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Comments:
<0> is there good physics software for linux ?
<1> anubiss: python? What kind of physics?
<1> I haven't looked too much into software that can do graphical models of spring systems. You could do the graphics with gtk, and the springs themselves are pretty simple discrete math.
<2> in the fantastic four, where does the energy come from for the flaming torch guy?
<2> shouldn't he be loosing m*** as it burns?
<2> or can you have a fire without using m***?
<2> hmm
<2> in the film they said that it's possible to ignite the earth's atmosphere
<2> is that true?
<3> fire doen't use m***
<3> conservation of m*** applies
<3> and why are you taking some comic book seriously?
<2> it's the film :P
<3> go watch some CSI, they explain it all there
<2> sure there's conservation of m*** (***ume no m*** is converted to energy(
<2> but when something burns, it releases m***
<3> no m*** is converted to energy with a normal fire
<2> hmm
<2> don't you have to have g***es etc released
<3> I guess it depends on how you stretch the definition of fire
<2> in what way?
<3> there doesn't have to be a net change in pressure, I don't think
<3> if you combust stociometric hydrogen and oxygen in a container then let it cool, the pressure should be lower in the end I think
<2> hmm
<3> after it cools
<2> what's stociometric?
<2> if you combust them, then what are you left with exactly?
<3> no excess reagents
<3> water
<3> 4H + O2 = 2H2O
<2> ..
<2> if you set fire to hydrogen and oxygen, you'll get water?
<3> yes
<3> well, water vapor at first
<2> that sounds nuts :-)
<3> but if you let it cool without escaping it'll be water
<2> hmm
<2> the energy released as heat and light is the difference in energy, right?
<2> between 4H+O2 and 2H20
<2> between 4H+O2 and 2H2O
<3> yes the reaction is exothermic
<2> if you just mix hydrogen and oxygen, would anything happen?
<2> does it need a spark?
<2> or will they just combine?
<3> it needs a spark if you want it to happen all at once, I'm not sure if it'll happen spontaneously if you let it sit long enough
<3> I don't think it will
<3> I'm no chemist, you'll have to ask someone else why it requires that initial energy to start the reaction
<2> if you get them to react, they give off heat (hence exothermic)
<3> probably to break some bonds on the O2 or something
<2> is it just a naming thing about whether the heat is fire or not
<2> if it's hot enough, then it gives of visible light
<3> yes
<2> is there any particularly difference between something being hot, and something being on fire
<2> i'm guessing there must be since my oven gets hot, but clearly isn't on fire
<3> if it's not oxidizing I don't think you can say it's on fire
<3> a light bulb filament isn't really on fire
<2> when I burn a match, it gives off visible light.. yet it's probably cooler than my oven, right?
<2> hmm
<3> the match flame is probably around 1800F
<3> your heating elements in your oven are probably more like 1100F
<3> judging from color
<0> synx: mecanics, first year physics
<2> hmmmmmmmm
<2> Gigs: the match is at 1800F ?
<3> you can't always judge from color because some things can color a flame
<3> no the hottest part of the flame is probably at least that
<2> hmm
<2> i don't think a match is acting like a black body radiation though is it? (***uming you're getting the temperature from that)
<3> you are right, the compounds burning in the match color the flame more than blackbody color
<3> my match temperature estimate is just based off various guesses
<3> not as much the color
<2> fire is to strange
<3> well one thing it is not generally is plasma
<3> there's a common misconception that flame is plasma
<4> lightening travels through plasma?
<3> yes
<4> if you ionize air, does that alone make it plasma, or it has to be charged up a lot?
<3> the electrons have to be free
<3> so yeah, if it's fully ionized
<2> isn't that what ionizing it means?
<3> yeah
<2> hmm
<4> is it possible to have cold ionized air?
<3> yeah
<4> I was under the impression that plasma had to be high-energy
<4> relative to the other phases
<2> so you could have a cold plasma?
<3> I believe the plasma leaders that lightning goes through aren't hot until the current goes through them
<4> so all you need is a huge potential difference
<2> actually heat would lower the point at which the electrons are free
<3> that's one way yeah
<3> I don't think so john
<2> hmm or not
<3> electrical current sustains a plasma channel arc
<2> Gigs: yeah that was rubbish i think ;-)
<3> if you have enough current you can sustain a very long arc even at low voltage
<3> just have to initiate it as a short arc and draw it out hehe
<2> Gigs: but i guess the resistance would heat the air
<3> so I think the heat sustains the plasma channel
<2> Gigs: where it arcs, is that a plasma?
<4> the more excited the electrons, the less the binding energy is I ***ume
<2> i.e. a cold plasma?
<3> it arcs within a channel of plasma
<4> more current = hotter = more excited electrons
<3> the initial corona is within a cloud of cold ionized air
<3> so I guess that's cold plasma
<5> D[ArcSin[1/x],x]
<5> % D[ArcSin[1/x],x]
<6> Manyfold: -(1/(Sqrt[1 - x^(-2)]*x^2))
<1> I've heard the term "useful energy" before, but I'm not clear on the concept. What's the difference between energy in the form of heat and energy in the form of gasoline or in other chemical bonds? Is "useful energy" not energy at all, but instead a way of describing some abstract entropy reduction stuff?
<5> usefull energy is energy that could be used to do work
<1> define "used"
<1> and "could"
<1> I really don't understand this stuff...
<7> synx: Hey there.
<7> synx: It turns out that some energy is more easily accessible,
<1> hey
<7> let's talk about it in terms of food
<7> say that you have a source of nutrients in your kitchen
<7> versus the same amount of nutrients in the store down the street
<7> it takes less energy to get to your kitchen
<7> or at least, if you've cleaned the dishes ;)
<7> that's basically the idea
<7> heh'
<1> Yes I understand. But what does "accessible" mean, in scientific terms?
<7> There are no exact mathematical terms, it is indeed vague and you really just have to use "judgment" so to speak (experimental evidence always handy!)
<7> Hmm..
<7> let's get a quote
<1> You can't use energy, because it never decreases. It just converts to different forms. So that means energy can't be "useful." What's useful is work.
<1> So... should we talk about useful work?
<7> Ah, that's more easy to talk of (I can do this, hurray)
<7> Yeah, that's actually getting into some philosophy (so to speak)
<1> But work only happens when something's moving...
<7> because you have to define what is useful
<7> nah, ignore work for the moment
<7> there are very little definitions of what "useful" is
<1> Well, anything that can light a light bulb I think is useful.
<1> Through some mechanism.
<7> Right, that's useful - to you - so that you can see your work.
<7> And somebody may think a church is useful, while others may disagree
<7> so you get some nonsense relativism in there
<7> and you really really have to be careful with the word 'useful'
<8> i think what you guys are talking about is gibbs free energy
<7> I doubt that synx is talking about anything so specific
<7> I may be wrong
<7> in that case ignore my tangental thoughts :)
<1> Falling sand bag? Attach a pully, turn a generator, light a bulb. It's useful. Dynamite? Set it off in a chamber that pushes a piston up that turns a generator, light a bulb. It's useful. Ashes? well they're really not that useful.
<7> It's useful? Can you prove that? hehe
<1> Hotwire: Is it really gibbs free energy? Not sure about that...
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