaming4590 2 жыл бұрын

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

@dotted_stains2792 Жыл бұрын

@@raphandgaming4590 DUDE WHA-?

@chelseamaharaj1384 10 жыл бұрын

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

@Dotrade 8 жыл бұрын

+Chelsea Maharaj love u

@dorol6375 2 жыл бұрын

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 Жыл бұрын

What's the channel's name, pls share

@vincetheworldly537 13 жыл бұрын

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

@rogertiger 14 жыл бұрын

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

@mucyochristian3877 4 жыл бұрын

Thanks guys i really give much credit for your amazing tutorials

@ttkid100 12 жыл бұрын

YOU ARE AWESOME!

@brvheavyhitter20 15 жыл бұрын

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

@elitegence 13 жыл бұрын

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

@miguelvaldez4901 5 жыл бұрын

Wow fantastic

@osama2almousallam 6 жыл бұрын

6:09 IT'S OVER 9000!

@oluwasefunmioluyede2352 10 жыл бұрын

well done sir

@spectrum792 5 жыл бұрын

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 5 жыл бұрын

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 4 жыл бұрын

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 4 жыл бұрын

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.

@caseypena420 15 жыл бұрын

Thanks dude, great videos!!!

@a.h_xvry2118 2 жыл бұрын

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

@rabalac99 13 жыл бұрын

@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

@alisuri6637 4 жыл бұрын

Brillaint

@nipunparadkar9458 11 жыл бұрын

Thanks........

@TheViper346 12 жыл бұрын

Awesome

@woodenjaw 15 жыл бұрын

I concur!

@chandabembachalwe8864 3 жыл бұрын

What is the SI unit for mass?

@shawnk01 11 жыл бұрын

thanks man

@kachingaaa 10 жыл бұрын

I love you Sal

@jossell911 10 жыл бұрын

Thanks

@liquidfatty394 6 жыл бұрын

nicd work how foes relate to power

@arfan631 3 жыл бұрын

u cant type. N I C E!

@saalaxibrahim9508 8 жыл бұрын

thanks for your explanation

@fafase 13 жыл бұрын

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.

@bijayaghosh5158 7 жыл бұрын

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

@Peter_1986 11 жыл бұрын

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 3 жыл бұрын

Exactly 😂

@bmgag19 13 жыл бұрын

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 3 жыл бұрын

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..

@monaegr 15 жыл бұрын

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

@stfrankies240 12 жыл бұрын

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

@RanveerSingh-sv9co Жыл бұрын

Same

@SamRobertduty 16 жыл бұрын

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

@alisuri6637 4 жыл бұрын

Nhi karo yaar..... sach mein

@jesusngomonchama1630 8 жыл бұрын

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

@denzelalvarez2972 6 жыл бұрын

So what's the formula for energy?!

@simpledudeskies 11 жыл бұрын

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

@giulialeo8 12 жыл бұрын

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

@alisuri6637 4 жыл бұрын

I got F haha better than yours loser

@musicaldarpan629 3 жыл бұрын

@@alisuri6637 sawage reply dude 😂😂😂🤘🏻

@alisuri6637 3 жыл бұрын

@@musicaldarpan629 thnks lol

@Evenstephenss 13 жыл бұрын

Where is part 3?

@otuonyec 14 жыл бұрын

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 Жыл бұрын

I'm just curious what do you do now

@thestudylobby7648 11 жыл бұрын

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 :).

@IvanChavez-es7yy 7 жыл бұрын

Watching this during my final...

@abdallababikir4473 5 жыл бұрын

You're allowed a phone during an exam? Lucky

@maryam-qh8sj 6 жыл бұрын

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

@piyush4left 13 жыл бұрын

awesome knowledge source

@vincetheworldly537 13 жыл бұрын

@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?

@godandtechnodude 11 жыл бұрын

98000

@xlwaiyiplx 15 жыл бұрын

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

@kabouch 4 жыл бұрын

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.

@honeypot11 15 жыл бұрын

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 3 жыл бұрын

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

@Chantheman5 13 жыл бұрын

I loveit how every video from khan academy has 6 dislikes

@musicaldarpan629 3 жыл бұрын

Now 66 😂

@TheGamingWattsit 5 жыл бұрын

Why is it from rest?

@AverageJoe8686 14 жыл бұрын

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.

@CheeseGrater601 11 жыл бұрын

Oh dear

@PrashantMohta 13 жыл бұрын

i said that 2 times LOL :D cooooooool vid

@alisuri6637 4 жыл бұрын

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

@wcsummer 14 жыл бұрын

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

@Drakor65 9 жыл бұрын

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 9 жыл бұрын

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

@izzystreaks1807 9 жыл бұрын

.. no, the correct unit is kg.

@agent475816 8 жыл бұрын

+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.

@miraslam2000 12 жыл бұрын

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

@sobiakashif2355 4 жыл бұрын

How do we say ; W=MGH

@alisuri6637 4 жыл бұрын

W=MGH Is said like Sonia Kashif

@MattMahael 12 жыл бұрын

@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.

@kairanadotoe22 13 жыл бұрын

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

@musicaldarpan629 3 жыл бұрын

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 😳😂🤘🏻

@kairanadotoe22 13 жыл бұрын

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

@fuzzyhunty 13 жыл бұрын

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

@cspower12 12 жыл бұрын

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

@amirashoury783 7 жыл бұрын

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 7 жыл бұрын

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 7 жыл бұрын

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 7 жыл бұрын

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 6 жыл бұрын

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 6 жыл бұрын

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.

@benjoandrichie 15 жыл бұрын

9.8

@musicaldarpan629 3 жыл бұрын

😳11 years ago...

@raph0renzoo 12 жыл бұрын

right?

@saadalshlowiy1060 3 жыл бұрын

who s from 2021?

@musicaldarpan629 3 жыл бұрын

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

@vixtriestodowellinschoolep8323 Жыл бұрын

the video was 13 years old when you posted this, cut him some slack 🤧

@subhanbokhari7132 6 жыл бұрын

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

@abdallababikir4473 5 жыл бұрын

He said approximately...

@alisuri6637 4 жыл бұрын

Idiot he said approximately

@adamaqmal 12 жыл бұрын

headache

@alisuri6637 4 жыл бұрын

Yah you are a headache

@basmaeidarous16 9 жыл бұрын

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

@DBZeenX 9 жыл бұрын

basma eidarous Not to me.

@JPxKillz 8 жыл бұрын

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

@Idkidkidkidkidkikikidkidkidk 8 жыл бұрын

+Julien JP savage

@basmaeidarous16 8 жыл бұрын

Julien JP Thanks.

@bluuman1 7 жыл бұрын

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.