# lightburst

Senior Members

82

## Posts posted by lightburst

### Work along a curved path

I don't know what a Force per unit length is. I googled it and it seems to be related to electricity.

I already solved the problem using conservation of energy. The Work done by the wind was simply FD (Force times horizontal distance). I just prefer knowing a detailed solution is all so I wanted to do it in calculus.

I mean do I need to learn new math here? My experience is limited to single variable calculus. I mean I know how to do some of the more complicated stuff, but as far as being useful all I have is single var calc.

$F\int \cos\theta\; ds$

I tried to use the arc length equation s = r(theta), but the damn r is there when I want a D.

F/L * l(sin(theta) + sin(phi)) dl

I know that l(sin(theta) + sin(phi)) = D and you end up with (F/L)D dl and when you integrate you lose the L and end up with FD which is what I expect. I just don't know what F/L is.

### Work along a curved path

Generally, for a force F along a path P the work done by said force is $W = \int_{a}^b \! \vec F \cdot \frac{\partial \vec P}{\partial s}\, ds$, where s=a...b is a parameter describing the process along the path (e.g. time). Since the force is constant in this case, this simplifies to $W = \vec F \cdot \int_{a}^b \! \frac{\partial \vec P}{\partial s}\, ds = \vec F \cdot ( \vec P(b) - \vec P(a) )$.

Reason I am sketching this rather abstract calculation? Firstly, because it is what you asked in the headline. Secondly, because it demonstrates that the force of the wind in this case does not act on the vertical part of the path, only on the horizontal one. Also note that the force of wind in this example seems to be a conservative force.

Walk me through the math, please. I know the definition of Work along a curved path. I just don't know how I can apply it to this particular problem. My book isn't much help. (To be fair, this problem didn't even come from it)

I figure I need to represent the path as a function (or a vector function). I thought P = <R cost, R sint> but that went down the drain.

### Work along a curved path

I've been trying to compute for the Work done by the wind F using calculus. Haven't had progress at all.

### Definite Integration (Physics problem, sort of)

I don't see why it wouldn't be possible to use t as a bound on the v side. I mean the bound and variables within the equation aren't the same thing, right? The bounds are just some constants, no?

Also, they couldn't be the same end points because when you use, say the projectile motion/free fall equations, final velocity and time isn't the same and initial time = 0 and initial velocity isn't necessarily zero, no?

Of course v and t are connected by an equation as are dv and dt

hmm I guess it makes better sense if like the bounds of the left hand side is a function of t, as in v(t). Is there perhaps a proof/theorem/property/particular topic I could look up?

### Definite Integration (Physics problem, sort of)

You are given F(v) = -Cv2, the force as a function of velocity, and you need to show that x - x0 = (m/C) ln(v0/v) where m = mass and C is some constant.

My question is why and how does definite integration work when you have 2 variables?

I mean I was able to finish the problem using this as I've seen it be used in the textbook itself and also some math books, but I don't really understand or know how it works. In calculus classes, and also my book, definite integration is done using 1 variable. I mean we do multiple definite integrations but that's only 'on one side' and 'one at a time' and I've never really been taught definite integration on different variables on 'both sides' of the equation.

I feel like because the right side is being evaluated from 0 to t, the other side should be evaluated from 0 to t also.

### How to draw a circle without PI and how to obtain PI without knowing what a circle is...

Want to find out Pi? Physically measure the diameter and circumference of a circle and do (circumference/diameter). As you get more precise measurements, you'll see that you're seeing more decimal figures of the constant irrational number we all know as Pi.

### Atheism showing signs of religion. [Resolved-NO]

You assume that consciousness is something that is beyond 'brain mechanics'; that consciousness is not manufactured by the brain.

You can play with high-level interpretations of scientific laws all you want, but the fact remains. You first have to prove that we are more than chemistry. Alternatively, capture that ethereal consciousness right after a person dies and transplant it and see if it sticks. Or just capture one at all.

### Daedalus' Eighth Challenge

I'd like to see solutions, please. My try was a total failure.

I tried getting an equation of a parabola (y - h = A(x - a)^2) where A was in terms of the two points...

### Zombie Apocalypse !

*coughOnPiratebaycough*

Pretty sick movie. hah pun

### Time travelers caught on film.

Notice how the icons get smaller in the first vid. Plus, just square dots really.

Second vid is just bogus. Could be any device and the iPhone was never that thick or small.

I think this one of quite good though, but that's just me.

### Time travelers caught on film.

Time travel and we still think AT&T and GSM phones? Come on. It's like the 1800s talking about future transportation and saying "Where is your combustion chamber?".

### Time travelers caught on film.

Could simply be a mini-purse or a sunglasses case. I will call it odd when, some bench in a park, a person is sitting alone with a 'phone' on her ear with absolutely no reason to compel her to put her hands over her ears for a long period of time. Though given this scenario, it's still not absolutely definitive. Shady though.

Furthermore, she actually has the 'phone' quite lower than her ear. Somewhere in her jaw. Given the angle of the 'phone' at, say, 0:09, and the assumption that it is a straight device, rather than curved, the device only reaches the underside of her ear and clearly not ON her ear as though listening.

Anyone?

### At this day and age, what graphics card?

Sorry that is entirely not true, do NOT shop based on how high the model number and that actually is as bad of a performance benchmark than the RAM. NVidia GeForce 7900 performs much better than say GeForce 8600; burst doesn't know what the model number means, and bigger doesn't mean better (I mean they claim it here in Texas, but i digress).

Obviously. But surely a GTX 460 is better than a GTS 450, or an 8300 GS vs 8800 GT. Just out of the assumption that the company markets them as such. 'How much' better one is from the other is a different story and needs better research but in general that's how you would go.

I should have said 'per generation' and 'per company'. The logic doesn't also apply to AMD/ATI vs Nvidia because ATI has 'higher' model numbers for their gaming line of GPUs.

### Who the hell has laid these damn eggs?

possibly a turtle? As far as I have seen, snakes make some sort of nest for their eggs and it's not really underground.

### Mother's response on Facebook, to her son ''coming out''

Now we just have to get over the bigotry against facebook and its very 'active' userbase. Can't we just accept people the way they are, including their propensity to 'like' every single thing and to post about the most mundane crap?

You people make me sick.

### A game of Abstract Logic

I do agree that there are no 'tricks' to truly solve these kinds of puzzles, and kudos to those people who can solve these things in a snap. And I do agree that 'general purpose logic' is a lot more useful in practically any field than chess skills. But that does not in any way guarantee success in a given field.

It may be that there is a correlation between very good 'general purpose logic', which may be something that is in your mind, and in general 'being good at everything'. I mean it could be the case, who knows. But very good 'general purpose logic' does not in itself guarantee all those other things that compose intelligence and therefore does not guarantee success in any particular subject. You may have a better future in math though.

Certainly, not being very good at 'general purpose logic' does not also imply lacking all the other things that compose intelligence and therefore does not guarantee failure in any particular subject.

Of course, some logic ability is crucial but not the lightning fast conscious kind that these puzzles expect. I'm not sure who said this, but there is this education 'adage' around that goes something like a person that does slower arithmetic than you does not mean she is dumber. it could be that she has a deeper understanding and does it all manually where you instead memorized a table. Of course, the 'table' doesn't apply to this but the essence of it is part of what I'm saying.

People are complicated and you cannot assert that the lack of knack for these games means they are not so smart after all.

### A game of Abstract Logic

I don't see how whether some game has arbitrary rules or not relate to it being more 'for intelligent people'. I don't see how some game being more related to real life be more 'for intelligent people' either.

I'd say chess has more parallels to real life than logic games because life is more than just true or false. Variables change. Goals move. I mean you do use logical reasoning but a lot simpler because life is boring like that. The trick is to foresee the unforeseeable. Account for unknowns and predict possibilities. Rational thinking nonetheless, but not quite as polished and contrived as a logic game/test.

Chess may have arbitrary rules in the same way Hacky Sack does, but for every chess scenario there is such a thing as an ideal move. You either memorize the ideal move by memorizing the scenarios, or you look for it by thinking. Yea, some players cheat by memorizing but not everyone has savant long-term memorization.

It is still intelligence even if you're working under arbitrary rules. Chess, Physics (Nature), The Social Order, the Legal System.

You may be able to do these games 'out of the box', if one is endowed enough. But that doesn't create all what it means to be intelligent. The idea may be attractive because the ability is more inherent and you didn't have to learn anything beforehand but I say it's a matter of which framework fits best with your brain.

### A game of Abstract Logic

You are equating brilliant logic ability to intelligence. And implying that the ability to play great chess does not imply anything on intelligence. And that logic and chess have no relationship.

At this point we'd just be dancing on a head of a pin arguing what it means to be intelligent. But intelligence is also creativity, to see relationships, to rethink something to make it work, learning, to apply what is otherwise inapplicable and make it work. And some other subjective stuff.

I say being good at these kind of games is nothing but another personal knack. A knack that implies something about the person's intelligence, but is not the sole arbiter.

### A game of Abstract Logic

People are good at different things and think differently.

Einstein and Oppenheimer, for example, played against each other in chess and according to those who know more, I assume, about chess than I do, they don't even compete with the average grandmasters. Two otherwise possibly among the smartest people that ever existed sucked at a strategy game -- a game of the mind.

### At this day and age, what graphics card?

I'm pretty sure you won't have to worry about DirectX support in graphics cards of the past 5 years.

Video RAM is a marketing ploy. It is not even close to a good performance benchmark. The easiest way to shop for GPUs in terms of performance is really just by thinking 'higher model number, the better'. For Nvidia, 350/450/550... is the start of the more gaming oriented cards. For ATI/AMD, 3650/4650/5650... is the start.

These companies want you to think that higher Video RAM makes a better GPU, but it doesn't. It's like having a large pool with only a dinner table glass to fill it with.

Which companies have better GPU lines or competing models vary every year or so. That's when you go to review sites and see benchmark numbers.

Gaming GPU will be the biggest power consumer in a system. Better have the juice to give it, otherwise something might break.

### Is there an agenda behind psychology?

Who the hell cares where meditation started? Who the hell cares if only a minority of people did/do it? Who the hell cares if it's not 'western' enough? Who the hell cares if it's not western at all?

Would you deny yourself NZT-48 if it came from Japan instead of Pfizer? If it came out of a new field pioneered by Arabs?

### palm-sized spider, PL help

Climacophobia or bathmophobia are also possibilities. Maybe the spider was scary because he was by the stairs....

Seeing the photos above already gives me the creeps. I was thinking 'what if there was more of that thing...'. But honestly, stuff like black widows or those classes of smaller bugs don't really bother me. Although maybe when they are in enlarged photo form.

Its true though that I'm scared of heights. Only if I look down.

### palm-sized spider, PL help

I'm perfectly fine with small finger-tip size spiders, hell I even play with them, but anything larger freaks the shit out of me.

Saw this exact thing by the stairs just this week and almost fell to my death.

Does that count as arachnophobia?

### Is there an agenda behind psychology?

So what if it's not western? Half the electronics we use isn't exactly 'western' either. If it works, it works.

I believe you are mixing 'socially normal' and 'medically normal'. Although it's true that medical diagnosis does have some subjectivity to it, even more so in psychology, there is nothing 'normal' about a case where a person stops being functional (from 10 hours a day to a shut-in) because of the trauma of i.e. running over someone.

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