Lagrangian and Hamiltonian Mechanics in Under 20 Minutes: Physics Mini Lesson
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- เผยแพร่เมื่อ 13 ก.ย. 2021
- There's a lot more to physics than F = ma! In this physics mini lesson, I'll introduce you to the Lagrangian and Hamiltonian formulations of mechanics. Get the notes for free here: courses.physicswithelliot.com...
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When you take your first physics class, you learn all about F = ma---i.e. Isaac Newton's approach to classical mechanics. But there's a lot more to mechanics than F = ma, and modern physicists actually more commonly use two other formulations of mechanics: the Lagrangian and Hamiltonian formalisms. In this video, I'll teach you the basics of both. They're not only powerful approaches to classical mechanics, they're also fundamental to the way we think about quantum mechanics!
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- All About Pendulums: • Everything You Need To...
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About physics mini lessons:
In these intermediate-level physics lessons, I'll try to give you a self-contained introduction to some fascinating physics topics. If you're just getting started on your physics journey, you might not understand every single detail in every video---that's totally fine! What I'm really hoping is that you'll be inspired to go off and keep learning more on your own.
About me:
I’m Dr. Elliot Schneider. I love physics, and I want to help others learn (and learn to love) physics, too. Whether you’re a beginner just starting out with your physics studies, a more advanced student, or a lifelong learner, I hope you’ll find resources here that enable you to deepen your understanding of the laws of nature. For more cool physics stuff, visit me at www.physicswithelliot.com. - วิทยาศาสตร์และเทคโนโลยี
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If the Lagrangian and Hamiltonian formulations look pretty similar, to the point of almost being different notations, this is because Hamilton invented the term "Lagrangian" and codified Lagrangian mechanics as we know it, and it was Hamilton's obsession with notation that led him to make the equations look as symmetrical as possible with the P's and Q's, which paid off 100 years later with quantum mechanics
So basically autism good
I independently learned or realized that Einsteinian physics is diverted from Newtonian, and Newtonian can be seen in relation to the physics of Gottfried Wilhelm Leibniz (Leibnizian physics?) due to the calculus controversy both men had. Leibniz' material as a variety of Newtons from an "english mind view" whilst germans would have Leibniz as a physics "block" in a "german mind view" or mindset . So am i putting some spot on an alternative genus of physics view, on another branch in some way?
Newton-Leibnizian, Lagrangian-Hamiltonian and Einsteinian physics a the three types or groups (so far?)?
@@Simon_Jakle__almost_real_name I'm familiar with Leibniz as a great mathematician and philosopher, though I don't know his involvement in the development of mechanics, I will read to learn more about that. Certainly Hamilton and Lagrange built on the work of Euler and the Bernoulli's as well as Newton, so I agree that the development of mechanics was a fully cross-national effort.
@@iyziejane I guess i am not a very integer physics mind, because the world of knowledge (and ist effects possibilities) is so vast and the changes beneath humanity happen to swift and kinda-feel absorbing too often, but i went through some rather german based physics history and my recocnition would be:
Distinguishing physics i would see a seven level pyramid,
beginning in the antique
then around the 16th century Kopernikus, Galilei and Kepler
to be followed by the Lagrangian-Hamiltonian physics
with Kelvin and Maxwell as a next level
until physics put foot with Einsteinian-Planck-ian physics (with some Conrad Röntgen)
plus some ingenious Material from/by Niels Bohr, Enrico Fermi, John Wheeler and Hawking.
And then entanglement with chemistry.
Until the mostly too demanding algorithm of Peter Shor.
But as often i cant intensivate such a list if i would try to explain the view in my mind, i rather try to spot and count "the genuses of trees" in/near the world of minds (now and then).
Furthermore, Carl Friedrich Gauß (Gauss) must have been an astonishing person, not just/only about physics.
@@Simon_Jakle__almost_real_name sophisticated Englishmen be like
Future topic suggestion. Noether's theorem. Symmetry. Why is this so important for physics and math?
Thinking of doing Noether next!
@@PhysicswithElliot you could say it’s the topic for, a-Noether video
@@thesuperkat943 *clap clap clap*
@@thesuperkat943 bruh
Yes!!
I wish I had learned this before quantum mechanics. We essentially had a half semester course racing from "what is an operator" through "what's a Hilbert space" to "this is the Schrödinger equation, good luck!". It hasn't even occurred to me to try using Hamiltonian mechanics in classical physics.
QM be like:
Wave functions live in Hilbert space. What is a wave function? IDK
This is Schrödinger eq., solve it
More TISE in 1D square well and SHO
There exist some operators...collapse of wave function
"Bra" and "ket", I can't "c"
Some random n, l, and m stuff
Here is spin, which is a kind of angular momentum, except it has nothing to do with movement
Every word professor said makes sense, but after a lecture everyone is more confused than ever
Prof: think QM is bad? Get ready for E&M!
Me: deliberately looking for a way to switch major despite being almost done with undergrad
Also me: dead inside😭
@@reckerlang2163 @Recker Lang These concepts aren't really as tough as it seems. If you're familiar with classical physics, specially electromagnetism, you can assimilate them very easily with good texts. Quantum Mechanics by mcintyre made QM concepts natural to me, showing the cradle experiments and how they led to the current understanding of those phenomena.
@@celsogoncalves7348 Haha thanks for the advice. I found Griffith’s “Intro to QM” kinda good too tbh. I am definitely not quitting now cuz I really like physics. Cheers my fellow physicists 🥂
We were taught Hamiltonian Mechanics in Classical Mechanics to lead us into QM and Schrodingers Equation more than its use in CM. Schrodingers Equation seemed natural this way.
@@themongoman Very valid point! Even with Griffith, we see a lotta stuff where we have to skip due to “lack of knowledge of mathematical methods”, thus no actual “solving” the problem. Seeing QM in undergrad is both exciting and terrifying b/c like you said we are not ready to see this kinda stuff even after taking modern physics, ordinary Diff. Eq, and linear algebra.
Math is everything in QM, and I remember there was once a friend of mine who is working toward his master degree in theoretical physics tried to explain me outer product and spin using group theory, yet I know nothing about it :( (my math major roommate just learned group theory this year lol) I suppose this is also why there is only 1-2 “real” QM course in undergrad. Thank you for your advices! Physics 4 Life!
(OMG I have never received reply this long on TH-cam, thank you so so much for typing all this up to help a physics newbie out, much appreciated!)
1:49 Newtonian formulation
5:44 Lagrangian formulation (L = K - U)
10:59 Hamiltonian formulation (H = K + U)
I would say:
Newtonian formulation (Σf=mä)
Lagrangian formulation (L = K - U)
Hamiltonian formulation (H = K + U)
@@ronissilva9570ä would snap! i think ur thinking of ẍ lol
@@aug3842exactly
Thank you
As a Physics Freshman, I recall reading the terms "Lagrangian and Hamiltonian Mechanics" in the course description for the Upper Division Classical Mechanics couse and thinking "What does that even mean?".
I figured that I'll learn that when I get there. I got there about 40 years ago!
Inspires me as an undergrad
@@silverspin Stick with it!
Learn how to draw pictures and visualize all of the crazy Physics Stuff; it's essential for building intuition.
Be open-minded about finding your knack: you may find that you have an affinity and talent for something you haven't even tried yet.
What a clear summary, with well thought out supporting materials. You cut to the essence but leave pointers for people to find the details. Great work!
Thank you!
Can it be denied that this guy solves the most difficult problems? th-cam.com/video/pkw92_Jpv1E/w-d-xo.html
the Lagrangian was the most beautiful thing when meeting it in the early courses of studying physics. the way you can just throw away all the complicated geometric/vektor assesments you have in newtons method and just use the energies is so efficient
This really blew my mind, and once again I'm so glad that educational material exists on TH-cam. Thank you for spreading your knowledge; it was mechanawesome! 👍
As a physics teacher I can safely say this is amazing! Succinct and encouraging for a student. Well Done.
Thanks Tom!
I went to graduate school for engineering and that was the best explanation of the Lagrangian/Hamiltonian I have ever listened to.
Very well done! Brilliantly conceived and the use of a consistent scenario makes for a really instructive study.
Me thinks this is going to be a great TH-cam channel!
damn didn't expect you of all youtubers to comment on a video like this!
@@alvarol.martinez5230 Amanda Chaudary from Cat Synth Tv did a video on "square root of pi" for pie day. Multi-dimensional people have multi-dimensional interests.
lagrangian and hamilton are just talking about energy wich comes from newton phisics, no big deal
It's "methinks," one word.
@@LSC69 Noted. And that's why I'm not the Schneider with the PhD 😆
An amazing mini-lecture!
Absolutely awesome. I finally found somewhere that got past the H=KE+PE of Hamiltonian mechanics AND actually explained the point. Thank you.
Glad it helped!
Thanks for this. I've worked with a considerable amount of lagrangians and hamiltonians in my macroeconomics class to determine optimal paths of investment or consumption. It's always interesting to see where our mathematical tools come from.
Glad you liked it Orlando!
And it’s great to see where our 401ks go.
I cannot describe how wonderful this video is. You have encouraged me to learn in my own about a topic I didn't know I liked
these videos hit different and get more appreciation post graduation, forgot what got me into physics in the first place but your videos bring me back in
Really amazing and simplified explanations
Wow, really really wish that this had been available before I studied quantum physics! Thanks for making the vid!
Very best (and simplest) Lagrangian and Hamiltonian explanation
this is incredibly good content. thanks for making it
5:36 that point that you mentioned is such a key to start loving physics if I have to put it I would say love for physics is not a love at first sight it Starts from zero and grows more and more and you can now never hate it.
I've been confused for a whole semester on Lagrangian mechanics and this actually made it very clear, I might actually pass now, thanks!
Nice work! Im a math guy who started studying a little physics after many years; I like it a lot.Greetings from Argentina.
My favourite of these is the Hamiltonian formalism because of its use in Statistical Mechanics and Quantum Mechanics. It really gives a new and very powerful perpective to ask and answer difficult questions about systems we cannot hope to deal with using bare Newtonian Mechanics.
Very clear and well presented. I briefly learned Lagrangian and Hamiltonian formulations 20 years ago in Dynamics and promptly forgot them. Now I'm teaching myself more physics and they keep popping up. Thank you!
Thanks Ted! Glad it was helpful!
Interesting and fascinating. I like the Hamiltonian Flow. Path of least action vs Path of least resistance(electron flow). Just beautiful stuff!
Please keep making more physics videos. This was so helpful.
Thank you Anna!
I wish this had been presented in my grad school classical mechanics course.
Yes, do a few calculations using Lagrange mechanics! That really helps to appreciate it, especially for constrained systems.
A very worthwhile refresher video.
More math in Lagrangian and Hamiltonian Mechanics? Wonderful, I look forward to learning it
Well done. I've heard of these but don't think I learned this in undergrad engineering. I was able to listen to your explanations and understand them, taking your word for it that you were doing the math right. That takes too much patience, and I would never use it in my profession, but if I can just grasp the basic ideas that is really educational and you never know how you might use them.
Great video and explanations. We essentially exclusively use Lagrangian mechanics in microeconomics bc of the simplification of all the moving parts involved
I'm an Econ undergrad and it's nice to see how similar these approaches are to what I saw in an intro to Dynamic Optimization.
The Lagrangian formalism can also be derived from the principle of virtual work, which in itself is already a very strong formalism for classical mechanics. I prefer this approach since it more naturally accounts for non-conservative forces too. Maybe an idea for a future video?
Thank you. Enjoyed your Physics videos. Been a long time since I jumped from Physics to Programming.
Wow. The best video I have seen in the last year! Great explanation. I learned a lot!
Was just thinking the -p²/2m was very reminiscent of shrödinger. Then I watched the end and you were speaking of quantum mechanics using the Hamiltonian. I've been out of physics now for a few years and had forgotten how much I enjoyed doing it. Thank you.
Good stuff. Keep pouring the knowledge.
Finally you have enabled me to understand these three formulations of mechanics that I first learned in graduate school in 1968. I have no need of them now as a retired scientist but thank you!
There are more formulations
@@maalikserebryakov who asked
Wow this mini lessons are very good!! very clear and straightforward presentation
Most helpful 20 minutes that I’ve ever spent on this topic!
Glad it was helpful!
Thank you for making a hard subject more approachable. Great channel!
Thanks Nathan! Glad it helped
phenomenal work
Fantastic explanation!
Regarding the 2 different types of curves in phase-space after 17:00, I presume the internal ones, which touch the horizontal axis (dp/dt = 0) are where the pendulum swings back and forth (momentarily zero velocity when changing directions). The 2 external curves are where the pendulum swings/rotates around the pivot point: one is clockwise rotation and the other is counter-clockwise rotation.
Yep!
This channel will soon reach million subs.
Yes very clear video, you make these concepts very enjoyable to watch and listen to.
Great explanation. Thanks!
Love from India Mr.Elliot❤I am really enjoying your videos...they are very conceptual...you explain so nicely everything..Please make whole playlist of quantum field theory from basics....God bless you🙏
You, my friend, deserve millions of subscribers. Such wonderful content you are delivering here! Thank you! I wish you the best in all you do.
Thank you Vincent!
Remember encountering this almost 50 years ago (TU Berlin) - Theoretical Physics I (I think, you'd use 101). We used to talk of Eulerian observer and Hamiltonian observer. One sitting at the river bank and the other swimming, sort of fun thought experiment using the respective equations.
Amazing stuff! I’m on my way to towards understanding Schrodinger’s famous equation! This is the best compare/contrast between Lagrangian and the Hamiltonian on TH-cam… although it would be cooler if I could see a ‘phase’ space for the Lagrangian… ( would it be the same?).
Amazing, thank you so much. It was music to the ears listening to you!
Thanks for the explanation, it really helped me understand
Instantly subscribed. Great channel!
Thank you so much for saving my semester. I'm doing a second year classical mechanics course and I haven't been understanding most of lagrangian and hamiltonian. But now I do. Excellent tutorials
Glad it helped Amahle!
Y is it that we understand TH-cam tutorials so much better than our classes? Are TH-cam teachers just much much better or is our focus not on our classes or the methodology of teaching in our institutions is bad? And very nice video btw.
Awesome explanation, thank you!
just what i had been searching all day
This so underrated.. please dont stop doing content like this!
Thanks Pedro!
Appreciating your effort. Well done!
Thanks Deepak!
All of a sudden I'm glad I kept this video in my watch later for over a year because coincedentally I took calculus and understand some of it
thank you soooooo much for this simplified yet extremely informative introduction!!!!!! I'm not studying physics but somehow the course uses a lot the terms you mentioned in this video without giving us proper explanation! and i'm too dumb and short on time to start a whole course on physics just to understand these concept. you are such a lifesaver!! 🥰🥰
Glad it was helpful!
Can it be denied that this guy solves the most difficult problems? th-cam.com/video/pkw92_Jpv1E/w-d-xo.html
If only there had been this channel during my university times , I would have been one of the best in my class, excellent explanation , thank you
Thanks!
Yeah but when this video exists so do algorithms whose purpose is to feed you a functionally infinite amount of content that it predicts you will waste your time on, so it balances out.
Thanks a lot for sharing, very didactic indeed. Exactly what I was looking for, to get a quick introduction in the two different approaches!
This was easily one of the best videos I've ever watched. Subbed
Thank you!
@@PhysicswithElliot My pleasure. Literally 😃
Thx for the nice video! Tip: when you introduce something new (like Lagrangian and Hamiltonian mechanics), then produce a SIMPLE problem for viewers to try to solve on their own, and only after that a more complex problem
I’m just here to support you and I don’t know anything about physics but I will watch to support and learn about it
Thank you very much dear eliot.3 in 1 shot.
Thanks...🙏 This helpful for my study..
im a 12th grade student this was quite fascinating to me as physics has always been fascinating
I would like to give you some serious credit for your teaching abilities and methods. This is movie is excellent material to study for a teacher, and has great pedagogic value. I'm not trying to shit on teachers. I have the education to be a high school teacher myself, and I find your movie very inspiring and that it shows me new way to view physics. Bravo!
Thank you very much ! This video explain in a most clear way .
Great video thanks, very clear and engaging
Marvelous. Enlightening.
really well explained
Those little backwards 6 symbols (stylized lower case d) are called partial differentials (or derivatives), they tell you the rate of change of the coordinate in the numerator as the coordinate in the denominator changes. Let's look at a real world example.
You are standing on an uneven stretch of ground with a hill in front of you. Let's call the east-west direction X, and the north-south direction, Y. You want to calculate the change in elevation (height) when you walk from one point to another on the hill. Let's say the point is some distance in the X direction and some distance in the Y direction away from you. We'll use Z for the elevation. So, we are asking for the change in elevation, dZ.
Here's the plan. You will walk in the X direction first and calculate the change in elevation, then turn and walk in the Y direction finding that change in elevation. Adding them together gives you the total change in elevation, dZ. To keep this simple. let's assume the changes are smooth continuous upward changes, in other words, you are always walking uphill.
Let's say the hill has a slope so that the elevation changes at a rate of 20 cm per meter as you walk in the X direction. That is what the partial derivative gives you. It is the change in elevation in the X direction ignoring changes in the Y direction. Let's say you walk 10 meters. Your change will be the rate of change, the partial differential, times the distance you walked, dX. 20 cm/meter x 10 meters = 200 cm.
Now you turn and walk in the Y direction. Let's say the elevation changes at the rate of 5 cm per meter in the Y direction. Let's say you have to walk 20 meters in the Y direction to reach your final destination. Just like before, you multiply the rate of change of the elevation, the partial derivative, times the distance you walked, dY. 5 cm/meter x 20 meters = 100 cm. Remember that you are already 200 cm higher because of the first part of the walk.
Your total change in elevation for the walk is the 200 cm change from the walk in the X direction plus the 100 cm change from the walk in the Y direction. dZ = 200 cm + 100 cm = 300 cm.
That is all partial differentials do, they break down paths into small independent pieces that are then added together to get the total.
Now to keep everything honest. in real world applications all those changes would be very small, and dZ would be the change of your elevation as you walk from one point to the next. I used large numbers to help clarify the process with understandable quantities that we can all relate to.
When we break a vector (a path in some direction) into pieces like this, the pieces are called components.
Of course, this can be extended to any number of coordinates.
Wayne Y. Adams
B.S. Chemistry (ACS Certified)
M.S. Physics
R&D Chemist (9 yrs.)
Physics Instructor (33 yrs., retired)
Thank you sir for wonderful channel to learn physics!
A vivid memory is when my lecturer switched from fixed ("newtonian" Elliot calls it though everything he talked about is actually newtonian) to generalized coordinates like Lagrangian. I later went back to earlier chapters in my trextbook and found it much easier to solve some of the problems there with the new lagrangians. I'm an EE but won't forget the excitement that that revelation brought.
Can you recall which mechanical problem would be the easiest or most basic problem which the Lagrange methods solve better than the usual?
The Lagrangians and hamiltonian formulations were made after newton died and hence are not newtonian. Read the names. 🤡
Good job! Thanks.
Nice Explanation
This is amazing!
Please do more on Lagrangian and Hamiltonian equations.
Awesome!!!! Spark needed for continuing from Newtonian to Lagrangian and Hamiltonaion.....
The best channel I've seen
What an amazing channel! You’ll blow up some day.
great video, elliot. thank you
how wonderful explanation! thanks very much.
I don't have a headache yet but yes at speed 1.5 it's mind blowing. Thank you for your educational skills
Great teaching!:)
The trouble (for me) is that until Lagrange draws attention to it, "action" is an entirely meaningless quantity.
Unlike "total energy", "action" has no physicality.
We might as readily have called upon Lagrange's inside leg measurement.
You might like my video about the action in relativity (th-cam.com/video/KVk1QNTWBxQ/w-d-xo.html), where the physical meaning becomes much clearer: it's the length of the curve that the particle traces out as it moves through spacetime.
I enjoyed your video. I suggest a video comparison the axioms of classical mechanics, quantum mechanics, special relativity, and general relativity, and perhaps quantum field theory.
That takes a tad more math than this video is pitched at.
Good video. Could you elaborate why we want to use H and L , and in which situations?
Another amazing video. Thanks.
What a great video, i really liked it !
What a channel! Subscribed.
Routhian Mechanics would be a fun follow up video
Excellent explanation 👍
So clear!
This is really good video
😢 I was so confused why Lagrangian and Hamiltonian have been ever studied, now I'm convinced and satisfied 😊😊