Conservation of energy | Work and energy | Physics | Khan Academy

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Using the law of conservation of energy to see how potential energy is converted into kinetic energy. 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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[@Nuhjeea]

Love all your videos, but I wish you did slightly more complicated Physics examples! I'm in college and your calculus videos were very relevant and taught me a lot! Your physics videos definitely helps reinforce my knowledge but the examples are often much simpler than ones I have to tackle in class/exams, etc.

[@littledivergirl1105]

if all the students that actually learnt from this didn't go to class anymore all the teacher would have no class. this makes so much more sense than in the 1.5hr class i have

[@musicaldarpan629]

Lol.. did you passed your exam 😁😁

[@A591m]

because of these videos i'm gonna get an A on my exam bet

[@SamRobertduty]

You are very smart. I hope all lot of people learn from this video. I am in grade 10, doing physics 11 and I am trying to learn energy before the teacher gets to explain it. THANK YOU !!!!!

[@Jhayca0930]

i understand you better than my teacher...thank god your channel exist

[@SamLesCreations]

I LOST IT AT "IT CHANGES COLORS, TOO, AS IT FALLS!" OH MY GOSH 7:30

[@orchoose]

+Samara Lesage lol

[@orchoose]

UNIVERSAL GALAXY Depends on your definition of tracher,,, if it is someone who can pass knowledge in clear way, than he is a teacher, oposite to some ppl working in schools.

[@everythingyouneed7778]

gravity=9.8

[@shirajummunira5511]

Drama

[@Peter_1986]

+Lunar Moon The closest I have seen Sal come to a school teacher is probably when he has visited schools and answered questions from children during math classes. There are a few images like that on the Internet.

[@ordinary.salsabil]

Watching after 13 years is still good 👍

[@jeevacation]

this video is 11 years old........ feel old yet?

[@HiltyC]

I feel like this learning is somehow better than the "progressive education" that my school district provides, 𝐞𝐥𝐞𝐯𝐞𝐧 𝐲𝐞𝐚𝐫𝐬 𝐚𝐟𝐭𝐞𝐫 𝐭𝐡𝐢𝐬 𝐬𝐮𝐩𝐞𝐫𝐢𝐨𝐫 𝐞𝐱𝐩𝐥𝐚𝐧𝐚𝐭𝐢𝐨𝐧 𝐰𝐚𝐬 𝐫𝐞𝐜𝐨𝐫𝐝𝐞𝐝

[@mariaahmed1695]

I was 4

[@anonymousejones8742]

It’s 14 now , this was released when I was born 😭

[@lucass4827]

@@anonymousejones874216 now and we are the same age

[@h3sy]

Wow its almost 17 now

[@abdullahbineid4963]

even I dont speak English very well , I got it thanks a lot

[@abdallababikir4473]

تعلم انجليزي تستفيد

[@AnimeTheorysReddit]

stfu

[@alisuri6637]

Acha

[@taehpawgaw5590]

You make physics so much easier and understandable. I am starting to like physics.

[@Basic-Tron]

Great video man, thanks a lot!

[@akhan7535]

I honestly love Sal so much. Thank you!!! Wouldn't have gotten through class without your help

[@conve4521]

your a wonderful man. god bless your parents for creating you.

[@uheartbeast]

I love your vidoes! They are helping me so much.

[@diaverna]

HeartBeast Hello!!! I am a subbie :D

[@Munbo44]

You have saved my life. My friend and I have been trying to figure this out all week (teacher isn't there sometimes, and when he is we have work or something) and we have a quarterly test tomorrow. Thank you so much!! :D

[@nirmitbatavia8192]

Munbo44 all the best... Wait after 3 years. 😆😆😆

[@mewying5184]

@@nirmitbatavia8192 It's been three years now what

[@0dontspeak]

His voice is soothing. And he's GREAT at teaching! I understood it so well.

[@TehBigTMane]

Thanks for the videos! I was really lost on my homework so I decided to look for help and this is exactly what I needed.

[@jessynsiesi5443]

I finally understand the conservation of energy 🎉

[@odefeoberabor7597]

I love this. It was looking impossible in class, thanks so much man.

[@richard_darwin]

It's actually the simplest, yet most important law of physics

[@adeshcobra7543]

Lol normal lecturers complicates our lives 😂 😂 😂

[@SweetreatsbyGab]

I missed class for a field trip today. You’re a life saver

[@opmike343]

I swear, ALL college professors should be required to watch Khanacademy and PatrickJMT's videos before every stepping foot into a classroom. Too many of those guys (while VERY intelligent) have forgotten, or never learned, how to "teach".

[@musicaldarpan629]

Hii after 10 years 😁😁

[@megaericproductions8360]

Wow this video actually taught me, unlike the one hour lecture I attended from a dweeb with a PHD

[@chrisofnottingham]

Another way to state the consequence of this approach is; whatever the shape of the path which the object takes on its journey, its speed at any particular height is always the same. It's a shame that friction messes things up but in the world idealised ice slopes and perfect roller coasters I think its a really fascinating outcome.

[@h5348227]

your a life saver may allah give you a long life full of happines

[@The3nlightened0ne]

I've never seen anything as beautiful as mathematics

[@Peter_1986]

I have always found vector fields and graphs of polar coordinates to be incredibly beautiful. Vector fields have some very complex symmetric patterns, and polar graphs sometimes look almost like flowers.

[@alisuri6637]

Because you have not seen me

[@MrNintoku]

I don't care about the topic, I just find his voice so soothing.

[@CCxWudz]

This channel helped me pass my college physics class years ago. Thanks for all the knowledge

[@littledivergirl1105]

this man is honest to god a pure genius!

[@Ghost572]

glad you showed that example of an icey slide! made it even better

[@fahadalbalushi1602]

U do not know how much u have helped me, the a lot

[@JazzoFett]

THAT MARK AT 4:50 BOTTOM LEFT IS KILLING ME.

[@joey93282]

You made it so simple, and I'm able to apply this underlying knowledge to more complex problems. Thank you for helping me.

[@wombatpandaa9774]

4:34 anybody else bothered by the left corner? XD

[@zachcombs1288]

Thanks so much man, I have an ETA this week and I never really understood this process. This helped me so much!

[@mayad9963]

Thank god for khan academy !

[@jenkudos]

You explained it better than my lecturer ever could! Thank you :)

[@alisuri6637]

Your welcome

[@musicaldarpan629]

I am feeling like I am time traveling in past while reading so old comments 😁😁

[@NationalPro]

FASCINATING!

[@thebigdille]

so much more understandable now

[@rm130]

you make my life so much easier!

[@alisuri6637]

I told you not to take hard-core kode

[@alifarzanehfar]

It depends on the temperature of air. The reason a pendulum loses energy is that it collides with air molecules. The extra kinetic that is given to all those molecules is represented as heat. To calculate this, you can assume a block is moving in one direction at constant velocity.Depending on the area of the face of the block, it's momentum, air temperature (average velocity of air molecules) and pressure(how many there are) it can be calculated how much heat is given to the environment.

[@jyothia6770]

this video is almost as old as me yet better than what my lecturer teaches

[@TheHiddenSupremacy]

your content is actually perfect for IB

[@zvlhelme]

Really improved my understanding on this topic!

[@amalshafernando7993]

such a good teacher!

[@Bub-h6e]

I ALWAYS LOVE your videos, you speak well and have exceptional penmanship. BUT in the last few videos I have watched you are using a thicker font which makes everything hard to read, follow and understand.. PLEASE go back the the thinner font when writing so that it is easier to follow along and read!! Thanks

[@taevy12]

thank you sir, you are 100 times better than my professor :)

[@AnonymousHuman2.0]

This vid is almost as old as I am. The first people who watched this probably already got a 20k a month job.

[@TheQupus]

that speck left at is really bothering me...

[@DogeDELUX]

Glad I'm not the only one who thinks that!

[@malevip]

I wanted to punch my screen!! It was so irritating to see that one dot!!!!

[@KenzoKento]

+TheQupus Same omg I actually had to leave the vid lol

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#TeamOCD

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k

[@gasserhegazy1267]

THIS IS SOO GOOD

[@PewDiesBro279]

Thank you very much i wish you were my teacher!

[@jilwanrahimi8987]

Nice, don't get why people dislike your videos. Great work

[@VivianaDM]

My physics final tomorrow is about this. Thank you so much for explaining it!

[@musicaldarpan629]

Hey.. did u pass your exam?? 😁😁

[@surajinsha665]

i like that concept thanks sir

[@3Rton]

@3Rton I am not totally sure if this is correct but supposing that we want to know when the energies are exactly same it should work right?

[@jihad94elite]

Gravity pulls towards the Earth...he is dropping the box so gravity is downward therefore positive...hope that helped :)

[@armyrule0111]

thanks..easy to understand.

[@musicaldarpan629]

Did you passed your physics exam? 😁😂

[@honeypot11]

i just wanted to say thank-you for putting the time to make these videos for us. I think that you sound better than my physics teacher! lol and i laugh a bit at the little jokes you do xD and the shaky mouse sometimes (yes im weird) thanks again!

[@musicaldarpan629]

Heyy.. did u passed your exam?😁😁

[@marklee1194]

Thank you so much for your help.

[@adamaqmal]

God Bless uploader.

[@greekcuty66]

i so wish this guy was my teacher..

[@musicaldarpan629]

Did you passed your exam?😂😂😂

[@TuningAnApple]

@PeaceFighter2 I might be wrong, but calculate when the ball is at the peak of its trajectory (where the velocity is 0), and at that point find the distance of the peak from the ground (or bottom of cliff, where ever it's landing). With that you can calculate gravitational pot. energy. Then you can set initial potential energy + Kinetic energy equal to final potential + Kinetic energy and solve. At that point of energy you can use Energy = work = force x d and find distance. Force being mg.

[@alisuri6637]

Literally watch this from school

[@MrSoundhunter]

So good at explaining! Thanks Sal!

[@musicaldarpan629]

12 years ago 😁😁

[@TuningAnApple]

For you problem with the box being dropped on the crazy slope, since velocity is a vector, wouldn't it's direction affect PE and KE? It's direction seems to be changing constantly too. So, do we just ignore direction?

[@musicaldarpan629]

Hey did you passed your exam 😁😁😁

[@yalilboya]

Thank you for the videos !

[@bladervinay]

Great video as always from Mr Khan well explained

[@AnthonyVoutas]

@ninjaturtle205: Good Question. There is a force being applied to the box by the surface, because otherwise the box would fall straight through it. This is the "normal force" which is talked about earlier in the playlist. So the force accelerates the box, thus changing its velocity, but the work done by the surface is assumed to be negligible, so the kinetic energy doesn't change, which means that the velocity changes in direction only, but I'm not entirely sure why it's negligible.

[@musicaldarpan629]

Did u get your answer?😁

[@Sutto3721]

Previously he said it's assumed to be 10m/(s)^2 just for the sake of easy calculations. Gravity, however, differs from place to place (even on earth)...places such as the north pole will be much different. But usually as a constant (the level of physics we're doing) we have the average of gravity as 9.81m/s^2, for simplicity sake.

[@shivavishnu9984]

Thank you for your effort for teaching sir

[@AidenGonsalves]

man's really tryna save my semester eh

[@Grandbox1992]

Thanks a alot ...

[@adriankhoury921]

Thank you ☺️

[@gold_455]

thank you so much !!!

[@drorharush]

Thank you.

[@aena_]

Thanks alot

[@bisharalol]

"I WILL SEE YOU IN THE NEXT VIDEO" *you never actually see us :( *

[@malkisehgal2481]

Hi there. How are you 10 years later!?

[@siyayas9134]

@@malkisehgal2481 hey there how are u 4 months later

[@jerryd2243]

​@@siyayas9134 hey there how are u 2 days later

[@comicbest2662]

1month later😎

[@musicaldarpan629]

@@comicbest2662 9 months later 😁

[@aena_]

Very useful

[@ChristopherChibaite]

GOOD WORK I LIKE IT

[@Dyanahhhful]

Just want to let you know that you are AWESOME and HIGHLY APPRECIATED! :D

[@ishan0369]

Great!!

[@thesovereignonion2283]

is good thank you

[@fruitpluslegumes]

Sorry if this is an unnecessary question however it has been bothering me. Since in a given condition (Ex. pendulum swings from Point A to Point B) some of the energy is lost to sound or air resistance. I asked a teacher if there is a constant that represents conversion of energy into sound, thermal, due to air resistance and was told that the knowledge was beyond high school physics. DOES ANYBODY KNOW THIS EQUATION THAT INCORPORATES THE CONVERSION OF KE or PE into heat, sound, etc/ the concept?

[@calebbauer3739]

Gave this video a like because why not

[@abhishikthmatta366]

really helpfull

[@alifarzanehfar]

Also, you should be able to do some of those calculations, assuming you know the ideal gas law and are familiar with integrals.

[@LauraSouza-vw4ml]

sal khan is my religion

[@jewbinson]

@TuningAnApple Yes. Energy is a scalar, not a vector.

[@8bit_pineapple]

It also changes colour when it falls :D

[@musicaldarpan629]

Hii..after 11 years 😁

[@8bit_pineapple]

@@musicaldarpan629 hi

[@8bit_pineapple]

@@musicaldarpan629 You edited out the kissing face lol 😘

[@lemonade_tara7429]

I feel that it's actually not always true in the example of the object rolling down the hill as some of the GPE must have transferred to heat energy as well owing to the friction acting upon the object.

[@pyLz]

Nice video, but I wonder to what extent the conservation of momentum is affecting your result (the slope is being pushed to the left).

[@leenukes7418]

Thanks bro

[@gurkis35]

What are you talking about? Potential energy and Kinetical energy are not always equal. Its the summ of Ep and Ek that stays constant. For example Ep+Ek = const.

[@niconikko]

This was the first time I saw teacher khan used a rectangle to draw a box.... In the other videos, he preferred drawing by pencil

[@ToastFroEva]

THANK. YOU.

[@musicaldarpan629]

Hii after 12 years 😁

[@Surfurplex]

You should be more consistent giving your answers with the correct amount of digits; the answer in the first example isn't 100 J, it's 0,1 kJ because you gave the mass with only one digit, which really means that the mass can be anywhere from 0.5 kg to 1.4 kg (adds an uncertainty which must be accounted for in the answer). I know it seems pointless, but some teachers put a lot of weight on this.

[@MarylandDevin]

Question: Why would you use this formula if you could use V^2=Vi^2+2ax? V^2=0+2(9.8)10, V=14m/s Seems easier. Could You show me another example where it might make more sense to choose an energy formula instead of velocity?

[@atobos282]

Perhaps if there's a mass involved. Energy formulas may be needed

[@dialasaab972]

can you explain the formula or P.E+K.E+U?. which is change on potential E and change in kinetic E added to change in internal energy? what does the internal energy change, and how to solve for it?

[@musicaldarpan629]

Did u passed your exam?😁😁

[@keen125]

Wow!

[@b3a3n3a3n3a3s]

09:27 - This probably sounds stupid but you multiply both sides by 2 because it's x 1/2 right? Why didn't we do that in the first example though? It was just 1/2 m vsquared = 100J. and then 1/2 vsquared = 100J. Why was the mass insignificant then (because it was one) but not now?