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Topic: A physics question . . .

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  1. #1

    A physics question . . .

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    Just curious . . .

    There is a lot of space between the electrons in an atom and the atom's nucleus. So much so, that an atom is mostly empty space. Which means the objects they create are mostly empty space. Which means the world is very much an illusion, as many objects seem so solid.

    So my question is . . . what makes light bounce off of an object?

    Obviously is doesn't bounce off of all objects, it can go through many, like air, glass, water, and some plastics. What is it about the atomic make up of an object that allows or doesn't allow the light in our visible spectrum to pass?

    Sean Patrick Hannifin
    My MP3s | My Melody Generator | my album
    "serious music" ... as if the rest of us are just kidding

  2. #2

    Re: A physics question . . .

    God.



    No seiously,

    The relative amount of atoms within a given space or density and the relative quality known as the different states of matter. Matter just being different kinds of "frozen" energy. Or in other words energy in slower states of motion.

    The universe is a universe of different states of motion. This appears first in the Vedic Hymns I believe.

    Read that book by that wheelchair riden guy. Forgot his name. Sorry. He actually came up with some mathmatical proof of that which the Vedics have sung about for thousands of years.

    Jose

  3. #3

    Re: A physics question . . .

    My understanding is this for items that reflect light:

    1) A photon hits an atom or molecule.
    2) The photon "excites an electron", moving it up to a higher energy band. The electron has stored the energy of the photon.
    3) When the electron relaxes back to its initial position, it releases the energy in the form of another photon.
    4) That photon hits your retina, and you see that item as red, blue or green, depending on the frequency of the photon. When lots of photons hit the retina with a wide band of frequencies, red, green and blue are all detected, and perceived as white.

    For items that don't reflect light:

    1) A photon hits an atom or molecule.
    2) The atom or molecule soaks up the energy of the photon as increased heat, but it does not excite an electron or give off a photon.
    3) Since no photons hit your retina from this material, you perceive it to be black.

    Phosphorescent materials are able to hold their electrons in the higher energy state for some period of time. They essentially store light. As the electrons slowly relax into the lower energy state, they give off photons, and you see the plastic skull glow in the dark.

    At least, that's what I remember from school...

    -JF

  4. #4

    Re: A physics question . . .

    Thanks! That makes some sense . . . but . . .

    If matter is mostly empty space, what makes a photon hit an atom in the first place? And does it make a difference whether it hits a neutron, photon or an electron? Do photons hit atoms when they go through glass just because there are so many atoms, and the chances of it not hitting an atom are very slim? Yet why can neutrinos pass through so many atoms so easily? Why does the light travel in a straight line when it goes through objects? (refraction only happens when the speed of light changes because of the matter it's traveling through, e.g. water to air)

    And what about reflections?

    More questions just keep coming! Too bad they don't teach this stuff in Phys 160 . . .
    Sean Patrick Hannifin
    My MP3s | My Melody Generator | my album
    "serious music" ... as if the rest of us are just kidding

  5. #5

    Re: A physics question . . .

    First of all... We picture the atomic world as being made up of physical particles and space so we can get our heads around it. But these are only models that help us to understand things. It would be like using rocks to describe a computer to a caveman.

    But to continue with the model...

    Keep in mind that electrons spin around the atom at a miraculous rate. Imagine them going so quickly that they build a shell around the nucleus. So the photon hits this shell, and may make the shell expand to the next energy level.

    Also, be aware that light acts like both a particle and a wave. There are some experiments that show photons acting as discrete particles, and others that show photons acting as waves. It might be easier to picture light as energy waves in this instance. As the energy wave gets close to the electron shell, they interact. The light acts more like a blanket than a particle in that mental model.

    Reflection is like bouncing a cue ball off of a pool table's bumper - the light bounces off the material coincidently. This requires a material that can be formed into a smooth, flat surface that reflects all frequencies evenly. As you distort the surface, you get a circus clown effect. As you distort the surface at the micro-level, you get blurring. If the micro-surface is uneven enough, you get a non-reflective surface that reflects light every which way.

    Here's a real mind twister. Imagine a pinball in a photograph. The only thing you see on it is a spherical reflection. So, essentially, all of the light coming from it is simply a re-mapping of the light from it's environment. Put it in a green space and the pinball is green. In a blue space it's blue. In a forest it's brown on the bottom, green in the middle and blue/white on top.

    So, when you look at this photograph of a pinball, how does the human mind instantly recognize it as spherical? How can we perceive the shape of a chrome bumper? And how would one program a computer program or robot to recognize the material as chrome and spherical, rather than just round and semi-random?

    Interesting stuff!

    -JF

  6. #6

    Re: A physics question . . .

    Thanks Jon,

    I had forgotten about the agitation within agitation thing. Pretty cool.

  7. #7

    Re: A physics question . . .

    Thanks for the response!

    Quote Originally Posted by JonFairhurst
    Here's a real mind twister. Imagine a pinball in a photograph. The only thing you see on it is a spherical reflection. So, essentially, all of the light coming from it is simply a re-mapping of the light from it's environment. Put it in a green space and the pinball is green. In a blue space it's blue. In a forest it's brown on the bottom, green in the middle and blue/white on top.

    So, when you look at this photograph of a pinball, how does the human mind instantly recognize it as spherical? How can we perceive the shape of a chrome bumper? And how would one program a computer program or robot to recognize the material as chrome and spherical, rather than just round and semi-random?
    That is weird . . . I never thought about that! Headache . . .

    I'm still trying to get through this short little book Einstein wrote called "Relativity" . . . my mind hurts . . .
    Sean Patrick Hannifin
    My MP3s | My Melody Generator | my album
    "serious music" ... as if the rest of us are just kidding

  8. #8

    Re: A physics question . . .

    Specific or general? It's all relative.

    -JF

  9. #9

    Re: A physics question . . .

    Quote Originally Posted by JonFairhurst
    Specific or general? It's all relative.

    -JF
    Both special and general . . . though I don't quite understand the difference yet . . .
    Sean Patrick Hannifin
    My MP3s | My Melody Generator | my album
    "serious music" ... as if the rest of us are just kidding

  10. #10

    Re: A physics question . . .

    Quote Originally Posted by JonFairhurst
    First of all... We picture the atomic world as being made up of physical particles and space so we can get our heads around it. But these are only models that help us to understand things. It would be like using rocks to describe a computer to a caveman.

    But to continue with the model...

    Keep in mind that electrons spin around the atom at a miraculous rate. Imagine them going so quickly that they build a shell around the nucleus. So the photon hits this shell, and may make the shell expand to the next energy level.

    Also, be aware that light acts like both a particle and a wave. ...Blah..blah...blah...snore...snore...wha?

    -JF
    Jon,

    You haven't perchance seen the 'nerd' quiz over in the GPO forum have you. Pretty sure you'd ace it, hands down.

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