/sci/ - Science & Math

>>7656983
I don't even understand what they're trying to say.

They made an inductor with ten windings and an unspecified spacing, using Earth as a core. By what means is an electron forced out the end fast than the speed of causality? Are they implying that the wire can interact with itself via a magnetic field and therefore turn on the light faster than it would take light itself to travel ten times around the earth?

I don't understand why they would frame it that way, but be so ambiguous at the same time. That's coming from someone who doesn't even know how inductor capacitance works.

>stealing from reddit
baka (shaking my head) tbqh (to be quiet honest) senpai (family)

>>7657000
>stealing from reddit

I was going to say "I found this picture on an unmentionable website" but decided it's not worth mentioning.

Reddit made some good points in their comments. Then again, it's a science sub so it's not really the worst place to go if you're on that site. Though I feel like reddit effectively killed Slashdot and sucked up a lot of it's users.

>>7656983
What book is this?

>>7657006

Herman, Stephen L. Delmar's Standard Textbook of Electricity, Sixth Edition. 2014

The answers at the back of the book are wrong.

For 2a, it should be 2q^8, not 2q^2. Wrong notation.

reddit is better than /sci/ at this point

>>7657072
There's really nothing wrong with /r/science or /r/askscience. There's a lot more information there, too. If I just posted the OP pic here and said, "I found this in my textbook. Is this true?" I doubt I would get anywhere near a lengthy answer as >>7657003

Not that the purpose of this thread was just to repost some image. Just a textbook thread. But you know what I mean.

I have a photograph of this very page. Are you me, OP?

Though actually, check out
> http://www.feynmanlectures.caltech.edu/I_15.html
Find the phrase "Bridge Lab," read the sentence, and read the footnote.

But obviously that's not what Delmar meant.

>>7657012

2a. You mean 6q^5÷3q^3?

What's wrong with the answer? You divide the coefficients and subtract the exponents. The correct answer IS 2q^2.

mirrors are denser at the bottom because glass flows

>>7656983
not a science textbook but this gem is from the first page of my pre-renaissance humanities book. i wrote and angry email to the editors like the sperg i am but got no response

>>7657563
They'll probably correct it. It's not like they'll respond to it if you were a sperg about it.

>>7657012
Hahaha damn son

>>7656983
As a cusoms officer we are always intercepting standards and guide books - the worst are the aerospace, military, medical and EE guides, printed in the far east, sold cheaply in the west but with incorrect data in them.
Free online texts REALLY annoy me, they are scans of bad copies of bad copies of texts - again the worst is EE, guess because its so widespread, a big money spinner.

>>7657761
why would you be intercepting those?

during second year animal physiology courses, we found an errors in an officially rcommended textbook regarding the procedures during digestion, but I couldnt be asked me what it was exactly, some small detail with digestion of fats and bile secretion.

>>7658210
I'll second this.

Textbooks are expensive as fuck, is it really an issue if people are counterfeiting them at schools?

>>7657178
better link:
http://www.feynmanlectures.caltech.edu/I_15.html#footnote_source_1

>>7657239
There's a reason that division symbol is not used often. It's ambiguous. Per PEMDAS the correct procedure would be to divide 6q^5 by 2 and multiply the result by q^3 which would give 2q^8. Multiplication and division have equal precedence so the operations are carried out from left to right.

>>7658245

>Divide by 3, not 2. The point still stands though.

>>7658245
You are technically not wrong, you're just autistic.

>>7656983
Holy shit I've never laughed this hard. OP's pic is gold

Mildly related: T-shirt geometry gone wrong.

>>7656997

It seems to me that whoever wrote that section and created that image or described it to be made, was under the impression that electrical impulses travel "instantaniously" instead of significantly slower than light, which is the reality of things.

Perhaps it's because on the scale of a desktop device and with only the measurement of our eyes, there seems to be no difference between the speed of electrical impulses, the speed of light, and infinite speed.

That they don't understand enough of relativity to know of the non-existance of true simultaneity is likewise troubling.

>>7657012
Only dumb britbongs take division before multiplication.

>>7658245

There is a thing called context.

>>7658256
If I understood the retarded claim he was gonna make before he explained it do I have autism as well, or have I just been on this board too often as of late?

>>7656983
raged

They're talking about group velocity without mentioning the term. The group velocity can in fact exceed the speed of light, as can the phase velocity.

>>7657305
People actually believe this too

>>7657162

> I doubt I would get anywhere near a lengthy answer as >>7657003

You want one? Fine.

As I say in >>7658671, they're talking about group velocity. You could say that group velocity is a measure of how ridged in the traditional, layman sense of the word a given medium is.

The reddit post mentions how the maximum group velocity is the speed of sound in the medium;

>http://www.mtsu.edu/~wroberts/Sound%20beyond%20the%20speed%20of%20light%20Measurement%20of%20negative%20group%20velocity.pdf

Which can be infinite, or negative. So, the perfectly ridged rod required to transmit an FTL signal exists. Moreover, there's astronomical evidence for natural FTL rods in the form of the M87 jet, which has to be at a 19 degree angle to be explainable with relativistic effects but which is coming at us at a 43 degree angle;

>http://iopscience.iop.org/article/10.1086/307499/pdf
>HUBBLE SPACE TELESCOPE OBSERVATIONS OF SUPERLUMINAL MOTION IN THE M87 JET
>The fastest speeds we observe require a Lorentz factor y > 6 for the bulk flow and a jet orientation within 19° of the line of sight, in the context of the >relativistic jet model

>http://articles.adsabs.harvard.edu/full/1995ApJ...447..582B
>Detection of Proper Motions in the M87 Jet
>Constraints derived from the observed motions, as well as the appearance of a sharp edge in knot A, suggest the jet is oriented about 43° from the light of sight

Dark matter is hypothesized to exist at the cores of Earth, the sun or the supermassive black hole at the center of the galaxy. A halo of dark matter is thought to exist around the galaxy as well. Primordial black holes are an explanation for dark matter, and it's been hypothesized that all particles are black holes;

>http://www.technologyreview.com/view/413483/could-all-particles-be-mini-black-holes/

The vacuum is composed of dark matter, and an ultra-sparse, ultra-stiff conductor of gravity, sound and W an Z bosons.

>>7658245
There's also the problem later on of taking it as multiplication of the inverse on the left or on the right.
For example, given two elements a, b of a set, if we were to consider a ÷ b, this is highly ambiguous.
Does this mean a(b^-1) or (b^-1)a?
both of which do not necessarily need to give the same answer.
So regardless of PEMDAS, BIDMAS or whatever you want to use, the ÷ is always a bad choice.

>>7658702
>group velocity.pdf
Stopped reading at
>themselves

>>7656983
the thing this textbook doesn't understand is that force travels at the speed of light, so even if you had a long tube of non flexible tennis balls, it still would take some time for one to come out on the other side.

>>7657012
>ambiguous notation
why is that book not in your trashcan?

>>7658759
Orly?

>>7656983
A lot of textbooks list ribosomes as organelles but they aren't. They're just ribonuclear proteins. Always kind of bothers

>>7658746
>force travels at the speed of light
No... in this case, it would be at the speed of sound of the material through which the force is being transmitted.

>>7656983
Is that a middle-school textbook ? ameritard education is a joke

>>7659188
Unfortunately, I'm assuming that is a highschool grade text for physics.

The only thing that saved me from this fate was that my HS physics teacher had his PHd in astrophysics and genuinely loved teaching, so he made sure we learned it right. (dude was honestly the reason I made it through college; board regulation said you cant weigh a HS final more than 15% and that they cant be more than 1.5 hours - He gave us 40% finals that were 4 hours because he didn't want out first real exams to be in uni. Also his wife was the calculus teacher at the same school. Most adorable coulpe ever, but i digress.)

Most HS teachers don't understand physics beyond the math concepts which the formulas use and wouldn't even pick up on something like that being conceptually wrong. Sad state of affairs.

>>7658799

I dunno, organelle isn't a term with a very specific definition, it could be used to mean any significant subcellular structure that has some function

What about other -somes? Lysosomes and peroxisomes are considered organelles, they have a bilayer membrane and a internal lumen but centrosomes don't have either and are considered an organelle, centrosomes seem more similar to ribosomes. Also vesicles are similar to lysosomes and peroxisomes but their internal protein content is different but they are not considered organelles.