Nice reintroduction to the Lagrangian - it's been 50 years since I played with this.
@rohitjha86263 жыл бұрын
Still beautiful! isn't it?
@richardrigling49063 жыл бұрын
@@rohitjha8626 Yep!
@richardrigling49063 жыл бұрын
As you were going through the derivation, i could hear my classical mechanics professor's voice. Ghost from 50 years ago. Fascinating - to quote a certain Vulcan
@randomdude91353 жыл бұрын
So u never used it in 50yrs??
@randomdude91353 жыл бұрын
What's the purpose of knowledge is u rnt gonna use it?
@RodrigodaMotta3 жыл бұрын
In my first year in physics 1 course, my teacher tried to give an overview on Lagrangian Mechanics, but he used a lot math tools that i didn't know at the time, for exemple a Taylor Series with two variables. So, I don't need to say that i didn't get anything that he said. But your video can give a very good overview of Lagrangian for a first year!. Good Job! I want a Series!
@beoptimistic58533 жыл бұрын
kzbin.info/www/bejne/joGmmHqKbqefqLM 👍💐
@suddhasattasaha47932 жыл бұрын
Hey, if you want a complete course on Lagrangian Mechanics ( with problem solving sessions) , then here I am sharing a playlist with you, I created this series of videos to introduce LAGRANGIAN mechanics in a simple and exciting way, yet retaining the rigour of the subject. Hope you enjoy it ! THIS IS THE LINK TO MY PLAYLIST : kzbin.info/aero/PLZumX0a4ZsO0MSJ5Qujht8TOxm-w5XbBf
@fredg83283 жыл бұрын
In french "kinetic energy" is "énergie cinétique". There is no "T" in that. But it could come from the word "travail" which means "work" in french.
@joaovitorjungblut5225 Жыл бұрын
of course there is a 't,' it is right there: cineTique
@HakingMC Жыл бұрын
I thought it’s because T is before U, so they used T.
@CliffSedge-nu5fv9 ай бұрын
Whenever I see T used for kinetic, I usually also see V for potential. In Newtonian physics, U is used for potential and K for kinetic. V is used for electric potential per unit charge (voltage), so I appreciate the U to avoid that confusion. I still prefer K for kinetic, as T is often used for time period or for tension, depending on context.
@cmmaslanka9 ай бұрын
Exactly. Travail mécanique...
@Xaver_448 ай бұрын
I always assumed it came from the word for work in European languages, which mostly start with "T", because there is a theorem that states that the total work is equal to variation of kinetic energy
@davicruzpestana73293 жыл бұрын
Really cool! I'm planning on getting a Physics degree and this just keeps me motivated.
@bockminster74743 жыл бұрын
Don’t do it until covid is cured. Trust me I’m dying
@beoptimistic58533 жыл бұрын
kzbin.info/www/bejne/joGmmHqKbqefqLM 👍💐
@moldysnek3 жыл бұрын
@@bockminster7474 glad to know I'm not alone xd
@nurfitriyanaazizah34083 жыл бұрын
just don't
@DrAtomics3 жыл бұрын
@@bockminster7474 Facts man, me too... What year are you? (Senior coming into Fall semester for me). Things have been super tough during COVID
@lookthesky96322 жыл бұрын
After watching you video, I felt Lagrangian mechanics is a very smart way to do it. This feeling is like there is a house, front door is closed. Backdoor is opened but people don't know there has a back door in this house. When try to open the door and into the house, Newtonian mechanics try very hard use force to breaching the door, and Lagrangian mechanics just into the house from back door.
@user-lb1ib8rz4h2 жыл бұрын
maths and even problem solving in general is poking on all sides until you see some give. then poke there more, rinse, repeat. and if you see similarities to another house, then it makes things even easier ofc every problems has tools that make it easier or harder. but often, differentiation is much easier than integration, hence the Lagrangian comes in handy.
@dybydx31 Жыл бұрын
Absolutely right
@CliffSedge-nu5fv9 ай бұрын
Or can use brute force computational physics and take all the nails and bolts out and lift off the roof.
@ysailokesh3 жыл бұрын
Your teaching levels of physics is very good and it makes me to listen to your teaching
@droher13443 жыл бұрын
This is amazing man. I've always had a lot of problems with parametrization, and although that was not the core of the video you made me see it in a different way. Keep it up
@GalileanInvariance3 жыл бұрын
Nice introduction to LM ... An important point which was overlooked is the way in which LM can incorporate generalized forces (which would appear as extra terms in the E-L equation). Such forces must be taken into account when some physical forces acting on the system are not conservative (and therefore not expressible via potential energy). Such forces also are especially convenient/useful for assessing relevant constraint forces.
@donnymcjonny653110 ай бұрын
This is such a great breakdown of what's going on. I'm in a 700 level mechanics course and this is pretty much on par with what we've been reading (Goldstein)
@kingplunger60339 ай бұрын
700 level ?
@ramsey558 ай бұрын
@@kingplunger6033grad school
@jiaxinl40362 жыл бұрын
Thank you so much for posting this! The explanation is super clear and very helpful for me to understand this topic which is entirely new to me!
@scar60733 жыл бұрын
Please keep making videos on Lagrangian mechanics 🙏
@DotPhysics3 жыл бұрын
you know it.
@amirpasagic1623 жыл бұрын
For people that can't simply get over using the equation without knowing where did it come from (god knows I can't), video from Eugen Khutoryansky gives a rather satisfying explanation of Euler-Lagrange equation derivation.
@SolidSiren Жыл бұрын
I can't let it go ever in any instance. I can't shutup and calculate. I need to know the derivation, and why, and how, and inside and out. How else will I fundamentally understand the things I'm doing?
@amirpasagic162 Жыл бұрын
@@SolidSiren I feel you brother. That is why I warmly recommend this one. Also 'Physics with Eliot' channel has amazing resources on this.
@abhishekchatterjee71843 жыл бұрын
This was a really good video, Physics is very interesting subject, although a little complicated.
@kamalenduhaldar58053 жыл бұрын
Every indian jee adv aspirant is kinda junior physicist lol... (me😭)
@knotoftime96802 жыл бұрын
@@kamalenduhaldar5805 🗿
@khushilalit65512 жыл бұрын
I wonder sometimes, how can something be explained this good. Thanksssss
@DotPhysics2 жыл бұрын
Oh. That’s nice. Thanks!!
@physicsiseverything15 Жыл бұрын
T can be calculated- using resolution of vectors resolute T in vectors components as Tcosx (theta=x) and Tsinx. Tcosx and mg gets neutralized and we are left with Tsinx. Since, bob is moving in circular trajectory it implies we can equate Tsinx= mR(dx/dt)^2 where R is radius Therefore,. T= mR(dx/dt)^2/sinx
@pensivist Жыл бұрын
At 13:14, the derivative should be positive because you defined y as -l*cos(theta). Although it doesn't affect the result as you are squaring it later!
@tbatlas72432 жыл бұрын
This video is really helpful, but I think the diagram at 4:45 could use a redraw of sorts ;)
@DotPhysics2 жыл бұрын
I finally get this comment. I feel stupid now.
@bwm712 жыл бұрын
In your final solution for the pendulum problem you have upper case L in the denominator. It should be lower case.
@tornjak0963 жыл бұрын
should the y_double_dot on 10:37 be minus g because it is acting downwards or I am missing something
@Vaderphobia3 жыл бұрын
You are right 👍🏽
@user_27933 жыл бұрын
Yep
@Jacked_R_Us3 жыл бұрын
ye its -g
@remavas70762 жыл бұрын
He lost a minus when solving the last equation.
@piotrbiy87126 ай бұрын
I noticed this flaw too. Fortunately, someone had described this problem earlier, so my worries quickly disappeared.
@Blake_475 ай бұрын
11:57 The Potential energy is mglsin theta since the restoring force is mg sine theta
@sickboi111113 жыл бұрын
This video deserves to be prefaced with links to the sources for related and assumed knowledge, so people can get the pre-requisite knowledge required to understand and appreciate this video.
@alivia1812 жыл бұрын
Thank you so much Sir for this wonderful video. I am starting this topic in my 1st year. It is very helpful .
@yansayidiyegrace8542 жыл бұрын
Are You Physics Student at University? I recommend this: kzbin.info/www/bejne/noi3YWlvr85qo68
@quantummechanic88972 жыл бұрын
The best playlist kzbin.info/www/bejne/noi3YWlvr85qo68&ab_channel=BiPhysiMath-Special
@yiwang253711 ай бұрын
I just realized how important is this when I saw the "LAGRANGIAN" is so big. !
@tutrinhngoc43892 жыл бұрын
Thank you so much 😘 From vietnam with love
@navneet15333 жыл бұрын
Mr physics explained make more video on Lagrangian principle it's so helpful for me👍🏻
@HaliPuppehАй бұрын
T was chosen by the person who introduced the concept of kinetic energy. It stands for "translational" cause it's the energy of movement
@1973jdmc2 жыл бұрын
Exceptional introduction- THANK YOU
@quantummechanic88972 жыл бұрын
The best playlist kzbin.info/www/bejne/noi3YWlvr85qo68&ab_channel=BiPhysiMath-Special
@lloydbotway59302 жыл бұрын
Excellent straightforward explanation
@quantummechanic88972 жыл бұрын
The best playlist kzbin.info/www/bejne/noi3YWlvr85qo68&ab_channel=BiPhysiMath-Special
@martinullrich6558 ай бұрын
Thanks for the super tutorial! (Last formular of the pendulum: instead of "L" should be "l" [length of pendulum])
@igorbarros33083 жыл бұрын
simple and easy to understand, thank you!!!!
@richardrigling49063 жыл бұрын
At time stamp 10:30, shouldn't it be mg = -my dot?
@youtubeuser10523 жыл бұрын
It's been a long time since I studied multi variable calculus. Can you remind me why you can assume ydot doesn't depend on y? When taking the partial of ydot with respect to y my first thought is that ydot could possibly be equal to a function of y so I wouldn't assume the ydot term would be zero.
@bingusiswatching63352 жыл бұрын
I'm new to this but I think its more to do with the lagrangian itself, to predict an objects motion it requires an initial velocity and position which are not dependent on each other in configuration space?
@user-lb1ib8rz4h2 жыл бұрын
they're taking the partial of L wrt y, and L is a function y, ydot, and t. so we ignore the ydot and t if taking the partial wrt y
@kristofferh2312 Жыл бұрын
I can see this is a BIG DEAL!
@silverlining68243 жыл бұрын
Mewton: force LaGrange: energy
@TschumiQu27 күн бұрын
aha at 10:38 it's y''=-g not y''=g, since we defined the ground to be 0 and the sky to be positive.
@discreet_boson3 жыл бұрын
Came here from the subreddit Awesome video, liked and subscribed
@Lucky102793 жыл бұрын
This video was really helpful!
@beoptimistic58533 жыл бұрын
kzbin.info/www/bejne/joGmmHqKbqefqLM 👍💐
@jujhaarsingh78893 жыл бұрын
Good video and great explanation.
@beoptimistic58533 жыл бұрын
kzbin.info/www/bejne/joGmmHqKbqefqLM 👍💐
@dybydx31 Жыл бұрын
Great content
@sivavenkateshr3 жыл бұрын
Extremely wonderful video 👏.
@nicolassanchez72593 жыл бұрын
This is great! Thank you! Does someone learn this as an engineer? Because I study Civil but have never seen this.
@DotPhysics3 жыл бұрын
For civil engineering - you might not get to this stuff.
@diatlemaboe99423 жыл бұрын
Mechanical engineering - vibration, yeah
@nicolassanchez72593 жыл бұрын
@@diatlemaboe9942 yess I'm taking a class in vibrations and you see this stuff
@definty3 жыл бұрын
I like the introduction series
@beoptimistic58533 жыл бұрын
kzbin.info/www/bejne/joGmmHqKbqefqLM 👍💐
@amudonchingangbam92562 жыл бұрын
That 'identical' caught me off guard.. 🤣🤣🤣
@yansayidiyegrace8542 жыл бұрын
Are You Physics Student at University? I recommend this: kzbin.info/www/bejne/noi3YWlvr85qo68
@quantummechanic88972 жыл бұрын
The best playlist kzbin.info/www/bejne/noi3YWlvr85qo68&ab_channel=BiPhysiMath-Special
@usman6323 Жыл бұрын
Amazing intro to lagrangian.
@DotPhysics Жыл бұрын
thanks!
@raunacsen1792 жыл бұрын
Thank u sir for this nice explanation 👍🏻👏🙏
@allekshaАй бұрын
Many thanks! There is an obvious mistake at 10:25 . You've lost te sign. There y double dots should be equal to minus g
@clarysshowАй бұрын
Afte practising so many questions, I have seen making mistakes due to writing x prime or x dot to show the velocity in x direction and it's not so efficient to always write like those old books, I do not make mistakes in differentiation or calculus, I make mistakes in distinguishing between velocity and coordinate. So I start writing Vx or Vy or Vz or Vi to show velocity XD
@melchiortod293 жыл бұрын
T stands for travaille i think. Which means work
@Khutso127910 ай бұрын
Wow, u made it easier
@mrtienphysics6667 ай бұрын
The Langrangian is the excess of kinetic energy over the potential energy of a system. ref: Lanczos
@harshpandey7970 Жыл бұрын
So simply explained thanks ❤️
@DotPhysics Жыл бұрын
Glad it was helpful!
@TimurChepiga3 жыл бұрын
@ 10:36 its negative g. great video!
@tps84702 жыл бұрын
Nice Explanation
@yansayidiyegrace8542 жыл бұрын
Are You Physics Student at University? I recommend this: kzbin.info/www/bejne/noi3YWlvr85qo68
@quantummechanic88972 жыл бұрын
The best playlist kzbin.info/www/bejne/noi3YWlvr85qo68&ab_channel=BiPhysiMath-Special
@Imran52Feb2 жыл бұрын
Will it not be Theta double dot =- g sin Theta/ Lower case L rather than capital L in the denominator? Also del L/ Del theta dot is zero in the first term because Theta dot is a function of time and not Theta. Am I right?
@seungjungjin92177 ай бұрын
thanks for a great video!
@DotPhysics7 ай бұрын
Glad you liked it!
@djttv Жыл бұрын
Very clear explanation of how to do problems using lagrangian dynamics, but I still wonder where it comes from. Why did someone define L=T-U in the first place, etc. Great video!
@DotPhysics Жыл бұрын
I think, like many concepts in physics, we use the Lagrangian just because it works. Lagrange showed that if you defined L, then the action integral would be the same as the actual trajectory. It's crazy.
@miloszforman6270 Жыл бұрын
_"Great video!"_ _"but I still wonder where it comes from"_ Isn't that some kind of contradiction? If you can't understand it from the video, probably it's a bad video. We would not have to bother, but this guy is stealing our time.
@eldarr0uge4822 жыл бұрын
Kinetic energy translates to "énergie cinétique" in french, so the T probably doesn't come from there ^^
@bernicenwabueze924Ай бұрын
Perfect
@ronaldjorgensen68399 ай бұрын
i prefer bance newtons cradle at each instance practice problem sets never tried double pendulum other than upside down newtons cradle at inverse forces
@JoeHynes2842 жыл бұрын
i love this channel
@hayatabbas473210 ай бұрын
Great lecture!! Thanks
@DotPhysics10 ай бұрын
Glad it was helpful!
@dwrd73563 жыл бұрын
This is a really amazing video!. Actually I was a little bit confused in 13:11, why y' is d/dt(lcos(theta))? it shouldn't by d/dt(-lcos(theta))?
@NateRiver-ph9co3 жыл бұрын
I´d like to know as well
@user13rs2583 жыл бұрын
It gets fixed while adding their square if you have noticed it, even if it is fixed by mistake. 😂😂 I mean because of squaring and getting the right answer 😁
@arinahomuleba4165 Жыл бұрын
Thanks a lot, my lecturer sucks at this😫
@DotPhysics Жыл бұрын
I'm happy you found this useful (but not happy your instructor isn't useful). Here's my current course in classical mechanics (but we aren't yet to the Lagrangian). kzbin.info/aero/PLWFlMBumSLSbZvcPMA0nH60x1ebX4XSqB
@dorol63752 жыл бұрын
Ah yes I should clearly be learning this going to 10th grade
@currenredman18643 жыл бұрын
Great video, helped a lot. Also, would you happen to know why we use T-U as the lagrangian? I can't seem to find a good answer anywhere
@gibbogle9 ай бұрын
Same here. I'm guessing that was a lot of development by different mathematicians, maybe spanning years, to arrive at L = T - U. The teachers don't go into the history.
@NicolasSchmidMusic3 жыл бұрын
I don't think the T has a particular meaning in french either...
@AnuragGuptainspired3 жыл бұрын
How will we obtain the Lagragian for an object sliding under the influence of force 'F' on a frictional surface?
@dr.emmettbrown71832 жыл бұрын
12:05 Potential energy is not - mgl cos@ but mgl (1 - cos@)
@mohammadmahirareeb75135 ай бұрын
didnt know cheatcode existed irl💀💀
@anbudamodaran41622 жыл бұрын
Interesting problem at 4:45, looks very familiar...
@ashutoshpurohit86033 жыл бұрын
nicely explained !
@riccardogarzelli14 күн бұрын
Motion of a ball y 2 dots = -g because my2dots + mg = 0
@jackdeago36392 жыл бұрын
Thank you so much
@lanefaulhaber1824Ай бұрын
How does the problem change when you have a pendulum in 3D space? when I plug my z value in, is it also lcos(theta)(theta-dot)? Or would the angle be different when referring to z? And then how does that affect the rest of the process??
@uditamaitra26132 жыл бұрын
Thank you sir
@markostojanovic59303 жыл бұрын
Great video and great explanation!!! I'm becoming a fan.
@piotrprs5723 жыл бұрын
GOOD JOB with this movie... Now I will check with others u movies. Maybe this channel is worth to recommend to others. :-)
@beoptimistic58533 жыл бұрын
kzbin.info/www/bejne/joGmmHqKbqefqLM 👍💐
@andrejburcev60232 жыл бұрын
At 10:28 acceleration should be -g
@user-pb4jg2dh4w3 жыл бұрын
Aahh yeah this man needs more than just one like
@arnabc Жыл бұрын
Not sure about the right hand plot at 5:39. S, as defined by the integral, is a just a constant for each path, since y is a function of t, and we are integrating wrt t. So any plot S should be against "path". How is that represented by the horizontal axis?
@miloszforman6270 Жыл бұрын
Sorry to say that, but it's an awkward BS diagram as well as an awkward BS explanation. Thumbs down.
@karanaimaАй бұрын
Amazing
@CypherSpectre3 жыл бұрын
Travail = Work
@arnabc Жыл бұрын
You missed a minus at 10:23. As a result you got y''=g, which is obviously wrong, as the acceln due to gravity is DOWNWARDS!
@Stuk4s3 жыл бұрын
Awesome video 😍
@DotPhysics3 жыл бұрын
Thanks 🤗
@classictutor3 жыл бұрын
Could you explain why L is defined as T - U? Also when you were doing the partials around @10:00, even though y dot and y are different variables, isn't y dot still dependent on y and vice versa? So if you are doing the partial of one variable, wouldn't the other be affected as well, in other words when you are doing the partial of y the y dot is moving and vice versa so that the results are not clean? Help me if I am over thinking or there is something to this.
@maalikserebryakov2 жыл бұрын
Thats like asking why is newtonian Force defined as the product of mass and acceleration. These are just definitions invented to make calculation possible. you can invent a new definition yourself but the difficult part is to come up with a definition that is useful in calculation
@classictutor2 жыл бұрын
@@maalikserebryakov Useful for calculation is good enough for me. I thought there was something more deeper.
@maalikserebryakov2 жыл бұрын
@@classictutor yes thats all there is to it nothing deeper at all 👍
@MrSidney9 Жыл бұрын
@@maalikserebryakov Net force being equal mass times acceleration is not “a definition invented “ it’s a fact about the natural world transcribed in mathematical term. L=T-U is however purely definitional, and useless considered by itself; However, the Lagrangian EQUATION, is a statement about the physical world.
@SolidSiren Жыл бұрын
Wym there is no tension equation? T = mv^2/r + mgcosx
@himanshuramoliya92213 жыл бұрын
Very good explanation !!
@thomasalgado15 Жыл бұрын
Should that derivative with respect y be my' * mdy'/dy - mg?
@RoboMarchello Жыл бұрын
thanks!
@DotPhysics Жыл бұрын
No problem!
@alejandro546833 жыл бұрын
AMAZING ! , SUSCRIBED INMEDIATLY
@281992pdr8 ай бұрын
There ARE two forces not there is two forces. Conceptual clarity depends on prcision of expression.
@mihadbinislamtanim62673 жыл бұрын
at 11:58 shouldn't the potential energy be U = mg(l - lcos(theta))
@st_s3lios8603 жыл бұрын
It's actually the same. You just put the origine of potentiel to the bottom when he put it to the top. But whatever, the constant will diseapper when you will derive (sorry for my bad english)
@atheroot2 жыл бұрын
@@st_s3lios860 no, it's not the same. Looks like the author don't understand the topic.
@djvnsdjkvnsfjsrhbgdh3 жыл бұрын
Great Videos keep it up!
@speedbiker61322 жыл бұрын
that path from 4:47 is something familiar !?
@hu511610 ай бұрын
Great vid!
@brighttech3470 Жыл бұрын
i have some doubt why we take the derivitive of the lagrangian function for the solutions ? and how does it work ?
@fpgaguy2 жыл бұрын
I think something is wrong with me; I keep watching this type of stuff for fun :-)
@pritamroy37668 ай бұрын
Hi, Dot physics I have two question and im seeking my answer for long time never satisfied with any.1) why lagrangian are defined like L=T-U??? Why not any otjer form like L= sin T- log U or amy othe rkind of weired combination??? Dpes lagrange derrive this perticuler form from Anywhere or he got it in his dream??? 2) if a system is in motion with non conservative force, only like friction can we still define Lagrangian??? How???
@grahamashton721028 күн бұрын
The Lagrangian takes different forms depending upon the theory in question - and yes he dreamt it in just the way Newton dreamt F=ma. It's a guess that can be compared with reality.
@arahman38973 жыл бұрын
Thank u sir.
@soundarrajankannan76922 жыл бұрын
excellent teaching sir. But just one doubt, in potential energy, for Y we have to substitute (l - l cos(theta)) right??
@BederikStorm9 ай бұрын
It must be -g, not +g for the second derivative of y.