5:05 AM
1

I'm reading Simmons's Differential Equations and find that I have to obtain Euler-Lagrange equations of the following integrand (integrand of the action functional): $L = \frac 1 2 m \Big\lbrace \Big(\frac{dx}{dt}\Big)^2+\Big(\frac{dy}{dt}^2\Big)+\Big(\frac{dz}{dt}\Big)^2 \Big\rbrace - V(x,y,z)$...

This article discusses the history of the principle of least action. For the application, please refer to action (physics). The principle of least action – or, more accurately, the principle of stationary action – is a variational principle that, when applied to the action of a mechanical system, can be used to obtain the equations of motion for that system. In relativity, a different action must be minimized or maximized. The principle can be used to derive Newtonian, Lagrangian and Hamiltonian equations of motion, and even general relativity (see Einstein–Hilbert action). The physicist Paul Dirac...

6 hours later…
10:57 AM
@amWhy: Do we really need an April Fools' tag on meta? — Asaf Karagila 1 hour ago
@AsafKaragila Maybe this could be a separate discussion, possibly in tagging chat room. As I have already mentioned there, the tag with the same name exists on Meta Stack Exchange. (And it is quite likely that we could get a bunch of questions where such tag could be suitable roughly at this time of the year.) — Martin Sleziak 29 secs ago
On meta.SE there is tag: meta.stackexchange.com/questions/tagged/april-fools They have even created - I'd say the latter would probably be too specific for our meta, but personally I'm ok with the former.
@Martin: True. But with maaaybe one question a year, the tag will fall into misuse and get deleted every year anew. So... what's the point? :) — Asaf Karagila 1 min ago
Some past questions about April Fools' topic:
5

What is this game that appear in all pages of MSE from yesterday?! It happens only for me or it happens for all users?

36

The bot is here to fool people as 01 Apr is April Fool's Day. I chatted with the machine just now myself for about 5 min. This is just part of SE's way of having some fun with its users. Everyone, enjoy!

4

The question is in the title. What do the Unicoins do for us? Why are they on MSE? What is this mining business about?

This year there was also this question: Why does Quack Overflow start listening although I explicitly tell it I don't have a microphone? But the OP decided to delete it after being told in comments that this was already answered on Meta StackExchange.
@AsafKaragila I do not have strong feelings either way - whether the tag should stay or should be removed. In any case, to address your objections.
One of them was that the tag gets automatically removed until next year - since there is only one occurrence. I have added tag-excerpt and tag-wiki, so this is no longer an issue.
The other one is that the tag is likely to get misused. I am not sure, it's certainly possible. But probably from this viewpoint it is not worse than the already existing tag.
BTW the "What's the point" comment reminded me of MathOverflow.
in MathOverflow, Dec 3 '17 at 3:16, by Martin Sleziak
"it's not worth it", "let it all go down the drain", "not moving a finger any more"
in MathOverflow, Dec 3 '17 at 3:16, by Martin Sleziak
Reading some comments from MO users, one might get impression that they have rather pessimistic approach to the site. :-)

12:12 PM
The tag was edited away.
@AsafKaragila Not at all. It was only my mini April Fools contribution. — amWhy 8 mins ago

2 hours later…
2:20 PM
Am I the only one to think that the does not make much sense?
0

Can the distribution of $X+Y$ be equal to the convolution of the distributions of $X$ and $Y$ when the random variables are not independent? In particular can this be true when $X=Y$?. This leads to $$(F\ast F)(x)=F(\frac x2) \forall x ...(1)$$ One example of such a distribution is the Cauchy di...

BTW grew to 89 questions.
Maybe it's the time to raise this on meta? Even if the tags stays, it should probably be at least discussed whether it is useful or not.