Physics 70 Principle of Least Action (1 of 27) What is the Principle of Least Action?

We will learn The Principle of Least Action is when a particle moving under the influence of a force (like a gravitational force) will take a path in such a manner that the time averaged kinetic energy of the particle minus the averaged potential energy of the particle is a minimum.

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[theultimatereductionist]

"Principle of Least Action" YES! THANK you for covering this topic!

[Titurel]

Thank you for doing this! One of the best explanations available on video.

[kaursingh]

u r the best on this topic -- u r best on every topic - my concept cleared - thank u sir

[aqeelshah]

Wow this professor is so genius. You are miracle man i think! Anyhow Thank you so much

[SumitYadav-mxbp]

You made it so simple that, even any high school student would understand least action principle, thank you for making this so simple, . ;)

[aajeev]

Wow. Professor. This will be an amazing series! Can’t wait to watch them all.

[ptyptypty]

can't wait to see ALL these videos!! Thanks Michel.... I'm going to guess that the parabolic path of a projectile in a gravitational field IS THE PATH OF LEAST ACTION!!.. lol... No other Graph will provide the least action.... But I'll have to wait to see all your videos to know if that was a reasonable guess.. :D ...

[rajeshramalingam]

sir, here you are noting that the variation between two fixed points ( A and B) and two fixed time ( t1 and t2 ), but this del variation is used for 'Hamilton's principle' in the text. In the same text, Another del variation ( inverted triangle ) is used for 'principle of least action', where time is varied for each paths. Clarify this pls...

[andrewtaylor]

The definition is completely clear, and the math that follows is too. But what is the physical intuition that gave anyone the idea of the Principle of Least Action? Surely it was more than just a guess. Why would a particle take the path that minimizes the integrated average of the KE-PE? There must of been some intuition for why Lagrange wrote this down. I can't find any explanation of this.

[sigietharyopranoto]

Sir, is the principle of least action same as the calculus of variations ?
Thank you

[kaursingh]

please explain poisson bracket ; hamiltonian ; hamiltonian jacobi --thank u sir

[nraynaud]

weird, it seems that your website is down, it resolves but times out on http. It pings ok (156 ms from France)

[larrybryant]

I would guess that all energy approaches equilibrium and the lowest state. It is not clear why we are using this energy difference over the sum of these terms.

[ugursoydan]

PROFESSOR, BUT WHY AN OBJECT MINIMIZES THE DIFFERENCE BETWEEN KINETIC AND POTENTIAL ENERGIES? WHAT IS THE REASON OF IT? PLEASE TELL ME. THANK YOU

[SkanderTALEBHACINE]

thanks, just a question, you said average KE - average PE but you wrote on every part (KE-PE)*delta(t), how's that? please more explication and thanks again

[drbonesshow]

The Principle of Most Action is moshing your way around a nightclub or stadium.

[paulsutton]

Why MINUS? Nobody ever explains why the action is MINUS?