Why is infrared "heat"?



  •  Hmm, have odd sort-of technical, but poorly formed question... AH! ask smart people at TDWTF!

    ------

     My boy, aged barely 5, was asking about warm (red,orange) and cool (green,blue) colors.

    He noted that it was strange that blue is a cool color, but that blue flame on the stove is the hottest.

    Got me to thinking. Why do we experience infrared light as "heat"?  Is it sensory or a peculiarity of the ratio
    wavelength to molecule-size or somesuch i.e. something physical?

    -------
    Question 2: SInce when do they teach Kindergardeners about primary/secondary and warm/cool colors?? 

     



  • Blue is a cool color and red is a warm color purely by association. Most of the blue stuff we see is cold or cool. Red/yellow glowing stuff is commonly hot. That's all.

    Hot glowing objects feel hot from a distance because there is the combined effect of the infrared radiation peak on top of plain heat transmission through air, though the heat from radiation is fairly minimal.

    Physically, however, blue light equals higher frequencies of eletromagnetic radiation. A blue flame is far hotter than a red or yellow one. If you make the flame even hotter, it disappears, because its emission shifts into ultraviolet, which we cannot detect.

    Some wikipedia stuff:

    Black Body

    Thermal radiation

     

    #2: I don't have kids and have no active connection to anyone under 18 or teachers. I have no idea what they're teaching the kids anymore. I don't remember learning about hot/cool colors until halfway preschool, though.

     



  • As the previous poster stated, it's a mixup of sorts. Red tends to be hot (red glowing stove, for example) while blue tends to be cold (ice has a blue shimmer to it, for example).

    Addionally, we can feel infrared due to its interaction with the upper layers of the skin. You can't feel ultraviolet light.

    The fun part then are the screen "temperatures" where "warm" equals a lower temperature than "cool". They may even give an actual temperature in Kelvin, based on the wavelength distribution curve for a black body at a certain temperature.



  • And I had a rather long edit to explain why we feel IR instead of UV, but the retarded "edit time limit" swallowed the text. Which reminds me, why is there no "LF/CR to <br />" conversion going on here?



    Anyway: Don't want to type it all again. IR and UV are of different frequencies and thus different energy quanta (E=h*ν). Each excitation mode of a molecule (be that directional, vibrational, rotational or electron) corresponds to a different energy amount/quantum.

    That energy quantum has to be met in a "all or nothing" approach - your photon doesn't have the energy corresponding to the energy level required? No interaction for you!

    Lastly, directional, vibrational and rotational excitation requires less energy than electron excitation.

    Which means, when coupled with kinetic gas theory, that only the kinetic excitations of a molecule play a role when looking at the temperature of, say, a solid like the skin.(<Ekin>=1/2kT, for every degree of freedom you add another 1/2. Which means that a molecule like CO2 (z being along the axis of the molecule) has 3 (x,y,z) + 2 (rotation around x and y) + 4 (vibration modes) = 9 degrees of freedom, which would result in<Ekin CO2>=9/2kT )



    UV usually only plays with the electrons, so no kinetic energy for you there! And thus no increase in temperature.



  • @Rhywden said:

    Which reminds me, why is there no "LF/CR to <br />" conversion going on here?
     

    Most likely because you're using something other than IE or Firefox. The Rich-text editor detection script of this forum is quite obsolete. Chrome users get a plain textarea which receives no formatting treatment at all save for bbcode.



  • @ijij said:

     My boy, aged barely 5, was asking about warm (red,orange) and cool (green,blue) colors.

    He noted that it was strange that blue is a cool color, but that blue flame on the stove is the hottest.

    And while we're in the neighborhood, why is green considered a "cool" color when any fool can tell you that green salsa is hotter than red.  And don't even get me started on wasabi.

    I'm 51 years old and still can't figure out why everyone calls a traffic light green when it's clearly white.



  • @ijij said:

    Question 2: SInce when do they teach Kindergardeners about primary/secondary and warm/cool colors??

    To quote the immortal Louis Armstrong: "I hear babies cry, I watch them grow. They'll learn so much more than I'll ever know."



  • @da Doctah said:

    I'm 51 years old and still can't figure out why everyone calls a traffic light green when it's clearly white.
     

    Because you're deuteranopic?

    But then, you would have said the same thing of green peppers.

    So I think you're referring to pedestrian lights, which are commonly red-white in the US, IINM— same as special bus lights here.

    That, or you're deliberately trying to confuse.

    Or you're attempting a projected joke, which didn't work out so well.

    Or you're high.

    On crack.



  • @da Doctah said:

    And while we're in the neighborhood, why is green considered a "cool" color
    Just because it makes things simple I think: Color wheel



  • @PJH said:

    Just because it makes things simple I think: Color wheel

    Bookmarked. Very cool.



  • @da Doctah said:

    I'm 51 years old and still can't figure out why everyone calls a traffic light green when it's clearly white.

     

    Because you're dyslexic?



  • @da Doctah said:

    I'm 51 years old and still can't figure out why everyone calls a traffic light green when it's clearly white.

    The bigger issue, and one significantly more important, is why so many people think Godzilla is green, when he's clearly been grey in every single (Toho) movie appearance. I mean, people don't generally color Frankenstein's monster with plaid, right? Why do they always make Godzilla green in cartoons?

    I demand a congressional investigation.

    @b-redeker said:

    Bookmarked. Very cool.

    See also this tool.



  • @blakeyrat said:

    @b-redeker said:
    Bookmarked. Very cool.
    See also this tool.

    Thanks, also very useful. But I especially liked the explanations that came with the first link, the color chooser only helps when you already know what you're doing (well, let's say it helps much more).



  • @blakeyrat said:

    See also this tool.
     

    Man,  analogic + max angle yields pretty fucked color schemes.



  • @dhromed said:

    @da Doctah said:

    I'm 51 years old and still can't figure out why everyone calls a traffic light green when it's clearly white.
     

    Because you're deuteranopic?

     

    Got it in one.  Do you do palms too?



  • @da Doctah said:

    Got it in one.  Do you do palms too?
     

    So the subtleties of my sig are lost on you? :(((

    Why do you call green peppers green, then? Because people all call 'm green even though you find 'em a washed out grey/yellow*?

     

    *) is that right?



  • @dhromed said:

    @da Doctah said:

    Got it in one.  Do you do palms too?
     

    So the subtleties of my sig are lost on you? :(((

    Why do you call green peppers green, then? Because people all call 'm green even though you find 'em a washed out grey/yellow*?

     

    *) is that right?

     

    I call green peppers green because they're not ripe yet.  Based on bitter experience, they never will be ripe.


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