The h Bar

@Skyler You're evil and twisted

@Skyler that does sound satisfying.

I have days/afternoons where I go work through some physics thing.

@ACuriousMind well I mean a really nice roadmap

it could be a bit masochistic but I think compared to all the other subject EM really is the best for learning like this

I think statistical mechanics is similar.

6:26 PM

@DanielSank you really pull a lot more out of your hat in stat mech though, in EM EVERYTHING is basically Maxwell's Equations

@Skyler Oh, I dunno.

@DanielSank remember in stat mech how many times you taylor expand and things just work

Stat mech is kinda special in that there are essentially zero physical laws involved at the ground level.

It's really just counting.

@DanielSank very true, one of the reasons I really like it

hmm, gtg. @Skyler can you respond to my email about Smashing tomorrow so Jason can see that it's actually happening?

6:29 PM

@DanielSank thanks, hadnt checked emails since waking up

just replied

6:40 PM

@BernardMeurer you have to admit you'd probably really learn it well, and that learning EM in that detail would probably be more useful than learning the other disciplines with such rigor

@Skyler Indeed, that is true

I have classical mech next semester

not sure how much I'm looking forward to it

@Skyler What do you classify as EM here, classical stuff?

@alarge lets leave self-interactions out of it

i dont know how quantized EM works so lets do classical (for now)

@Skyler What's there to learn then that carries over to other areas? I mean sure, if you go a la Jackson, you will have learned a lot about PDE solution methodologies.

@alarge experimental stuff more, antenna design, mix with learning digital systems and you can do communication.

i mean if you do mechanics but remove the stiff material approximations that can carry over into a bunch of experimental stuff too but thats pretty nightmarish

6:51 PM

Well I guess the same arguments could be made for almost all the other disciplines though, like continuum mechanics, fluid dynamics, thermodynamics

@alarge forgot about fluids, good point

thermo I really like (stat mech at least) but its got a lot more of those magical moments where you take a leap of faith and things work

or at least them not working is reduced to less than 10^-23

And you could argue QM from semiconductor POV if applicability is what you're after

Q: chosen answers with many negative votes

@alarge eh semiconductor is more statmech with a dash of quantum

you really just use quantization from QM, maybe bloch potentials or perturbation theory if youre really being rigorous

right?

Physics Meta

0

I am bothered by chosen by OP questions which are evidently wrong within standard peer reviewed physics , this is an example Since one of the aims of the site is to be searchable and be a basis for physics questions on the net, the set up of a chosen by OP answer with negative votes seems a mock...

discussion

7:11 PM

@BernardMeurer You need that.

You will learn about Lagrange and Hamilton.

These are amazing things.

I know I need it, I'm just lazy :P

@BernardMeurer, I will tantalize you so that you look forward to it.

The following is true:

Like you did with linear algebra?

Consider a physical quantity called "action", which is defined as $S \equiv \int \mathcal{L}(t) \, dt$.

Here $\mathcal{L}$ is a thing called the "Lagrangian" of the system, and it is usually the kinetic energy minus the potential energy.

It is true that physical systems always move such that $S$ is minimized.

Okay, I believe you so far

7:14 PM

You can describe everything from flying baseballs, to systems of pulleys, to quantum fields using that framework.

It is the master framework of the universe.

You'll learn about this in mechanics.

When I want to work out the dynamics of quantum circuits, I start with the Lagrangian. It's the only guaranteed way to not screw up.

Wat

Really?

Yep.

There's more. Check this out.

But wait, there's more!

Suppose I give you some complicated mechanical system where various parts are connected to other various parts by rods, ropes, whatever.

Problems like this are very, very difficult because there are constraints.

See, Newton figured out $F = ma$, and that is true, but its only easy to apply that low if you know $F$.

If I put an object on a table, the force upward from the table depends on how hard I push down on the object.

The constraint is "object can't fall through table", and the force from the table reacts to make that true.

See? In cases like that, $F=ma$ is impractical because $F$ isn't set.

Do you see what I mean?

I do, yeah

Makes sense

7:19 PM

Ok, so Lagrange comes and saves your @$$.

See, the rule I said, that $S$ is minimized, works even when $\mathcal{L}$ is written in terms of constrained coordinates.

ass isn't a curse word dude

and everyone can read you wrote ass there

So, suppose I have a bead on a wire. The only "coordinate" of the system is the distance of the bead along the wire.

The wire could be curvy... any shape.

We know that the wire is pushing on the bead in weird ways to enforce that constraint.

Alright

But Lagrange doesn't care. You make up $x\equiv \text{position of bead along wire}$ and write $\mathcal{L}$ in terms of $x$, and the framework still works.

What? How?

7:21 PM

You can completely forget about the force of the wire holding the bead on the wire and still solve for the motion of the bead.

How can it always work?

@BernardMeurer F------ magic.

This is some samurai shit

@BernardMeurer Yes, it is absolutely incredible.

It makes all kinds of mechanics problems that would be incredibly difficult really easy.

What the fuck is this

7:22 PM

So for example, suppose I make a bead on a curvy wire that goes from some high position to a low position... kind of like a roller coaster.

And I want to know the position of the bead on the wire versus time.

Alright

All I have to do is write the potential and kinetic energy in terms of where the bead is on the wire and Lagrange spits out the equations of motion.

(They may not be easy to solve, but at least you get the equations and can solve on computer)

That's some next level crap

Now here's the really cool part.

But how does it account for the shape of the wire?

7:24 PM

Suppose you actually do want to know the force on the wire, because for example, you're an engineer and you want to make sure your roller coaster doesn't collapse.

Lagrange can tell you that too.

I gotta go cool down my cryo.

Talk later.

Did you ever drop that cube I gave you in the cryo?

I still want to know what happens :P

I'm liking this lagrange guy

Q: What is the work done by internal forces of human body while sliding down a rough inclined plane?

@DanielSank hey, actually theres a paper i was really interested in that I tossed here in chat back when you were asking about something about lagrangians

did you ever see it

GPhys

7:47 PM

@vzn Computational Physics is one of the required first-year PhD courses here

It's actually been kind of fun

I mean, sure I knew how to do Euler's method and a finite difference before the class

But neither of those are really practical

user246160

Could anyone here try to answer this one ? physics.stackexchange.com/questions/297906/…

user246160

0

How is the work done by internal forces of a human body calculated when a person slides down a rough incline calculated ? According to one of my textbooks it is just numerically equal to the change in potential energy of the body. But I feel that the body also has to do some work against fri...

homework-and-exercises newtonian-mechanics friction work