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Anonymous

QTDDTOT 2015-10-06 14:08:05 Post No. 7573555

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QTDDTOT 2015-10-06 14:08:05 Post No. 7573555

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Questions That Don't Deserve Their Own Threads

>Post all your /sci/ related questions here.

>Thread for all small Qs&As

>>

>>7573555

does homework help count?

You're supposed to use the Zwall*A = N/4v * root(8RT/piM) but the numbers don't work out when solving for N.

>>

dumb question, i realize, but why are 1 and 2 in this order? they both have 2 significant resonance structures, so is it the fact that the charge is on oxygen that pushes 1 over 2?

>>

What is the difference between this thread and the stupid questions thread?

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>>7574266

Look at the oxidation numbers on both thw n and the o, your intuition is correct but wont get the marks.

>>

if i have a ship going at over half the speed of light

and another going that speed in the opposite direction

if i stand in one of the ships, will i not be exceeding the speed of light seen from the other ship?

>>

I'm studying Geology and I have the chance to do a 2 week study abroad in Antartica. Should I do it?

>>

do iterated integrals always return volume beneath a surface over a region? what is the difference between double and iterated integrals?

>>

>>7574487

Fuck yes. Only two weeks, probably looks sick on a resume as well (not too sure, don't work in a field relative to Geology). Just seems like something you should never turn down.

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>>7574482

No you wont.

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why does e^i*pi = -1

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>>7574526

The only caveat is it's not exactly "in" antartica. We'll be on a boat making landings and such.

Here's the itinerary: https://osa.isp.msu.edu/Programs/program/index/106798

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>>7574534

Because e^(i*x)=cos(x)+i*sin(x)

>>

>>7574487

DO IT

Saw a job posting for an HVAC engineer in Antarctica, almost made me wish HVAC was my field. Almost.

>>

Does Helium gas in a tube that has a current applied to it glow close to white, but very slightly pink, because its outer most orbital is full?

I was just wondering since elements like calcium are white for that same reason.

>>

What math will help me with programming?

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>>7574482

Have a look at this:

https://en.wikipedia.org/wiki/Relative_velocity#Parallel_Velocities

Taking c to be 1, so v1 and v2 are 0.5 and -0.5 respectively, would give a value of 0.8.

So both objects would see the other moving towards them at 0.8c or 240,000 km/s

>>

>>7574534

Study the Taylor Series. Because:

e^x = x + (x^2)/2! + (x^3)/3!...

sin(x) = x - (x^3)/3! + (x^5)/5! - (x^7)/7!...

cos(x) = 1 - (x^2)/2! + (x^4)/4 - (x^5)/5!...

So try replacing e^x with e^ix in the series and see what you get.

>>

>>7574602

Discrete mathematics

Number theory

Linear algebra, sort of depending how high you go.

>>

>>7574592

You know you can google this, right?

And no, definitely pink

>>

Imagine that we had super-advanced observation tech and could explain all of the universe's forces and such.

Now imagine if we measured and mapped out the location, energy, momentum, etc. of every single thing and modeled it in such a way that we knew with 100% accuracy that some event would happen. For example, they predict that in one minute, somebody would sneeze.

Now what if they killed that person, right then and there, making them unable to sneeze? That wouldn't be possible, I would think, since they determined that the universe would act in that way, but they made it not so.

I have two possible explanations for this:

1. Due to the uncertainty principle, we can't measure and predict things like this

2. The universe is not deterministic

Or a combination of the two. Assume that we have the available computers and physics to compute the information, given that we can obtain it.

>>

>>7574620

>post all your /sci/ related questions here.

>>

just by looking at a function how can i tell if the limit is either approaching a number or either negative or positive infinity. Pic related I can easily take the limit of either left or right hand zero. And see if the limit exists and get some type of infinite. Or I can manipulate the function like the picture did. What the fuck /sci/ why cant any teacher be clear on this for me.

>>

Is \sin^0(x) = x or is \sin^0(x) = 1?

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>>7574651

Even if the universe were deterministic and the uncertainty principle was not law, the scenario you present would not be possible because the simulator cannot exist.

The simulator, to accurately simulate the universe, must also simulate itself. Were there a machine that could simulate itself with extra computing power left over, it could play all sorts of paradoxical shenanigans with the universe.

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>>7574833

That's a good point I didn't consider.

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>>7574819

It equals 1 for x \neq \pi n

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>>7574811

this is a 0/0.

You have to use l'hopitals rule fam.

The answer is 1/6

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>>7574811

L'R is just a quicker way of doing it. I'm talking about either doing it analytically ergo. -.0000001 for left hand limit and .00000001 for a right hand limit as H---->0 or doing it algebraically by using the conjugate. Lets just say I cant use L'R for a test.

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>>7574139

I didn't trust your formula anon, since you said it didn't work for you, so I worked it out from first principles using the Boltzmann distribution, and I got answer

N = \frac{4 V (\frac{dN}{dt})}{A} \cdot \sqrt{\frac{\pi\ m}{8 k_B T}}= \frac{4 (22.7 L)(1 m^3/1000 L) (2.25 \cdot 10^{15} atoms\ sec^{-1})}{(1.63 \cdot 10^{-11}\ m^2)} \cdot \sqrt{\frac{\pi\ (4.0026\ Kg/1000\ mol)}{8 (8.31445\ JK^{âˆ’1}\ mol^{âˆ’1}) (298\ K)}} = 9.98 \cdot 10^{21}\ atoms

>>

Someone want to help me with my homework and explain how I know which of these resistors are in series and parallel?

>>

>>7574966

This is what I got using ThÃ©venin's method (or at least my interpretation of it):

Assuming an open circuit at CD, it's relatively easy to getV_{Th} = \bigg( \frac{R_3}{R_3 + R_4} - \frac{R_1}{R_1 + R_2} \bigg) V

Assuming short-circuit at CD, after a some messy algebra,R_{Th} = \frac{R_1 R_2}{R_1 + R_2} + \frac{R_3 R_4}{R_3 + R_4}

So then I gotI_{C \rightarrow D} = \frac{V_{Th}}{R_{CD} + R_{Th}} = \frac{\frac{R_3}{R_3 + R_4} - \frac{R_1}{R_1 + R_2}}{R_{CD} + \frac{R_1 R_2}{R_1 + R_2} + \frac{R_3 R_4}{R_3 + R_4} } V

I also did the problem using only Kirchhoff's loop and junction laws, and got the same RHS of the last equation. So I think it should be correct.

>>

>>7573555

I always wake up on weekends thinking "Today im going to revise this for an hour"

Then I get on my PC and load up a game or something

I have little to no self control to make myself revise, and I dont want to uninstall games because its the only thing stopping me going insane after a 10 hour day at college

How do I develop my self control?

>>

>>7574966

Two resistors are in parellel when they have they are connected to the same points A,B and share the same voltage. Two resistors are in a series when they are connected in this way A-R-B-R-C and the current through each is the same. http://www.allaboutcircuits.com/textbook/direct-current/#chpt-5

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>>7574956

Thank you kind sir!

>>

If someone else is asking the different between a Gaussian and a Poisson distribution curve. Is it a safe laymans way to say that the mean of the Gaussian curve is static with evenly distributed data around the mean, where the mean of a Poisson curve "isn't fixed", or "moves", and the data is not evenly distributed around the mean with no central tendency? Does this make sense?

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>>7575246

Poisson distribution isn't always like that anon. It can sort-of look to have a central tendency, more-or-less, depending of the Î» parameter. See Î»=10 in image below.

Also Poisson dist is a discrete distribution (with continuous analogs) whereas Gaussian is a continuous distribution (with a discrete analogs).

I'd just show them the wiki pics.

https://upload.wikimedia.org/wikipedia/commons/1/16/Poisson_pmf.svg

https://upload.wikimedia.org/wikipedia/commons/7/74/Normal_Distribution_PDF.svg

>>

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>>7575261

So I think I'm right in assuming my data follows a Poisson curve. I have a variable amount of patients that I visit per day , and I'm documenting how many of them I actually get to enroll in a particular trial. On the X axis I have the number of patients enrolled, and on the Y axis I have the Poisson probability of any number of patients enrolling. My mean is 9.22222222. This is just me documenting my productivity and success rate for my own personal portfolio and records.

There is not a fixed amount of patients I see however, I could see 10 I could see 50. Does that matter?

I'm trying to make sure I have it right before I do it wrong for the next 10 months, plus I'm sure I'll have to generate a report and presentation for my CIO when I look for advancement.

>>

>>7575261

One more thing I just thought of, since I don't see a fixed amount of people per day, should I use the proportion or percentage of successful enrollments per day? I feel like that would give a clearer representation of my success versus raw enrollment numbers.

P.S Sorry, it has been a while since I've done stats like this and even in my Stat 250 class we never covered Poisson, I was only exposed to it in Ecology.

>>

>>7575275

Never-mind, answered my own question using excel. When you use the Poisson equation on values {<1, >0}, doesn't give a distribution at all.

Derp.

>>

>>7575272

>>7575275

It's hard to say whether your data should theoretically fit a Poisson distribution (of course it approximately will, but it may better fit to another distribution) But does it really matter?

It sounds like you plan to do a thorough job in keeping good data. You can try to fit a Poisson distribution to your data once you have built up some statistics first. Also, if you keep track of how many patients you saw as well as how many successes you had, you can present the data both ways (as a overall percentage as well as raw numbers). (Bosses love percentages BTW.)

I guess what I am saying is, since you plan to keep good statistics, why not let the data speak for itself instead of trying to shoehorn it into a paradigm beforehand?

>>

>>7575288

Oh yeah I have all of the simple stuff like percentages and whatnot already neat, tabled and graphed. The first tab of my excel file is all equations that build up as I fill in the next 12 tabs which are each month.

Also, to be honest about "trying to showhorn it into a paradigm beforehand", I'm just trying to brush up on my mathz because I'm curious and I have time to kill at my desk in the mornings.

Thanks again for your help though.

>>

Why does a neutrino transforming imply that it has mass?

>>

Good book for probability theory? (introductory)

I have Jacod Protter but it seems too terse. Any other suggestions with examples and excercises?

>>

>>7575463

Rick Durrett: Probability: Theory and Examples

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>>7575478

Thanks anon.

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>>7575181

Thanks!

>>

Why and when did scientist decide on 360 degrees as the standard?

>inb4 it's convienent

>>

>>7575560

Same question except, why to we use a p=.05 in stats? What the fuck is so special about 5?

>>

Although algebraic and transcendental numbers aren't element of Q, why wouldn't we be able to find a numerator and denominator down the line that gives us an algebraic or transcendental number?

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>>7575560

The division of the circle into 360 degrees comes from Babylonian astronomy. A year is approximately 360 days (= 12 months of 30 days), so the sun appears to move about 1/360th of a revolution around the celestial sphere over the course of a year.

Also the convention that an hour is divided into 60 minutes and the minute into 60 seconds comes from the Babylonians too. They used a sexagesimal (base 60) number system for their mathematics and astronomy. They got this number system from the ancient Sumerians who developed it as early as 3500 BC.

>inb4 it's convienent

The number 360 has lots of divisors. It is much more convenient than our modern (Gregorian) value of 365.2425 days per year. Imagine learning geometry and trigonometry with 91.310625-degree right angles (instead of 90) and instead of 30,60,90-degree triangles you had 30.436875,60.87375,91.310625-triangles. The Xbox 365.2425 has a nice ring to it though.

>>7575569

I'm guessing this probably goes back to Jerzy Neyman's original confidence interval paper in 1937. The 5% level of significance of (p-value 0.05) seems often to be chosen in softer sciences where it is harder to get good data. But in biological science papers I often see 0.01 and sometimes 0.02 values reported as well. In particle physics we usually use a 5-sigma (about 1 in 3.5 million) significance level for reporting the discovery of new particles.

>>7575806

No anon, algebraic numbers include ALL the rationals too (because if a,b are integers with b =/= 0 then p(x)=b*x-a=0 has the rational root x=a/b). Transcendental numbers are defined as all the complex numbers that are not algebraic, so by definition no number can be rational and transcendental.

>>

So you can determine the redshift of a galaxy or star or whatever by spectroscopy I get that. What I don't get is 1) how do we know what we expect the SED for a certain object to look like and 2) how do we know which emission lines on an observed distribution are which?

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>>7574139

If by Zwall you mean particle loss rate it looks like your dimensions are wrong m8. Think about where the area A should be.

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>>7575898

sorry, should've specified that by algebraic I meant radical, and by transcendental I meant e or pi

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>>7574819

>Is sin0(x)=x or is sin0(x)=1?

It could be either one, depending on the interpretation of the superscript.

In function iteration, the superscript indicates how many times the function iterates on itself. Any function iterated 0 times always yields x.

The other interpretation is power. Anything to the 0 power is 1.

This is an ambiguous area because for the trig functions, a superscript of -1 is treated as function iteration; whereas a superscript of 2 or higher is treated as power. I don't believe there's a standard interpretation for a superscript of 0.

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>>7575902

\begin{equation}

\vec{x}=A^{-1}\vec{b}

\end{equation

>>

>>7575298

Why does a neutrino transforming imply that it has mass?

In quantum mechanics the possible values/states of a physical quantity are given by the eigenvalues/eigenstates of its quantum mechanical operator. For example, a propagating particle (any physical system, really) has an operator associated with it called the Hamiltonian. The eigenstates of the Hamiltonian determine the energy that a particle may be observed to have. Energy eigenstates are important, because they are stationary. That means if a particle is in an energy eigenstate, it will generally stay in that state. Other physical quantities don't necessarily behave in this nice way. If a particle is not in an definite energy eigenstate, but say a starts in a definite position eigenstate, it will then be in some mixture of energy eigenstates and it will oscillate between position states in a complex way determined by the SchrÃ¶dinger equation.

Separate from this there is a quantum theory called SU(2) electroweak theory which describes the weak nuclear interactions of particles called leptons. There are three "flavors" of charged leptons called: the electon, muon, and tau. Electroweak theory says that these charged leptons have to have certain uncharged SU(2)-partners associated with them called anti-neutrinos. There is a different anti-neutrino associated with each flavor of charged lepton. These different anti-neutrinos are called the flavor eigenstates.

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>>7576177

>>7575298

Now it turns out that being an anti-neutrino is not so cut and dried. Anti-neutrinos are created in particle interactions with electrons, muons, or tau particles, so they begin life as flavor eigenstates. But the flavor eigenstates turn out not the same as the stationary mass/energy eigenstates. There are three different flavors and three different mass states, but they don't correspond up together nicely. There is a certain U(3) matrix transformation which is needed to switch back and forth between flavor eigenstates and mass/energy eigenstates. Therefore, what starts out life as an electron anti-neutrino, is really a non-stationary mixture of the three mass states, so there will be a complex oscillation among flavors as governed by the SchrÃ¶dinger equation.

So after some time an electron anti-neutrino can actually become a muon anti-neutrino and vice versa. Observation of this phenomenon indicates that there really are three different mass states underlying the time evolution (oscillation) of the flavors.

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>>7575967

>sorry, should've specified that by algebraic I meant radical, and by transcendental I meant e or pi

The point still stands that radicals like -\sqrt{\frac{9}{4}} contain all the rationals. Both e and pi have been proven to be transcendental, which means they cannot be a root of a polynomial with integer coefficients as in >>7575898 . Therefore they can't be rational, so you'll never find those integer numerators and denominators, anon.

(BTW, It's actually much easier to prove directly that e and pi are irrational than transcendental.)

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>>7575910

1) we can directly measure the SED for the different elements (hydrogen, helium) in the lab, and we can also look at the SED of similar nearby astrophysical objects that are not so redshifted as much.

2) it is actually a complicated computational statistics problem, and the astronomers end up doing a sliding best fit over a whole spectral range, comparing to what is expected from 1) in order to determine the best estimate for the redshift.

>>

Can someone point me to a rigorous exposition of the uncertainty principle, i.e. the if-and-only-if relationship between nonzero operator commutator and measurement uncertainty?

Chem major, comfortable with analysis, never took modern algebra

>>

I have two balls. One has a height that is 60% greater than the other ball. Now I need to find how many percentage the volume is bigger. Is it possible to figure it out on this info alone?

Other than that I had a y=b*x^a where a=2.9927 and b=523,68, above it but I don't know if they are related because there is a picture of two balls in between the questions.

I'm afraid to ask my teacher because I'm at least 60% sure it's because I'm not getting the situation.

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>>7576499

>I have two balls. One has a height that is 60% greater than the other ball.

Might wanna smh a doctor tbh fam

>>

>>7574611

I'd put linear algebra at the top. Lots of programming problems can be reduced to matrix operations, if you know how to see them from that perspective.

>>

>>7576508

Cure me doctor.

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>>7574811

For lim -> 0, try using low-order polynomial expansions. I do that all the time, because in physics (I'm a theor. phys.) we often want to know, not only the limit, but how the function actually approaches this limit.

In this example sqrt{x^2 + 9} = 3*sqrt{1 + x^2/9} approx 3*[1 + x^2/18] = 3 + x^2/6

The full expression becomes

(3 + x^2/6 - 3)/(x^2) + terms of order x^2

= (1/6) + terms of order x^2

The limit value of 1/6 appears naturally; just make x = 0.

The power series expansion I used for the square root is based simply on Newton's binomial theorem. I put it in the form sqrt{1 + something} because it's easier.

>>

>>7576510

markus?

>>

>>7576441

Do you mean something like this anon:

http://quantummechanics.ucsd.edu/ph130a/130_notes/node188.html

>>

>>7576499

Are you saying that the diameter (D) of one sphere is 60% larger than the diameter (d) of the other one? If so then we can say say D=1.6*d .

Since the volumes are V = (4*pi/3)(D/2)^3 and v = (4*pi/3)(d/2)^3 we can say V/v = (D/d)^3 = (1.6)^3 = 4.096 which is 309.6% bigger volume.

>>

How much would a 40x objective lens on a compound microscope cost to replace if someone mistook it for a 100x and got immersion oil on it?

Asking for a friend here.

>>

>>7576655

Actually yes. Thanks anon.

I understood all of it except the step in pic related. Why does that difference of inner products equal the inner product over the commutator?

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>>7576740

Oh it is just this anon:i \lambda \left<U\psi \vert V\psi\right> - i \lambda \left<V\psi \vert U\psi\right> = i \lambda \left<\psi \vert U^{\dagger}V \vert \psi\right> - i \lambda \left<\psi \vert V^{\dagger}U \vert \psi\right> = i \lambda \left<\psi \vert U^{\dagger}V-V^{\dagger}U \vert \psi\right>

And presumably we are working with physical observables, which are hermitian

U^\dagger = U \ \ \ \ \ \ V^\dagger = V

>>

>>7576724

Fuuuuuuuuu

ethyl alcohol and deionized water, anon?

>>

I just started freshman year of university.

I'm currently an environmental science major, but I want to know how important is accreditation?

Like if I wanted to switch to biology, but it's not accredited at my university is it stupid? Would I not be able to go to graduate school or anything?

Also economics is accredited, and a really good program here, and I love that subject as well, but I'm not sure.

Anyone with experience in any of these fields? Share some knowlege about accreditation and graduate school/work?

>>

What software should I use if I want to quickly try out stuff with optics?

I suppose I could always use LuxRender with patterned lights and some fog, but that means it'd take 12 seconds for me to see the ray paths of each setup.

>>

>>7576791

The ops are linear

>>

Is the space flooded with harmful radiation in general, or is Mars' problem only sun-related?

>>

>>7576864

Mars has 55,000 lux of sunlight, and 0.001 lux of starlight.

Given that the harmful radiation propagates in the same way as visible light when a significant atmosphere is lacked, this will mean that this also approximates the ratio of harmful radiation from the sun to harmful radiation from space.

Could be wrong by an order of magnitude or two, but even then, the difference would still be huge.

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>>7576791

Why does the first equality hold?

>>

>>7576853

>>7576993

Yep, QM is done with linear operators acting on state vectors in a complex Hilbert space. The inner product on the Hilbert space has the property that

\left< \phi \vert A \psi \right> = \left< \phi \vert A \vert \psi \right> and \left< A \phi \vert \psi \right> = \left< \phi \vert A^{\dagger} \vert \psi \right>

\dagger[\math] represents the Hermitian conjugate. See https://en.wikipedia.org/wiki/Hermitian_adjoint .

>>

>>7577063

latex failed when i tried to say

\dagger represents the Hermitian conjugate. See https://en.wikipedia.org/wiki/Hermitian_adjoint .

>>

Reading the top answer to

http://photo.stackexchange.com/questions/69873/how-to-explain-that-the-jpg-digital-file-of-my-photograph-isnt-free

reminded me of how people immediately feel required to discuss your plans, when you explain why you can't meet them/have to leave early/etc.

So, my question would be what do call these almost ritualistic exchanges in human communications?

>>

When a light bulb is shut off in a room where do the light(photons?) go? Do they get transformed to heat and absorbed into walls, furniture and other objects?

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>>7577393

yep you answered your own question anon. and you know what? it all happens ....

...

...

...

(wait for it)

...

...

...

at the speed of light!

>>

>>7577393

The light doesn't go anywhere, it's simply not emitted anymore. The filament glows because it has a high temperature (due to the current passing through it). When you shut the current off, the temperature of the filament drops so no light is emitted.

>>

>>7576804

I've never gotten immersion oil on one before and they don't give us protocols for fixing the situation. I wiped it off as well as I could with lens paper, but by the end of the lab period, the lens had pretty much half the light getting through it, and it wasn't focusing properly.

I'm awaiting an email from the TA, but in the case that I don't get one, that means they just moved all the microscopes into the inventory room and didn't keep track of which one went to which lab group.

However, on the chance that I do get informed I was possibly responsible for ruining perfectly good equipment like the retard I am, I would still like to know how much they cost. I can't ask anyone because that will make me look more suspicious and google isn't really helpful, so anonymous imageboards are my last resort I guess.

Srsly, any biofags know how much these cost to replace?

>>

>>7577411

divided by the refractive index of the air in the room

>>

>>7573555

OKAY SO to think if there really was lifeforms on another planet would it really be so different to our own

like mammals insects arachnids etc would plantlife still be green

What could be factors that change the way we are.

>>

How does AC current work if a sine wave always averages out to 0? i.e I take 5 steps forward and then 5 steps back I'm in the same place as before and no power has been transferred

>>

>>7577072

I assumed the dagger denoted the adoint, just wasn't familiar with that property of hilbert spaces. My book is at a fairly low level of abstraction. Thanks

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>>7578067

It's still the speed of light in the medium, even if it's not c.

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>>7578192

Because circles

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>>7578355

holy shit I'm an idiot. Thank you anon

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>>7578365

I was trying to troll you by giving you the right answer in an unhelpful way, but it looks like you got it. Nice. Anytime, bro

>>

are electrons, protons and neutrons actually little balls of mass? or is that the most convenient way to represent them? also do humans know how quarks move in sub-atomic particles? do they orbit around each other or touch?

>>

>>7578374

gave me a flashback to phase diagrams and stuff from high school

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>>7578379

quarks are held together with the weak nuclear force (look into gluons, some weird shit there), which increases in strength with distance.Quarks can only exist in pairs, come in different 'flavors', and are usually considered point-like. The elementary particles are hard to imagine, but they do have radii and such so they are little balls of mass in essence.

Maybe that answers some of your questions

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>>7578501

scratch that weak force

also everything we know of quarks is from observing their effects because it is impossible to isolate a quark

>>

How can mirrors be real if our eyes aren't real?

>>

>>7573555

how do I become an ornithologist?

>>

Recently I have begun to shit more frequently. I don't have diarrhea, the shit is still solid and I do not experience stomach pains. However, instead of coming out in one huge turd it comes out in pieces, like rabbit droppings. It might have something to do with my diet, I'm not sure. Not too long ago I have begun been eating salmon and asparagus once a week, but other than that my diet has remained the same, and the symptoms occur all throughout the week and not just when I eat those things. Is this anything I should be concerned about?

>>

>>7580048

I couldn't tell you. If you can afford the pointless trip a doctor is always willing to tell you that nothing is wrong, or you need to pay them more if you want to get a test.

>>

>>7573555

is it possible to have two relations f and g such that f(g)=g(f)?

>>

>>7580048

Just sounds like constipation. Drink more water I guess

>>

I don't know if this question will make sense to you, but here it goes:

I want to learn physics but I currently only have a very basic understanding of mathematics. Currently as it stands, I only have knowledge up to algebra (not very good, I know). In what 'order', for lack of a better term, should I learn different areas of math in order to build up to physics to where I can start practicing problems and learn from there? What I'm asking, generally speaking, is what areas of math must be learned in order to start learning physics? Thanks in advance.

>>

>>7580226

I'd try and find a high school text book that teaches the basics and learn things such as (off the top of my head):

Algebra

Quadratics/parabolas

Derivatives

Integration

After learning these I'd pick up a basic physics text book and start going through. Basic Newtonian physics starts with pretty basic algebra, adding in some quadratics and then calculus (from memory at least). If the text book has anything beyond that simply learn them as you go

Khan academy teaches these mathematical concepts pretty well but you'll probably need work sheets to consolidate your knowledge though (or something like Math Online; can't vouch for it myself though)

>>

EASY QUESTION: 1D MOTION AND THERMODYNAMICS

I still can't get it though.

>"What must the initial speed of a lead bullet be at a temperature of 30.0 âˆ˜C so that the heat developed when it is brought to rest will be just sufficient to melt it? Assume that all the initial mechanical energy of the bullet is converted to heat and that no heat flows from the bullet to its surroundings."

Check pic for my working and tell me how I'm not right. The answer is apparently 355m/s.

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>>7580446

did you take into account the heat required to melt it? just bringing it to the melting point won't fully melt it.

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Is there a mathematical proof for the Earth being round? /x/ is being retarded again.

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>>7580460

Wow you're right. I forgot that latent heat of fusion is a thing.

Thank you kind stranger.

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>>7580446

You've calculated the energy required (and the speed by extension) to heat the bullet to its melting point, 327.5 C.

You need to account for the energy required to actually MELT the bullet. Melting does not happen spontaneously upon a temperature being reached. Pic very related, it is a graph of temperature vs time for a constant input of energy into matter. Note that it plateaus as energy is being added at the same rate, but it is being used to change the phase of the matter instead of simply heating it.

From google the latent heat of fusion (melting/fusion phase transition, it is different for other phase transitions) lead is Lf = 22.4 kJ/kg, so your new equation is

0.5mv^2 = mcAt + mLf

v = sqrt(2*cAt + Lf) = 349m/s by my TI-84 but your hmrk might use different constants

L

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>>7580110

>is it possible to have two relations f and g such that f(g)=g(f)?

functions can't take functions as arguments.

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>>7580462

is there a mathematical proof that your face isnt ugly?

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>>7580520

Probably tbh m8.

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>>7580542

very cool, thanks fam

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In this site: http://4chan-science.wikia.com/wiki/Mathematics

There are some great problem books. The physics page doesn't have any problem books, is there any site/list of problem books for physics? I can't learn without doing exercises.

Also, related to PatrickJMT, should I use his Calculus videos with Spivak/Apostol for a better understanding or I can drop the books/video?

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This is sort of an /o/ related question

Why is it so hard for car designers to make an aerodynamic vehicle? Even with wind tunnels and ass loads of computer renderings, etc we still come out with very 'meh' cars aerodynamically? Is it because we don't know enough about how aerodynamics work?

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>>7580503

Thanks L, confirmed my working.

Anyone want to figure out another basic physics question?

>A slab of ice floats on a lake, what minimum volume must it have for a 55kg woman to stand on it without getting her feet wet?

Density of ice = 934kg/m^3

Density of fresh water = 1000kg/m^3

I used the equation:

(55*9.81) + (934*9.81*X) = (1000*9.81*X)

which simplifies to:

539 = 9810X - 9162X

X = 539/648

X = 0.83 m^3

to signify the point at which the ice block with the woman is floating just at the surface of the lake. this is wrong, apparently. The weight of the woman plus the ice block should equal the weight of the displaced water, correct?

plz respond

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I'm so sorry. I know these are troll, guaranteed response pics. But this one just triggered me.

I'm in elementary statistics and we just started binomial probability distributions. I saw this picture and I thought, what a chance to see the method I learned in action. And it appears, by the method I've been taught, the slower weapon is going to be more reliable.

We have a table we can follow where we go by number of trials, number of successes, probability of a success... and according to that table, for 4 swings of the weapon with the 10% hit rate, we've got a 34.5% chance for at least one success.

How can it be so? Why is it not 40%? Does it have to do with some kind of margin of error that is assumed when using such a table?

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>>7580714

>according to that table

Why don't you just calculate it by hand

Also, the faster one is more reliable since it has a smaller variance and the same mean

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>>7580613

You should be comfortable with cookbook computation for undergraduate physics. Books like Stewart aren't great as -books-, but make decent cookbook problem sets.

I'd recommend Spivak over Apostol quite strongly. It's far less dry, has a coherent, inspired view of what he's trying to teach, and is the best option a non-mathematics major has for a theoretical understanding of calculus. It's one of the better introductions to proof based math a non-mathematics major can have imo, and it will give you an early sense of whether or not you want to pursue mathematical physics.

>>7580714

If you swing red three times (12 attacks) is it 120% likely you get at least one hit?

You need to consider the probability of no hits (.9) at each attack. Since these are independent, the probability of no hits after two attacks is .9*.9=.81, and after n attacks is (.9)^n.

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>>7573555

Got these niggas on my dick

Like I'm so swag

Bitches in this shit- she a big booty kaffir

Why is it that isoforms hardly differ?

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>>7580746

OK, I think I'm closer to understanding

it seems the slower weapon is more reliable for the first several swings but at some point the faster weapon pulls ahead

fascinating

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>>7580797

the faster one is always more reliable...

i dont know what you're doing

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>>7574578

that makes sense

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>>7580777

Aw come on, I got trips. Why is it that isoforms of proteins hardly differ in terms of physical properties and biological functions?

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>>7580620

http://www.eternalmachinery.com/mostaerodynamic/

try turn this into a completely flush, ultra smooth car. Its not worth it

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>>7580805

actually I'm showing the slower weapon more reliable always

I'm using binomial probability formula (pic related), well I'm using my ti graphing calculator's function for that formula to make it faster, but I've tested it to the formula I have and I get the same results

I use x=0 to find P(0), the probability that there are no successful swings. Then 1-P(0) gives me the probability that there is at least one successful swing.

for instance let's look at 4 seconds

for the slow weapon, we're looking at 4 attacks in 4 seconds, so x=4

40% hit chance so p=.4

for no successes, I input:

binompdf(4,.4,0)

=.1296

so the chance of at least one successful hit = 1-.1296= .8704

87.04% chance for at least one successful hit in 4 seconds with the slow weapon

now the fast

16 swings in 4 seconds, x=16

p=.1

binompdf(16,.1,0)

.1853020189

1-.1853020189= approximately 81.5% chance for at least one successful hit with the fast weapon in 4 seconds

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>>7580110

Do you mean something like this, anon?

Say f(x) = x^2 and g(x) = x^3 . Then

f \Big( g(x) \Big) = f(x^3) = (x^3)^2 = x^6

g \Big( f(x) \Big) = g(x^2) = (x^2)^3 = x^6

So f \Big( g(x) \Big) = g\Big( f(x) \Big) .

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>>7580854

sorry I should clarify

n=trials (swings)

x=successes

p=success chance

format for calculator is binompdf(n,p,x)

I wonder if there is a faster way of comparing the 2 rather than plugging the formula and comparing the difference

I hope I will get better at stats, I have trouble wrapping my head around some of these concepts. Like with this problem I predicted that the 40% chance would yield better results when I first saw the troll pic on /v/, I figured I would go with the slower weapon. But once I try to comprehend why, it confuses the fuck out of me. Same shit happens every class, if I try to actually comprehend the stuff rather than just scribbling notes and churning through examples, I get lost fast. I need some way of wrapping my head around this stuff. I always thought I was good at math but stats kills me.

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>>7580854

I think you forgot to weigh the probabilities.

Let's say we attack for 1 second:

The blue weapon can only hit once and therefore has a 0.4 chance to hit

Now the red one can attack 4 times. If you look at the probability of at least one hit, you're implying that two hits is the same as one hit: you look at the chance to get hit, instead of the damage output.

Let's say the damage of a hit is 1, then the blue one does on average 0.4 damage.

The red one however, does

E(\text{damage}) = \sum_{k=1}^4 k \cdot \binom n k p^k(1-p)^{n-k} \\

= \sum_{k=1}^4 k \cdot \binom 4 k 0.1^k(1-0.1)^{4-k}\\

= 0.4

Which is identical to the blue sword.

So their damage output is equal. Can we still say that one is better than the other? Yes, one is more reliable (has a smaller variance). It's easy to calculate that it's the red one

Hope this helps

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>>7580881

>>7580883

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>>7580881

>>7580884

Yeah, I guess I was getting hung up on the bigger chance of no hits per second for the red sword. But then, it can hit multiple hits per second, whereas the blue can only hit one per second, and yeah, hitting more than once = more damage. I should have figured it would work out to the same damage per second.

I'm not entirely sure how to work out the notation you showed in the pic. Been a long time since I worked with anything like that, my last math class before this elementary stats, was calculus about 12 years ago. If it wasn't 6am I'd work at it myself until it made sense but it's time for me to wrap this up. I'll check the thread when I wake up.

Would you explain why one is more reliable then?

My assumption would be that it equalizes on each second, and in between the seconds the red is better, but can you show me?

Either way, much appreciated for the help you've given me.

Funny... I wasn't in the mood to study for this class tonight, and then I found this pic on /v/ that's relevant to the chapter we just started and that's what got me to study. Always cracked me up how these pics can spawn threads that will go on to bump limit if they don't get cleaned up by janitors. At least this one is better than the order of operations / syntax trolls.

OK, I've spent way too long on this and if I had more spare time in my life I'd write a program to explore it further, but it's time for bed. Thanks again.

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>>7580516

>functions can't take functions as arguments.

You have no idea how incorrect you are.

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>>7574505

>do iterated integrals always return volume beneath a surface over a region

If you're doing an integral of a surface with respect to the area element in a given coordinate system then yes.

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>>7573555

is the earf flat?

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>>7581918

someone got trips on /b/ and declared the earth banana

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>>7581999

on a shroom trip i declared the earth to be a nowhere-differentiable surface

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>>7576807

You should switch to an accredited school

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>>7578109

Different forms of animals only exist given that animals even evolved at all, then differentiated into a certain precursor. So the probability of a particular animal evolving depends on the probability of its ancestors evolving. I think single celled life is pretty likely, multi-cellular life may be likely as well but I think it would be difficult to say what form it would take. I do think photosynthesis would exist, color would depend on the atmosphere and stuff.

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What is the difference in lift in ground effect craft versus traditional aircraft?

Or in other words - how much lift could you remove from a traditional aircraft (say a 747) to still have enough to keep it off the ground thru ground effect?

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>>7581999

I thought you knew.

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