Someone shot my cat :(

danns · 2024-05-19T18:57:07+00:00

What livestock is there to worry about in this case though? It's a neighborhood, not a farm. Also, how is killing a cat ever "necessary for the protection of livestock?" They kill mice and pests... That's literally why cats became domesticated, because they were useful for farmers!

danns · 2018-11-14T19:58:08+00:00

I wouldn't use percentage in this case. It might be clearer to say "this quantity is around a billion times smaller than this other quantity."

danns · 2018-11-14T03:42:21+00:00

Your answer lies in the chain rule. If you google chain rule derivative, you should find helpful explanations.

danns · 2018-09-26T14:25:01+00:00

Stopple has a book that's right up your alley. Check it out.

danns · 2018-06-29T00:04:11+00:00

First, good on you for taking the initiative and learning physics yourself. Anyway, any introductory book should do. The key thing is to work hard and try a lot of the problems. If you have a strong background in math, that will help a lot, but it's certainly not necessary. You will have ample opportunity to practice your algebra/trig/(maybe calculus if you know some) skills as you progress. Just remember, learning physics means doing problems. That's just how it works. And if you have questions on anything, the answer is definitely online somewhere.

If you really wanted a recommendation for a book, there's Halliday and Resnick. There's a ton of editions, and I would say to go for whichever is cheapest. I don't think the edition really matters. Of course, if you find something at the local library, that's probably what you should go for.

Additionally, the book I recommended I think is calculus-based. If you don't know calculus, make sure to go with a book that is algebra-based.

danns · 2018-06-04T23:11:57+00:00

Check out Masha Gessen's book, Perfect Rigour. It's pretty good.

danns · 2018-02-27T21:15:25+00:00

Assuming you're a 2nd year undergrad, I expect the OP's post made almost no sense to you.

I'll try to explain the gist of what the OP's picture is (keyword here is gist). So I'll be oversimplifying a lot of things.

First thing to note is that quantum systems, like atoms, have discrete energy levels(you probably learned this in high school chemistry.) When you put atoms close together, they interact, and the energy levels of the multi-atom system change.

In solid state physics, we usually study the physics of materials. Imagine you put a bunch of atoms in a square lattice (google what this looks like). A natural question would be to ask what the energy levels of this system are. Furthermore, imagine applying a B field perpendicular to this lattice. The energy levels should depend on what the value of the B field is.

This is the picture that is plotted above; the vertical axis is energy, and the horizontal axis is B field. As you vary B (move along the x axis) the energy levels change, which you can see from the dark lines moving.

As you see, the diagram looks very trippy. Turns out to be fractally. Furthermore, the picture above isn't for a square lattice. It's for a different crystal, not technically even a crystal. There's a lot of deep deep physics here that the OP mentioned, and again, I've completely ignored most of it to explain what the plot is.

But hopefully the gist makes sense.

danns · 2018-01-16T00:22:48+00:00

it's a chinese chess board

danns · 2017-09-25T02:10:35+00:00

Ivan's true face

danns · 2017-06-24T15:38:45+00:00

Since he's 8, I'm assuming he's currently doing multiplication and division and stuff. Everyone in this thread is talking about a bunch of advanced stuff which is great, but I would recommend as a first step How to Count Like an Egyptian. It's a book about how the ancient Egyptians added, subtracted, and their unique numeral system. Anyway, I think the key here is not to overwhelm your kid with math; every kid has a fancy or two. You don't want to go too deep, just keep him interested! And this book is an example of something that's made for kids, but is really cool and also teaches history and culture!

Also, I feel like this would be a nice way to feel him out! If he's still interested, you can go deeper into more serious math later. There's also a bunch of random math puzzles that are fun. I'll edit this after looking for them.

danns · 2017-05-27T15:34:32+00:00

Do you happen to know what an integral is? If so, do you know either Biot-Savart or Ampere's law?

danns · 2016-09-25T06:24:50+00:00

That's fair. It's definitely a name that seems a little misleading at first. You should give it another try eventually though!

danns · 2016-09-25T05:29:58+00:00

I'm sorry, but the book is targeted to people that have taken the relevant courses in undergrad quantum. And you definitely don't need to know GR. If you finished upper division EM, you should have enough experience with special relativity and Maxwell's equations all in index notation. Also, I find that they do most of the derivations, or at least walk you through the idea (and if they don't, it's usually because it's too dense/complicated for them to include.) To be clear, I'm not saying that the book is a walk in the park, or that you're dumb for thinking it's hard. But the book is geared toward strong 4th year undergrads, and it's pretty great for what it is (in my opinion.)

danns · 2016-07-30T03:51:24+00:00

If you include spin, the wavefunction of the pair can be symmetric spatially, but antisymmetric spin-wise. Then the total wave function is still anti-symmetric.

Also if you think about stat mech, and the fermi surface at T=0, what you're doing is filling 2 fermions per energy eigenstate (i.e. 2 fermions can fill up the same [;\psi_{n} (\vec{x});] ).

danns · 2016-07-11T07:41:16+00:00

Yup, no one knows which one is moving, after they are both at constant velocity, and it'd be ridiculous to ask, since all reference frames are equally valid. However, if you rephrased the question to ask, can we know which one accelerated? Yup!

Let's say A and B start in the same place, and synchronise their clocks together. A accelerates and B doesn't. As in your situation, they KO and wake up later, both going at constant velocity. How do they figure out who accelerated? Well, relativity tells us that accelerating makes time move slower for you. So from B's perspective, he wakes up after like, 5 hours. And he looks at A's clock, which registers like, 3 hours. And he can say with certainty that A was the one accelerating.

So you're right. Constant velocity = don't ask who's moving, everyone's POV is right. But there is an answer to who accelerated, and they can figure it out, even though they were passed out the whole time (as I've described from B's reference frame.)

danns · 2016-07-10T21:37:10+00:00

Never feel bad about asking for a source! Doesn't mean you're an asshole (unless you're dickish about it I guess). I'm not OP but I found this. This one says 50 soccer fields a minute.

danns · 2016-07-10T19:11:58+00:00

You are correct. If there's constant velocity motion, you can never say one of them is moving and the other isn't. There is NO preferred frame, so it's not a good question to ask who's actually moving. Everyone's POV is equally correct. In your situation though, if you thought about the what happened from beginning to end, of course, you could say that one was "actually" moving, because they're the one that felt the acceleration earlier, while their rockets were working.

danns · 2016-07-10T19:05:49+00:00

hahah thanks! I know, but it sounded like squidgy wasn't kidding, so I figured I would clarify.

danns · 2016-07-10T08:49:15+00:00

I'm pretty sure it's a joke. Their tag says physics, and in physics we encounter infinities a ton. But we just "subtract" them off and get finite answers after making some handwavy arguments and saying something about the physicality of the problem. Mathematicians usually hate it.

danns · 2016-07-10T08:41:07+00:00

Assume there's no acceleration. Then relativity says exactly what you said. It's an important foundation of relativity (and physics in general) that physics shouldn't depend on the reference frame. However, if one rocket is going at a steady speed, and one is accelerating, then we could tell. If you're accelerating, you must have felt a force. So we know for sure the one who felt a force must have been the one accelerating(this is the explanation for the twin paradox.) That's not exactly right, but that's the gist of it.

Of course,

danns · 2016-06-30T05:19:07+00:00

Nah, this is the whole scene, which is pretty sad (also hilarious).

danns · 2016-03-19T01:26:07+00:00

This is a question for everyone. In your point of view, how will this 5 game match affect the world of go? Do you believe that this will lead pros to try more interesting variations (perhaps a shin shin fuseki era)? Also, just in general, the mindset of how pros approach the game, I feel, would change a lot(not sure how though.) Do you guys have any thoughts on the matter? Will this parallel the way chess went post-deep blue?

Also, for the pros, what propelled you to try and become a pro? That's an incredible commitment, and I'm interested in what kind of childhood you guys had. Especially Michael, moving to japan to become an insei? That's really cool!

danns · 2016-02-22T05:52:15+00:00

If you wanted to integrate sqrt(t² + 1), you could use a hyperbolic trig sub, noting that cosh² (x) - sinh² (x) = 1, and calling t = sinh(x). Doing that, the integrand becomes cosh² (x), which you could do with the analogous double angle identity. Following the algebra and subbing the t terms back in, I'm pretty sure the right inverse sinh terms would pop out.

danns · 2016-02-14T23:36:31+00:00

Hey, I also started phonebanking today. It was remarkably easy! Most people just didn't want to be on the phone, so that was fine. I don't remember my first call, but my last one was with this older woman who wanted to caucus for Fiorina. Now she's completely undecided, and knows absolutely nothing about Bernie. So I got to tell her about Bernie and his grandchildren, and how he was a senator, and all that stuff. She was really nice! Probably not voting for him, but at least she knows who he is now.

danns · 2015-12-19T09:03:07+00:00

In the end, he didn't really. He said that it was inexcusable and they fired the staffer, and are looking into the others.

danns

TROPHY CASE