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/sci/ Science & Math

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Most viewed threads in this category

1 more posts in this thread. [Missing image file: waterfall_of_light_by_lairis77-d38ets9.jpg]
Got a physics I problem I'd like some help with if anyone is up for helping a brother out. Just guidance is more than sufficient. It seems like a basic circular motion problem, but I missed the lecture on it when my professor taught it in class. Here's the problem: The angular velocity of a process control motor is w = (20 - .5*t^2) rad/s, where t is in seconds. a. What time does the motor reverse direction? b. Through what angle does the motor turn between t = 0 s and the instant at which it reverses direction? So here's my thought process on this one. For part a), set w (the angular velocity) to 0 to solve for t (where I'm guessing is the point that the motor changes direction). So 0 = 20 - .5*t^2 >> t = sqrt(40) s. For part b), take the derivative of the equation to get the angular acceleration, plug it into Af = Ao + wi*t + .5(alpha)*t^2 to get the answer in radians, then convert to degrees if I want to. I ended up getting -20.13 degrees for my final answer, or 125.49 rads. This question doesn't exist on any website (trust me, I've tried looking) so there is no way I can check my answer (not in the back of my textbook). Any guidance AT ALL will be most appreciated!
51 more posts in this thread. [Missing image file: 1354656462029.jpg]
I was staring at this picture when dad walked past my room, he walked in and asked who these people are. I pointed to Einstein and Curie and said you should know who these two are, he said yes. I then pointed to Planck, Bohr, Lorentz, Schrondinger and Heisenberg and asked again, he said he had no idea. He asked about what they contributed to science, I told him about quantum entanglement (which he had never heard of before), I told him about the constant debates between Einsten and Bohr about determinism and a probabilistic view of the universe, I also told him about quantum superposition. He asked about what quantum entanglement proves, I told him that it could be used for long distance communication, possibly even teleportation. He just nodded and said, good. Then walked off. Did I ruin my chance to explain science to a deepy religious man or was I right when I said entanglement can be used for communication with 0 time delay
32 more posts in this thread. [Missing image file: Aaron_Swartz.jpg]
Ok guys, I'm considering going to a University offering access to the ACS publications, AIP/APS publications, Cochrane Library, EM-Premium, JSTOR, LNCS, MathScinet, Nature, NEJM, Science Direct, Springer, ... I hate all of these paywalls, and since the death of Aaron Swartz, I'm considering doing something to liberate these articles and make them available online. What could we do with my access to these ressources?
5 more posts in this thread. [Missing image file: 1359672788923.jpg]
Hi /sci/. I've been thinking of going to university to study IT whatever you call it in your country. Computers and programming and shit. I know it sounds boring, but I guess I don't want to end up without a job after studying cognitive science or history or some women's subject like Literature. How bad an idea is it to study computer things at Uni? In return, ass.
1 more posts in this thread. [Missing image file: Eric_Dollard_2011[1].jpg]
Is Eric Dollard just crazy or is there really a conspiracy to oust him from the EE community?
0 more posts in this thread. [Missing image file: 1357835489608.gif]
Hey /sci/, I don't usually come to these parts but I am currently stuck at home for weeks on end due to a broken arm and am looking to feed my brain over this out of work period. Long story short I've developed an interest into the evolution of human race, (i.e. the split of races after leaving africa). I'm wondering if any of you can give me some refrences of interesting books, documentaries or online papers. Anything to get me started would be helpful.

quick help

2 more posts in this thread. [Missing image file: 1353138843613.gif]
>A force in the -direction with magnitude F(x) = 18N-(0.53N/m)x is applied to a 7.40kg box that is sitting on the horizontal, frictionless surface of a frozen lake. F(x) is the only horizontal force on the box. >If the box is initially at rest as x=0, what is its speed after it has traveled 17m? I'm using the equations a = F/m = (18 - 0.53x)/7.4 and a = (mv^2)/2 V(f)^2 = V(0)^2 + 2a(dx) = 0 + 2a(17) So I get v = 6.43 m/s, but apparently it's wrong. Can you guys help me out?
6 more posts in this thread. [Missing image file: mag.png]
Can a magnet attract a positively charged piece of plastic?
8 more posts in this thread. [Missing image file: osmosis2.gif]
Sci can you help me with some general biology questions on cellular osmosis? yes i know i am not that smart 1. Explain what happens to a cell, in terms of osmosis (not just ordinary diffusion), if it is immersed in a solution which has a greater concentration of solute particles (hypertonic) than that inside the cell. (Assume water is the solvent) 2. Explain what happens to a cell in terms of osmosis if it is immersed in a solution which has a concentration of solute particles that is the same (isotonic) as inside the cell. 3. Explain what happens to a cell, in terms of osmosis, if it is immersed in a solution which has a lesser concentration of solute particles (hypotonic) 4. Name and explain at least two mechanisms or adaptations by which a cell can regulate possible harmful effects due to adverse osmotic conditions. a. b. 5. Name and explain two instances in which the effects of changes in osmotic pressure are seen in everyday life (not necessarily in a biology laboratory) a. b. ?
5 more posts in this thread. [Missing image file: 1360100128025.jpg]
Guys i need some help on this problem, it's not homework, i just want to know if i'm doing this right. Basically, i have this sequence of functions: f_{n}(x) = \frac{n(1 + x)^2 - 2x^2}{nx(1 + x)^2} First of all i have to find the punctual limit of this, and it's pretty easy to find that it's \frac{1}{x} Next thing i have to do is determine if the series \sum_{n = 1}^{\infty}f_{n}(x) converges in some point of \mathbb{R} - \left \{ 0,-1 \right \} Now, it is true that a series of functions, like a series of numbers, doesn't converge if the general term f_{n}(x) doesn't go to 0 when n goes to infinity. In this case, as f_{n}(x) \rightarrow \frac{1}{x} as n goes to infinity, does this mean that the series cannot converge in any point as 1/x is never 0?
15 more posts in this thread. [Missing image file: 1358629667202.jpg]
Check the boxes beside the statements that are TRUE, regarding force and motion. Select all that are True. 1 If an object's speed does not change, no net force is acting on the object. 2 In order to not slow down, an object moving at a constant velocity needs a small net force applied. 3 If two different objects are under the influence of equal forces, they will have equal accelerations. 4 The net force acting on an object that maintains a constant velocity is zero. 5 The net force acting on an object that remains at rest is zero. 6 If a net force acts on an object, the object's velocity will change. Review Newton's First and Second Laws and the definition of acceleration.
8 more posts in this thread. [Missing image file: cauchy.png]
Confused about contour integration. I'm trying to integrate (x - sinx)/x^3 along the real axis. Should get pi/2. Confusing me for two reasons. Firstly... the normal thing to do would be to consider the imaginary part of z + e^iz / z^3, where the contour goes along the real axis, dodging z = 0 with a semicircular arc, and then round the upper half plane in a big semicircle. But when I take the limit of the little semicircle, I get something like pi/r^2, which is unbounded as r goes to 0. Also... I note that the integrand has a removable singularity at z = 0. So why can't I just like... remove the singularity. Then I've got an everywhere-analytic function... but then if I integrate along the real line and along a semicircle in the upper half plane, I should get 0, which is wrong. >:|
3 more posts in this thread. [Missing image file: 1337279586255.jpg]
Arbitrage betting; Now I know that if something seems too good to be true it is, and that there's no such thing as free money. This said, I don't understand why arbitrage betting wouldn't work? I've tried to do a bit of research but everything I come across is biased propaganda in favour of arbitrage betting company's. Now I've hit a wall due to my personal mathematical abilities so I thought I'd come here and ask you guys how it works/why it won't work
11 more posts in this thread. [Missing image file: Die.jpg]
Probability is a flawed science because it requires random numbers. If I roll a six sided die and get a six, the probability of that happening is not 1/6 it is 100 percent as proven by me having rolled that and nothing else. Given a controlled environment there can be no significant deviation from the known laws of physics effecting something like a dice roll. discuss
0 more posts in this thread. [Missing image file: 1319223044668.jpg]
I'm a third year undergrad studying Biochem and looking for some good, recent documentaries on biology (preferably molecular or neruo-) or chemistry (preferably organic). Any suggestions, /sci/? I've been making my way through the netflix documentaries and they're grossly simple and disappointing. Or other great documentaries would also be appreciated.
6 more posts in this thread. [Missing image file: 1A50DE29-77E3-4AA5-8E8C-81250D26C838.jpg]
Could some one explain in simple terms, what quantum excitation, and metastability are?
5 more posts in this thread. [Missing image file: gi.gif]
how do I \int_{0}^{2\pi} \sqrt{a^2sin^2(t) + b^2cos^2(t)} dt

pic unrelated

5 more posts in this thread. [Missing image file: super cool dudes.jpg]
So if you use the newtonian gravity equation, during a solar eclipse, where the moon is directly between the earth and the sun, the gravitational force on the moon by the sun is about twice as great as earth's on the moon, at the same time the moon's velocity is basically tangential to its orbit around earth, so it's not like it's moving towards earth which could serve to work in earth's "favour". A simple inspection would lead you to the conclusion the moon should start to orbit the sun, but why does it not? Seriously im a pleb, and dont know. Is it that if you account for earth's velocity with respect to the sun, or something, I really dont know, please respond
18 more posts in this thread. [Missing image file: cat.jpg]
Hey /sci/, how do you wind down from all of that thinking? I'm getting tons of headaches and I'm having trouble sleeping
16 more posts in this thread. [Missing image file: 1324186678112.jpg]
>not putting your axiom of choice in the fridge






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