## Search found 95 matches

Sun Sep 16, 2012 11:52 pm UTC
Forum: Science
Topic: 2D laplace's equation (cartesian)
Replies: 3
Views: 1998

### Re: 2D laplace's equation (cartesian)

Right, I assumed as much. I guess my question is this: is it conceivably impossible to write down a closed form solution to a problem whose origin has been shifted, while a nice answer exists for the setup with the unshifted origin? If this is not the case, then I can only conclude that it is a bad ...
Sun Sep 16, 2012 11:22 pm UTC
Forum: Science
Topic: 2D laplace's equation (cartesian)
Replies: 3
Views: 1998

### 2D laplace's equation (cartesian)

Homework here: Rectangular pipe, infinite in the z direction. The sides in the y-z plane (at x=0 and x=a) are held at V=0, while the sides in the x-z plane (at y=0 and y=b) are held at V=V 0 I'm not assigned to find the form of V inside the pipe, just to explain why there cannot be a non-trivial sol...
Mon Sep 26, 2011 11:24 pm UTC
Forum: Science
Topic: what might this HW question be asking?
Replies: 2
Views: 1708

### what might this HW question be asking?

Asked to show that the mean-square charge radius of a uniformly charged sphere is <r^2>=(3/5)R^2. What exactly does this mean? Find the radius where Qenc = Qtot/sqrt(2)?

EDIT Well, obviously not 1/sqrt(2), since it isn't the rms, just mean square. So now no idea.
Thu May 26, 2011 11:08 pm UTC
Forum: Science
Topic: Could time be measured in meters?
Replies: 83
Views: 10863

### Re: Could time be measured in meters?

I don't see why the energy/distance thing is any different than the distance/time thing. Of course, I completely disagree - distance/time are NOT in the same units, which is why you have to throw in c somewhere, so if you take G and h/hbar to be fundamental constants, how are your results any differ...
Fri Mar 25, 2011 1:46 pm UTC
Forum: Science
Topic: Black Holes and Measurement
Replies: 9
Views: 1373

### Re: Black Holes and Measurement

Woops, didn't really verify the milky way mass, but still, that's a lot of mass.
Fri Mar 25, 2011 3:54 am UTC
Forum: Science
Topic: Black Holes and Measurement
Replies: 9
Views: 1373

### Re: Black Holes and Measurement

on a related note (maybe not, but I'm in relativity this semester), if you were looking at a black hole from the outside and considered the mass to be evenly distributed inside the event horizon (no singularity, just a big ball of mass), with density = density of air, the event horizon would be twic...
Wed Mar 23, 2011 10:00 pm UTC
Forum: Fit Club
Topic: In which Sarah becomes less fat...
Replies: 33
Views: 5785

### Re: In which Sarah becomes less fat...

If you're eating regularly (which I recommend, I think dieting is pretty fucking dumb, but don't listen to me), swimming/running will be plenty sufficient to stimulate muscle growth. I've never seen a female swimmer who wished she had more muscle. Neither have I. But then, neither have I ever seen ...
Tue Mar 22, 2011 2:10 pm UTC
Forum: Fit Club
Topic: In which Sarah becomes less fat...
Replies: 33
Views: 5785

### Re: In which Sarah becomes less fat...

Really, heavy aerobic exercise is the most efficient way to burn calories, so if you're going to be going to the gym, get on the eliptical, treadmill, or get in the pool! Strength training/situps/yoga is, in all honesty, a total waste of time if your only goal is to lose weight. The time you allot ...
Tue Mar 22, 2011 3:42 am UTC
Forum: Fit Club
Topic: Beginner's bodyweight workout/stretches
Replies: 9
Views: 2282

### Re: Beginner's bodyweight workout/stretches

Are you trying to bulk up a bit? If so, I strongly recommend Arnold's book: http://www.amazon.com/New-Encyclopedia-Modern-Bodybuilding-Updated/dp/0684857219 Really has all the info you could ever want, but if you are trying to get by without weights, go for pullups (you can reposition yourself in a ...
Tue Mar 22, 2011 3:37 am UTC
Forum: Fit Club
Topic: ams: getting fit
Replies: 72
Views: 17778

### Re: ams: getting fit

Really cool to see the graphs with consistent results, and it's awesome you're keeping up with it. If you want to strength train, hold off on using weights until you see some definition. IE, do pullups/pushups rather than lifting. Otherwise, you may have a tendency not to lose as much weight as you'...
Tue Mar 22, 2011 3:32 am UTC
Forum: Fit Club
Topic: In which Sarah becomes less fat...
Replies: 33
Views: 5785

### Re: In which Sarah becomes less fat...

Really, heavy aerobic exercise is the most efficient way to burn calories, so if you're going to be going to the gym, get on the eliptical, treadmill, or get in the pool! Strength training/situps/yoga is, in all honesty, a total waste of time if your only goal is to lose weight. The time you allot f...
Tue Mar 22, 2011 2:58 am UTC
Forum: Science
Topic: Variation of the dreaded airplane/conveyor belt...
Replies: 29
Views: 6395

### Re: Variation of the dreaded airplane/conveyor belt...

Think he means having propellers in front of the wings which actually push enough air over the wings to cause lift even when plane is not moving relative to air, which, I suppose, is possible, but you'd be a lot better off with vertical thrust if that's what you're trying to do.
Sun Mar 20, 2011 3:28 pm UTC
Forum: Science
Topic: Photon-photon gravitational attraction
Replies: 54
Views: 5036

### Re: Photon-photon gravitational attraction

thoughtfully wrote:I think a general approach here is to draw light-cones for the photons.

exactly, but from what doogly said, it seems like there's a small modification in GR.
Sat Mar 19, 2011 9:12 pm UTC
Forum: Science
Topic: Photon-photon gravitational attraction
Replies: 54
Views: 5036

### Re: Photon-photon gravitational attraction

How much relativity have you studied? While it is an interesting question, I feel like there are much, MUCH more interesting ideas without even leaving special relativity. By the way, if you assume gravity doesn't travel faster than c, then it follows the same rules for timelike/spacelike separation...
Sun Mar 13, 2011 4:27 am UTC
Forum: Science
Topic: The Science of Hot Air Blowers
Replies: 39
Views: 4729

### Re: Hand Dryers

At my school, we have high powered hand dryers that blow air really fast. It's been around for a few years, but it's different from the older models that just blow hot air. On the placard, it says that they are more efficient than the slower blowing models but I don't understand why. Why is faster ...
Fri Mar 11, 2011 3:25 pm UTC
Forum: Science
Topic: Anyone know where I can buy a solenoid?
Replies: 6
Views: 1541

### Re: Anyone know where I can buy a solenoid?

You'll have a problem with that if the coil is wrapped more than once (wouldn't be terrible, you'd just have to reconnect the lower layers to the upper ones).
Sun Feb 27, 2011 6:44 pm UTC
Forum: Science
Topic: Mission to an extra solar planet?
Replies: 6
Views: 1165

### Re: Mission to a extra solar planet?

Qaanol wrote:Actually this could be a great idea. See, you just have to bill the mission to an extrasolar planet as a mission, and then let all the fundamentalists from all religions be the missionaries.

I hope you're as happy as I am that I just found a sig.
Sun Feb 27, 2011 12:32 am UTC
Forum: Science
Topic: Mission to an extra solar planet?
Replies: 6
Views: 1165

### Re: Mission to a extra solar planet?

We were talking about this sort of thing in relativity a couple days ago. If you wanted to take a spaceship with a gamma of 10 (meaning your time flows 1/10th as fast, or the distance is 1/10th what it is in the rest frame, about .99498C), it would require that your final payload mass be .05 the mas...
Mon Feb 07, 2011 12:10 am UTC
Forum: Science
Topic: Is taking 8 grocery bags in 1 trip = 4 grocery bags in 2?
Replies: 20
Views: 2913

### Re: Is taking 8 grocery bags in 1 trip = 4 grocery bags in 2

hmm, good point. That may be due to some other effect, like liquid leaving and things crystallizing? No idea, I wouldn't be surprised if everything I think I know about that stuff is wrong.
Sun Feb 06, 2011 6:40 pm UTC
Forum: Science
Topic: Is taking 8 grocery bags in 1 trip = 4 grocery bags in 2?
Replies: 20
Views: 2913

### Re: Is taking 8 grocery bags in 1 trip = 4 grocery bags in 2

I've got so little knowledge when it comes to biology that I shouldn't even respond, but I will :D I think it's because the filaments aren't mechanically connected to the heads (meaning they slide), and when a greater force is pulling on them, they slip faster, meaning they have to cycle more freque...
Sun Feb 06, 2011 4:53 pm UTC
Forum: Science
Topic: Is taking 8 grocery bags in 1 trip = 4 grocery bags in 2?
Replies: 20
Views: 2913

### Re: Is taking 8 grocery bags in 1 trip = 4 grocery bags in 2

cause the force is proportional to the rate at which they cycle, since it's skeletal muscle and not smooth muscle.
at least, that's what I remember from anatomy, the only bio related class I've taken in college, so I'd be surprised if it were correct.
Sat Feb 05, 2011 5:06 pm UTC
Forum: Science
Topic: Is taking 8 grocery bags in 1 trip = 4 grocery bags in 2?
Replies: 20
Views: 2913

### Re: Is taking 8 grocery bags in 1 trip = 4 grocery bags in 2

Right, but the gain in time/distance needed at that higher efficiency will, for any reasonable situation, always overshadow the efficiency lost without using a lever (work divider/distributor). I suppose if you took it to the extreme of the strong man competition where they carry the car frames, the...
Sat Feb 05, 2011 4:54 am UTC
Forum: Science
Topic: Is taking 8 grocery bags in 1 trip = 4 grocery bags in 2?
Replies: 20
Views: 2913

### Re: Is taking 8 grocery bags in 1 trip = 4 grocery bags in 2

If energy efficiency is linear with respect to additional weight carried, then yes, 1 trip is more economical because you are eliminating the empty return trip. Unfortunately, efficiency isn't always linear. In most cases it get worse the heavier the load. For instance, carrying 10 additional pound...
Wed Feb 02, 2011 2:52 am UTC
Forum: Science
Topic: seasoning cast iron
Replies: 8
Views: 1864

### Re: seasoning cast iron

yup, that's the blog from which I got most my theoretical basis. That's weird, I could've sworn flaxseed was higher...

EDIT: Ah, it's because she mentions she used avocado oil, which is 500 some, and had just been talking about flaxseed (guess I mixed up the two).
Mon Jan 31, 2011 12:30 pm UTC
Forum: Science
Topic: seasoning cast iron
Replies: 8
Views: 1864

### Re: seasoning cast iron

Actually, flaxseed oil (drying) is what I had used originally (over this summer), and is the recommended one, but its smoke point is like 505, and I was only heating the oven to 500 (doesn't go any higher), so that was kind of a wash. Anyway, yeah, it could've just been the fact that the bacon oil w...
Mon Jan 31, 2011 3:04 am UTC
Forum: Science
Topic: seasoning cast iron
Replies: 8
Views: 1864

### seasoning cast iron

lots of bullshit, might be the most bs ridden topic on the interwebs. from what I gather theoretically, and from my own experience, you've got to get the oil above its smoke point in order for any "seasoning" to happen (otherwise, you just warmed up some oil in a pan, then wiped it out). I...
Mon Jan 31, 2011 2:39 am UTC
Forum: Science
Topic: Making lots of Hydrogen
Replies: 9
Views: 1652

### Re: Making lots of Hydrogen

Why not just make an engine (since you're extracting a combustible gas here and all)? Seems like there are much more efficient ways to gain back some energy from electrolysis (or use hydrogen for energy, regardless of how it is gathered).
Sun Jan 30, 2011 4:40 pm UTC
Forum: Science
Topic: A little energy question.
Replies: 12
Views: 1475

### Re: A little energy question.

Read A Brief (or Briefer) History of Time . I think the idea is that if "information" gets sucked in, the mass of the black hole goes up correspondingly (since information is going to be some organization of matter, or light, which will have some mass/energy associated with it) to maintain...
Sat Jan 29, 2011 8:05 pm UTC
Forum: Science
Topic: Being a Physics Major
Replies: 12
Views: 2844

### Re: Being a Physics Major

Best decision I ever made. If you'd rather do physics problems than write papers (who the fuck wouldn't), you can't go wrong. I don't know what it's like to not like physics, so this is just a guess, but you should probably only do it if you really do like it, cause there are a couple topics which w...
Mon Jan 24, 2011 2:50 am UTC
Forum: Science
Topic: Circuit Problem
Replies: 3
Views: 733

### Re: Circuit Problem

nevermind I just did it with a matrix, don't know why I can't add the equations nicely though.
Mon Jan 24, 2011 2:39 am UTC
Forum: Science
Topic: Circuit Problem
Replies: 3
Views: 733

### Re: Circuit Problem

I hope so, otherwise I'm retarded. I can't get a numerical solution for any of them.
Mon Jan 24, 2011 2:32 am UTC
Forum: Science
Topic: Circuit Problem
Replies: 3
Views: 733

### Circuit Problem

Cannot believe I can't do this (I'm a 3rd year physics major), but where the hell do you get the last equation for this circuit? You've got

I1 + I3 - I2 = 0
5 - (I1R1) - (I2R2) = 0
15 - (I3R3) - (I2R2) = 0
????
help plx
Thu Jan 20, 2011 12:45 am UTC
Forum: Science
Topic: Capacitors, AC and DC confusion
Replies: 11
Views: 3300

### Re: Capacitors, AC and DC confusion

holy moly it's wbeaty! off topic, but I was trying to find that discussion about an electrostatic magnet which was mentioned on this site (pointing to your site), but couldn't find it. where it be?
Sun Jan 16, 2011 1:14 am UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2910
Views: 684290

### Re: RELATIVITY QUESTIONS! (and other common queries)

Very dense string, not quite dense enough to collapse (very strong too, and perfectly straight). Get it close to c (along the long axis), and to another frame, as its length contracts, it becomes more dense, eh?
Sat Jan 15, 2011 6:40 am UTC
Forum: School
Topic: Thoughts on math homework in college
Replies: 27
Views: 4882

### Re: Thoughts on math homework in college

Calc 3 professor I had last semester did it best, imo. We don't get a homework grade. Instead, it's used as extra credit: Out of a set of 15-20 problems, he picks 2 or 3 to be graded (each worth one point), and, at the end of the semester, every 3 points adds a percentage to our total grade. Ended u...
Fri Jan 14, 2011 3:05 pm UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2910
Views: 684290

### Re: RELATIVITY QUESTIONS! (and other common queries)

on the topic of special relativity: any significance to a negative s^2? (spacetime interval) I know it's arbitrary as to whether you assign timelike or spacelike to be negative, but is there any significance at all that s can be imaginary?
Fri Jan 14, 2011 12:25 am UTC
Forum: Science
Topic: Liquid Rails on a Railgun
Replies: 8
Views: 2035

### Re: Liquid Rails on a Railgun

What if you had the two rails parallel, and the projectile secured above the two rails by walls on either side and a ceiling. Then, above each rail, a hole in the projectile (which is conductive-fluid-filled), so as to provide conductivity, without having the thing explode.
Mon Jan 10, 2011 8:46 am UTC
Forum: Science
Topic: public misconceptions
Replies: 1073
Views: 146337

### Re: public misconceptions

Re: the Sunshine scene. Edit: this reminds me of a recent Castle episode, where the murder victim suffered "explosive decompression" by being placed in a vacuum chamber. Correct me if I'm wrong, but I'm pretty sure there do not exist vacuum chambers that can evacuate air that quickly. Tha...
Sun Jan 09, 2011 6:49 pm UTC
Forum: Fictional Science
Topic: What fictional science is required for space-fighers?
Replies: 131
Views: 16729

### Re: What fictional science is required for space-fighers?

On the topic of inertial dampening: I don't know if this has been mentioned before, but if we were able to generate a sufficiently strong, uniform gravitational field, we could accelerate as fast as we want (there would be no limit to the g's humans could withstand, because we wouldn't feel them) - ...
Sat Jan 08, 2011 9:01 am UTC
Forum: Science
Topic: The end of the universe
Replies: 24
Views: 2205

### Re: The end of the universe

yeah, doesn't cosmological constant only overtake gravity at ~ the radius of the universe?