How fast does fire travel?

Discussion in 'Physics & Math' started by Stryder, Sep 26, 2002.

  1. chroot Crackpot killer Registered Senior Member

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    I've already answered this in considerable detail.

    - Warren
     
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  3. On Radioactive Waves lost in the continuum Registered Senior Member

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    chroot: is wind resistance not friction? wouldnt it be possible for evaporation due to increased heat from air friction?


    frencheneesz: i believe you were visualizing small water droplets that may have escaped liquid by means of vibration, when you said the "heavier vapor". but evaporating(vaporizing) means a vapor state (individual molecule not conected to another)
     
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  5. chroot Crackpot killer Registered Senior Member

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    What wind resistance are we talking about? I don't know how any of this friction stuff is relevant, but wind resistance certainly is a form of friction, and certainly does heat things up. That heat certainly can cause more evaporation. A perfectly smooth air-liquid interface, however, would provide zero cross-sectional area and thus zero friction.

    - Warren
     
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  7. On Radioactive Waves lost in the continuum Registered Senior Member

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    so if i get the jist of this discussion about friction and evaporation, you are saying yes its possible but the effect are negligable compared to the other causes of evaporation? beacuse somthing such as a raindrop would certainly encounter air resistance on its decent, likely causing some degree of evaporation.
     
  8. chroot Crackpot killer Registered Senior Member

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    Sure, if the air resistance heats it up, it'll evaporate faster. Do some calculations, let us know what the answer is.

    - Warren
     
  9. Frencheneesz Amazing Member Registered Senior Member

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    Chroot:

    You seem to imply that you know it, and others don't. I'll tell you I don't get that open-minded feeling from you.

    Hey this is me!: "you mentioned the vapor pressure and equalibrium of a liquid. Water has a layer of particles above it that are constantly condensing to water and then revaporizing to a gas. Why doesn't this vapor just fly off?"

    How bout I just leave my question like that and not give you any of my input on what I think, because you obviously don't care. I do care about what you think because you seem smart. Smart but bitchy. You must know that some vapor is more dense than other vapor, so what I was theorizing is that that vapor is more dense than the air above it, causing it to stay down at water level. Whats your plan?

    Oh, im sure you have at least heard of, more "energized" electrons and such. How can an electron be more energized? I can see a couple things: the electron travels faster, its quantum spin increases, it somehow gains more electromagnetic charge. I don't know much about quantum spin, so... An electron gaining charge sounds rediculous to me. So what is the variable for a more "energized" electron?

    "so is the increased evaporation similar to how an airplain flies? "

    I actually had that same thought a while back, I had to restrain myself.

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    "but evaporating(vaporizing) means a vapor state (individual molecule not conected to another)"

    By heavier vapor, i meant more dense vapor. Molecules are always interacting with eachother, no matter how small the interaction. Electromagnetism from mars is interacting with us, it is just too small to work against the relatively large interactions here. Vapor interacts with other particles just as much, it bumps into them a LOT.
     
  10. chroot Crackpot killer Registered Senior Member

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    First, I apparently do know it, and you apparently do not..

    Second, being open-minded and being oblivious to reality are two different states. Many things about the world around us are understood very well; evaporation is one of them. It's silly and stupid to talk about being "open-minded" to different explanations of evaporation. Man has done thousands, if not millions, of detailed experiments to study phase changes. Our current understanding explains the intimate details of every single experiment ever conducted. There is no room for open-mindedness: we understand the process.

    I am happily open-minded about areas of physics that aren't well understood.

    No, I don't care what you think. Neither do atoms of water.

    This is one of those things that beguiles all who first encounter subatomic physics. You're apt to thinking about the universe in terms of billiard balls and planets orbiting around stars -- in classical terms. Unfortunately, our experiments show us that the subatomic world just isn't that way. The particles don't have definite positions and momenta, they don't bounce off each other like billiard balls, and they generally just behave in ways that are hard to visualize. What most people don't realize is that there's no reason billiard balls should work as they do either; they just do. You take it for granted, because you've seen it every day of your life. Eventually, you'll come to recognize that the way electrons work is equally beautiful as the way billiard balls work.

    Spin has only a very small role in determining energy states in an atom. Charge also only plays a small role, that of shielding. In the first approximation, electrons can be thought of as existing within a "shell" surrounding the nucleus. The electron can actually be found anywhere in the atom, but it is far more likely to found in a thin spherical shell. The radius of that spherical shell corresponds to energy. Why? Because, as experiment indicate, it takes less energy input to knock electrons out of increasingly larger shells -- so those electrons are more energetic than electrons closer to the nucleus.

    I don't particularly understand what you're trying to convince me of here.

    - Warren
     
  11. Nasor Valued Senior Member

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    It has more potential energy because of its location around the nucleus. It has 'more energy' in the same way that an object some distance off the ground has 'more energy' because it could fall. You have to add energy (like, say, a photon's energy) to the electron to 'boost' it to a higher energy level in the same way that you would need to expend energy in order to lift an object off the ground. The big difference between an electron having energy because of its position about the nucleus and an object above the ground is that the electron can only have very specific amounts of energy, while an object could seem to have any amount.
     
  12. Frencheneesz Amazing Member Registered Senior Member

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    "It has 'more energy' in the same way that an object some distance off the ground has 'more energy' because it could fall."

    Yes i guess that is true. But when a rock, say, is up on a cliff, the cliff is holding the rock from falling, thus preserving its potential energy. What is holding the electron up? Why don't all the electrons just fall into the nucleus?

    Ok chroot, i am going to give an explanation based on my understanding. Don't just say i'm ignorant this time. The way I see it what is holding the electrons up is their speed, their orbit around the attractive nucleus grows as their speed increases. I'm sure you can agree that if electrons speed COULD flucutate, an increase in speed would mean an increase in orbit size.

    What is "THE" theory on why electrons stay up in orbit, and why some electrons have more energy and stay that way?
     
  13. chroot Crackpot killer Registered Senior Member

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    Frencheezy,

    Electrons around nuclei are not like planets around the Sun. Despite the fact that it seem elegant and simple that way, it just isn't that way.

    In fact, even your understanding of gravitational orbits is incorrect: orbital linear velocity decreases with increasing radius.

    You have to let go of your attempts to understand atoms the way you understand planetary systems. I know it's tough to let go of those kinds of concepts, but you will never be able to advance in the sciences unless you do. Experiments confirm over and over again that electrons can only have discrete energy states in an atom. We can then model the electron mathematically, such that our model agrees with experiment. Of course, the electrons don't have to solve equations, and our models are independent of the actual system. The fact that our model predicts discrete energies is not going to convince you that electrons have discrete energies, and it shouldn't -- but experiment should.

    Unfortunately, we don't have senses that can detect what happens at atomic scales. We can't "see" electrons, nor can we "watch" one move around a nucleus. Based on what our experiments tell us, the atomic world is very different from the macroscopic world -- so different that the concepts of "pictures," "images," "movies," and so on just don't apply. Nature is just radically different at atomic scales.

    The only way we can probe the atomic world is through experiments. We can bounce things off each other, and see how they rebound. We can heat things up, cool things down, pass electrical currents through things, and so on. It's the analog of a blind, deaf person trying to learn about a cat by poking it with a stick.

    The only "conceptual" way of thinking about the discrete energy states was given to us by Schroedinger. Since electrons (like all particles) act as either particles or as waves, depending upon the experiment, Schroedinger hypothesized that the electron can only orbit the nucleus in such a way that its wavelength fits into the circumference of the orbit. In other words, only those orbits which allow an integral number of wavelengths are allowed. In this way, the energy states are "resonances" with the intrinsic electron wavelength.

    To model this behavior, Schroedinger created an equation -- the Schroedinger wave equation -- which forms the heart of quantum mechanics. There are now several different formalisation of the mathematics of quantum mechanics, but most students learn the Schroedinger formulation first.

    It turns out that bound systems allow only discrete energies. A free electron, outside any potential well (like that created by a nucleus's electromagnetic attraction) can have any energy. Free particles do not have discretized energy states. However, as soon as the electron enters a potential well, the number of acceptable energies becomes discretized. This happens in many systems: semiconductors, for example, are a veritable playground of effects of discretized energy states, because the electrons in the conduction band (which don't actually belong to any single atom) are captive in a complex, three dimensional, periodic potential well.

    So, to your question, "why is it that way?" the only answer is "it just is." Think about billiard balls bouncing around a pool table. Is there any reason that the collisions should happen the way they do, with the angles and velocities we observe? No. They just do. We can model the collisions with math, and the math seems simple and beautiful and sensible. If billiard balls behaved differently, we'd have arrived at a different model, and probably still think the math was simple and beautiful and sensible. The world just is the way it is. No one will ever be able to explain why.

    Now the reason why some electrons in an atom have higher energies than others, and stay that way, is another postulate of quantum mechanics. (That's right, it's a postulate -- a concept that is assumed.) The postulate is that of Pauli's exclusion principle. The principle states that particles, like electrons, are fundamentally indistinguishable -- you can't label an electron, let it interact with an atom, and read the label later. Since fundamental particles are indistinguishable, there cannot be any two in exactly the same state. Once again, it seems the world simply works that way. Only one electron can exist with any given specific energy in an atom. It turns out that describing an electron's place in an atom requires four parameters -- four "quantum numbers." No two electrons in an atom can have the same four quantum numbers.

    I have the feeling some of this will unsettle you. It may ever spur you on to distrust physicists even more. All we do is perform experiments, examine the results, and develop models which agree with the results. A good theory is one that make lots of hard-edged predictions that can be verified experimentally. As soon as one experiment conflicts with a theory, the theory must be abandoned, in favor of a new theory which explains the new effect, as well. None of us physicists know why electrons do what they do any more than we know why billiard balls do what they do. We are but spectators set before the stage of reality.

    - Warren
     
    Last edited: Oct 10, 2002
  14. Frencheneesz Amazing Member Registered Senior Member

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    "orbital linear velocity decreases with increasing radius."

    I never said ANYTHING, about orbits of planets. I'm not even sure that planets do go slower in a higher orbit for planets..... I know that the time for one orbit is longer, but the path is longer too...

    If earth were to travel faster perpendicular to the sun, IT WOULD HAVE A FARTHER ORBIT, no questions asked. You can't contest this, its a fact.

    "You have to let go of your attempts to understand atoms the way you understand planetary systems. "

    You have the complete wrong idea. I am not going to "let something go" until it is disproven or something else makes more sense to me. I know that electrons, like any mass-having particle travels in straight lines unless effected by a force (electrons usually are), doesn't go the speed of light, and obeys the laws of phisics. All particles are like this, not only electrons.

    "Experiments confirm over and over again that electrons can only have discrete energy states in an atom. "

    Yes, Dr Seuss, those are called quanta. That does not prove anything. I said that electrons travel faster. The theory including quanta would predict that the increase of an electrons speed can only go up by a certain amount which defines the quanta. Im pretty sure you are confused by that...

    "the only answer is "it just is." Think about billiard balls bouncing around a pool table. Is there any reason that the collisions should happen the way they do?"

    Yes there is. It is pretty unscientific for you to say there is no reason. Obviously, the electromagnetic force is a large factor. I think I see where you are getting at: your saying why do things bounce at the same degree it hit at, the answer is it just is. I can see that and its true. We may find out one day why that is as well though.

    None of this unsettled me, I understand all this. Most of what you said doesn't disprove the idea that electrons can flucutate speeds.

    By the way, you didn't answer my questions, yet again, so here they are:

    What is "THE" theory on why electrons stay up in orbit, and why some electrons have more energy and stay that way?

    I have never come up to a particle problem (this excludes light) that I couldn't come up with an explanation to using only the electromagnetic force and gravity. The two nuclear forces, I confess, I don't know much about, but i haven't seen a problem dealing with them yet, need to find those....
     
  15. chroot Crackpot killer Registered Senior Member

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    Frencheezy,

    First, let me make a deal with you: you start getting hostile with me, and I'll just revent to calling you an idiot (which you are). You are decidedly uneducated, yet you'd rather come up with your own theories before understanding existing theories. I've said it before, and I'll say it again:

    You have no hope of bettering a theory you don't yet understand.

    The linear velocity of a body in orbit decreases as radius increases. The exact equation is:

    v^2 = G * (m1+m2) * (2/r - 1/a)

    where v is linear velocity, G is Newton's gravitational constant, m1 and m2 are the masses of the two bodies, r is the distance between the two bodies, and a is the semimajor axis of the orbit.

    This leads directly to Kepler's third law of orbital motion.

    This form is shown in full derivation in many sources from first priciples (Newton's law of universal gravitation).

    Too bad, cheeseball, you're wrong. Orbits with higher radii have lower linear velocities.

    No, they aren't. The term 'quantum' refers to a 'packet' of radiation, not a unit of energy in an atom.

    Was that a double-take, or what?

    I wasn't trying to disprove your theory. I was trying to describe the accepted theory. You asked rather specifically what the theory was that discretized atomic energy levels.

    I answered this in detail, as well -- it's called the Pauli exclusion principle.

    Since you're accepting challenges: Explain the beta decay of a free neutron. Show me how your model directly and explicitly is capable of calculating the following quantities:

    1) The observed mean lifetime of free neutrons.
    2) The observed energy distribution of the electrons produced in the decay.

    Since you want me to disprove your stupid little "electrons move faster when temperature is increased" theory, here's the evidence:

    Take a pure substance, say, hydrogen. Cool it down in whatever way you'd like. Observe the Balmer series, produced by electrons falling into the n=2 shell. Observe the frequencies. Write them down in a column.

    Heat the hydrogen up, as much as you'd like so long as it doesn't ionize. Observe the Balmer series, produced by the electrons falling into the n=2 shell. Observe the frequencies. Write them down in a column.

    Compare the two columns.

    - Warren
     
    Last edited: Oct 10, 2002
  16. On Radioactive Waves lost in the continuum Registered Senior Member

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    french: i beleive it was explained to me that the electrons are held in orbit by a combination of attractive/repulsive forces

    yes you do need to learn about the nuclear forces, since just about everything we experience is a product of the electro-static force. (as far as i know)



    "Too bad, cheeseball, you're wrong. Orbits with higher radii have lower linear velocities"


    do you mean on average? isn't the velocity dependent on it's distance from the sun? in which case, there could be a circumstance where a planet with a larger orbit at perihelion will travel faster than the planet with a smaller orbit at aphelion.
     
  17. chroot Crackpot killer Registered Senior Member

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    This is very true. I was really talking about simple circular orbits (although I didn't say it). In the case of simple circular orbits, linear velocity always decreases as radius increases.

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    - Warren
     
  18. Frencheneesz Amazing Member Registered Senior Member

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    "you'd rather come up with your own theories before understanding existing theories. "

    Although you may not believe me, I do understand current theories. I just have a different picture only for the reason that IT MAKES MORE SENSE TO ME.

    "The linear velocity of a body in orbit decreases as radius increases."

    I guess if a higher orbiting planet were to have a higher speed, it would just fly right off...

    I do know that if you increase the linear speed of a planet it will not go into a lower orbit. I am right, right?

    "The term 'quantum' refers to a 'packet' of radiation"

    They are called quantum energy states. And they have a lot to do with radiation. If you don't believe me this site refers to it http://hyperphysics.phy-astr.gsu.edu/hbase/mod5.html

    "Was that a double-take, or what? "

    I mean that there is a reason, but we might not have found it yet.

    "Explain the beta decay of a free neutron. Show me how your model directly and explicitly is capable of calculating the following quantities"

    Yeah... There it is. I'm pretty sure that has to do with the Strong and weak nuclear forces. Like I said I don't know much about them. Do you want to tell me what particles -emit- (for lack of a better word) the strong and weak nuclear forces?

    I never said I had math for my little idea. I know that all the math we have right now is more or less correct (a bit more correct than newton but probably not perfect). I just think that the reasons the math works is different than the way you think it is.

    "Compare the two columns. "

    I know for a fact that particles at different heat levels emit slightly different radioactive frequencies. That is a fact. It also helps my idea.... Quite nice.

    On Radioactive Waves -

    "i beleive it was explained to me that the electrons are held in orbit by a combination of attractive/repulsive forces."

    Ya, most are. But in something like a normal hydrogen atom. There is no repulsive force comeing from another electron, because there is no other electron.

    Im wondering what could be making that hydrogen electron stay in orbit instead of crashing down into the proton. ...

    "yes you do need to learn about the nuclear forces, since just about everything we experience is a product of the electro-static force. "

    The electro static force (aka electromagnetic force) is not a nuclear force. There is the weak nuclear force, strong nuclear force, electromagnet force, and gravity. The two nuclear forces are the only ones called, understandably, the nuclear forces.
     
  19. chroot Crackpot killer Registered Senior Member

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    2,350
    Frencheezy,

    You obviously don't. Sorry.

    Duh, kiddo. I'm an astrophysicist. You said 'quanta,' not 'quantum.' The term 'quanta,' as established by Planck, referred to packets of radiation.

    The W and Z bosons are the carriers of the weak force, while the gluon is the carrier of the strong force. Quarks feel both forces.

    There's no such thing as a "perspective" on how math works.

    This is false. We're not talking about radioactivity, we're talking about electromagnetic emission. And you're wrong, the frequencies are the same, no matter what the temperature. Either perform an experiment, or look up the results of one. You don't gain points in this game by denying the experimental truth.

    This is false.

    French, how long do you intend to deny the experimental reality around you?

    - Warren
     
  20. On Radioactive Waves lost in the continuum Registered Senior Member

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    985
    "i beleive it was explained to me that the electrons are held in orbit by a combination of attractive/repulsive forces"

    i havnt taken quantum physics yet (in fact i havnt even passed mechanics but i was in it for a while) so excuse me if this is way off, i am quoting somthing that was explained to me when i was three or four years old

    [edit] oops i remember now. its the protons and neutrons that repel each other until the connect, then they are strongly conected. please excuse my ignorance, as all the quantum physics/mechanics i know is from my own interest. when my math skill is sufficient enough i will take actual classes... until then- i will get through calculus[edit]

    "yes you do need to learn about the nuclear forces, since just about everything we experience is a product of the electro-static force"

    i am aware the electro static forces is its own force and not a nuclear force. i made this statement with the implication that since we dont experience the nuclear force it is not intuitve as to how it works from an everyday observation ( although you could observe the every in detail until your eyesight is gone).

    the electrostatic is understood in our concious, from experiments conducted by our subconcious. I dont see how we experience nuclear forces in such a way that our bodies can run "experiments" to grasp their intricate workings such as we are able to do with the electrostatic force.
     
    Last edited: Oct 11, 2002
  21. On Radioactive Waves lost in the continuum Registered Senior Member

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    985
    a question for warren

    warren:

    how would you describe the movement of an oil sllick across the surface of water when blown upon? friction? or some type of resonating wave on the water surface / combination of both?

    i am wondering since you said the smooth surface of the water limits the interactions possible with the air

    also, could you give me an explanation of what a tachyon is? i read in my physics book that they are theorised to be capable of travelling back in time, though my book is likely outdated . i've yet to come across a good explanation of what tachyons are, but they are smaller than quarks right?
     
  22. chroot Crackpot killer Registered Senior Member

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    2,350
    On Rad Waves,

    Certainly, if you blow on the surface of the oil slick, you're going to push it around. The dominant theory on how moving air gets a "grip" on a smooth liquid surface involves microscopic "capillary waves" that are always present on a liquid surface. These capillary waves provide a bit of wind resistance, and rapidly build up into larger waves. These waves are then capable of moving particles in the surface around. Note that this movement doesn't affect evaporation, which depends upon particles escaping the surface, not being pushed around within it. The thermal velocities of individual water particles in the liquid is very high -- blowing on the surface produces a net "drift" in the direction of the wind, but doesn't substantially affect the velocities of the particles.

    Tachyons do not exist. They are hypothetical, science-fiction type particles. Since normal matter particles cannot ever go the speed of light, but only approach it asymptotically, some have theorized that there are "mirror" particles that can only go faster than light, and can only slow down to light speed asymptotically. There is, at the time, no experimental evidence whatsoever of the existence of anything like tachyons.

    By the way, the concept of a particle's "size" is a difficult one. Fundamental particles (leptons and quarks) do not appear to have any size at all. As best we can tell experimentally, they behave like geometric points. Particles made up of these fundamentals -- protons, atoms, etc. -- do appear to have a definite size, since the point-like fundamental particles within move around each other in something like "orbits." The intra-particle distance, then, appears as the particle's "size."

    - Warren
     
  23. Frencheneesz Amazing Member Registered Senior Member

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    739
    Chroot:

    When I say I understand the current theories, I don't mean I have mastered everything. I just mean I see how they are thinking. I am not regurgetating those theories, I am trying to come up with my own way of thinking about it.

    "You said 'quanta,' not 'quantum."

    I suppose you haven't ever taken Latin? Quanta is the plural of quantum. You know like QUANTity, it just means a unit.

    "The W and Z bosons are the carriers of the weak force, while the gluon is the carrier of the strong force. Quarks feel both forces. "

    Ok, would it be too much trouble for me to ask you what particles are interacted with these forces by how much? Like electrons and protons have -1 and +1 charge respectively, What particles have what nuclear attractions? You said quarks feel both forces, but do all quarks "feel" the force by the same amount?

    "And you're wrong, the frequencies are the same, no matter what the temperature. Either perform an experiment, or look up the results of one."

    Nie, stupid dopplar effect confused me.

    --"i beleive it was explained to me that the electrons are held in orbit by a combination of attractive/repulsive forces"--

    "This is false"

    Huh? Isn't everything "held" in whatever path they are in because of forces... What else could it be?

    Ok chroot, Lets just say I agree with you. Since you say orbits of planets decrease in speed as they go farther out, does the same hold for electrons? And why can't electons change speed (sorry its contradictory to the last question)?

    "By the way, the concept of a particle's "size" is a difficult one."

    As I see it, Size of a particles has to do with the forces it is creating, like the size of an electron can't be said to be smaller than its electromagnetic field, right?
     

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