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That example sounds wrong. My understanding is that the black ball will heat up more quickly because it's converting a wider range of light frequencies into hea
by meruru 8y ago
That example sounds wrong. My understanding is that the black ball will heat up more quickly because it's converting a wider range of light frequencies into heat. The color isn't affecting heat conductivity and thus shouldn't affect how quickly it cools down at night.
- phonypc 8y agoNot conductivity, but emissivity. In theory anyway, I'm not sure if plain black paint would make a difference.
- ethbro 8y agohttps://physics.stackexchange.com/questions/159856/why-is-black-the-best-emitter https://physics.stackexchange.com/questions/159856/why-is-bl...
- meruru 8y agoI used to think that the darker the object, the more light it was turning into heat. Is that idea just plain wrong or is there some correlation? Are dark objects dark just because the light they emit are in an invisible frequency range?
- Zenst 8y agoThe colour of an object we see is based upon light refracted back. So if an object is black it is absorbing most of the light, and the classic grass - which appears green is actually absorbing the red and blue spectrum and reflecting back the green light - appearing green. "Are dark objects dark just because the light they emit are in an invisible frequency range?" the light they reflect back may well encompass the non visible spectrum, after all that's how radar works and the drive for radar absorbing materials by the military. So not all objects that for us in out limited light spectrum visual senses are equal, even if they look the same - black. May be one reflects back UV, one may absorb it. So for a true picture you would need to see an absorption graph of the full spectrum (visible and non visible). Crux is - objects we see via refracted light - we are seeing in negative. So whilst we see green grass, it's true colour is everything but green.
- phonypc 8y ago>So whilst we see green grass, it's true colour is everything but green. I've never liked this phrasing. In what sense is the "true" color not green if we perceive green? It is the color it reflects, it's just a little counter-intuitive when you first learn of the physics behind it.
- Zenst 8y agoYes I will conceed it is far from an ideal way of describing how things are and with that, somewhat subjective in perception. For me, it gets down to physics and how we perceive things. From a human perception aspect - the true colour of grass is green. But when you add the science aspect, it is not that clear cut. Somewhat gets down to context. For me - if an object emits light - that's it's true colour. Equally how it refracts light is the perceived colour. Objects that emit light have a true and perceived colour the same. Though there is always other factors like whats in between the object and the light (be that refracted or emitted). The sun and sky being good example of that at play. But equally even at a small scale, the air will have an impact, even if we can not perceive it. But yes, we're all human and with that, you are right in that the true colour from our perception shows grass is green. So I'll try and refer to grass as its true colour of green and it's physics colour as red/blue. Which feels perhaps a better way of phrasing and one I'll try and run with until something better comes along.
- goodcanadian 8y agoLight coloured objects are light coloured because they are reflecting most of the photons that hit them back to your eyes. Dark coloured objects are dark because they are absorbing more of the photons. This is why dark coloured objects heat up faster in the sun; they are absorbing more photons. However, generally, the converse is also true, objects that readily absorb photons also readily emit them. So, the dark object will cool down more rapidly in the shade or at night. The wavelength (or colour) emitted depends on the temperature of the object. At room temperature, the emission peaks in the infrared, so the object still appears dark (but will glow brightly in night vision goggles). As it gets hotter, the peak emission moves into the visible spectrum and the object starts to glow (red hot then white hot).
- benj111 8y agoI have a nice nerd snipe. Is it better for the inside of a fridge to be black or white? Discuss.
- yxhuvud 8y agoWhite, because it allows you to clean it effectively.
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- Dylan16807 8y agoI don't understand what you think there is to ponder deeply here. A fridge body is a pure insulator so the answer has to be white. Also it barely matters because convection will cool the surface anyway. Super straightforward with no math to do or conflict to resolve, unless I'm missing something.
- abakker 8y agoAs long as the door opens vertically (vs being the lid on a trunk like a deep freezer) it doesn’t much matter. Refrigerators really need to recover cold air more than focus on absolute perfect insulation. I’ve always thought that we should just all move to the refrigerator-as-a-bunch-of-independent-drawers design. I think it would be easier to browse efficiently and easier to design a kitchen around.