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>>"but only for a narrow range of wavelengths..." Curious ; what wavelengths 'carry' the most heat? or capable of carrying the most heat? And what reflective

>>"but only for a narrow range of wavelengths..." Curious ; what wavelengths 'carry' the most heat? or capable of carrying the most heat? And what reflective material/color is best at reflecting most heat? I ask because I used to have a friend who was a physicist at Intel and he couldnt tell me what heat actually was... Do we have an answer to this?

agileAlligator 4y ago
>what wavelengths 'carry' the most heat? or capable of carrying the most heat? Most of heating is from infrared iirc
dekhn 4y ago
It's a bit complicated, but heat is expressed in several ways: in the form of kinetic energy of a system (which is measured by a thermometer), and in the form of infrared radiation emitted by hot objects (which is measured through radiation).
- samstave 4y ago
  Thank you, but what, specifically is "heat" What property of matter is 'heat'
  - dekhn 4y ago
    its kinetic energy. literally the wiggling and jiggling of molecules that gets faster and more intense as you heat things up. When somethign has no heat, it's perfectly frozen at absolute zero.
AlotOfReading 4y ago
Simplifying heavily, Heat is essentially the kinetic energy of the molecules and atoms of a material. It's transferred radiatively at all wavelengths, but shorter wavelengths carry more energy per photon. When those photons are absorbed by a material, the kinetic energy (and thus its temperature) rises. If you want to minimize radiative transfer, you have to maximize the amount of light reflected in the spectrum that's transferring energy and minimize absorption. When something is white, it's diffusely reflecting the entire visible spectrum. That works pretty well for a house in a sunny place, but you don't want to paint the mirrors in your optical cavity white though because there's only a narrow spectrum of light that needs extremely high reflectivity to be usable. For those we use specialized mirrors that can achieve much higher reflectivity over narrow ranges tuned to the application.
zwieback 4y ago
Depending on the temperature of the object there will be a characteristic distribution of wavelengths. It's tricky because a hot object will only radiate specific wavelengths, based on how the heat is generated. That's why the concept of a black body, an idealized thing that radiates a continuous spectrum is used to reason about heat transfer from radiation. Bottom line, there's no single wavelength that carries most heat, it depends on how the heat is generated, what the emissivity of the generating body is and what the absorption of the receiving surface is.
- samstave 4y ago
  So you can tune a body to the emitting source, if it is understood - thus revealing stealth capabilities if you know the radar emission freq? How much is geometry vs material science? We know that anachoic chambers have pyramid-ic structures of foam. So I propose the most stealthy paint would be tiny pyramids of aero-graphene in a spray with a carbon based paint, such that the pyrs absorb bot heat and sound and radio waves.
sbaiddn 4y ago
The photon energy is proportional to its wavelength, but its not relevant. Look up Plank's Law. Its an equation for black body radiation (like, effectively, the Sun). That'll tell you how much heat the Sun radiates at any given wavelength. That's not the same spectrum as falls on your house, the atmosphere has absorbed or scattered some of it. But the distribution that falls on your house is well known. A dielectric mirror is fairly narrow band, compared to this distribution. A dielectric mirror might work well for a factor of two bandwidth, but solar radiation is significant for about a factor of ten. Also dielectric mirrors are: 1. Hard to design 2. Expensive relative to paint 3. Rather fragile compared to paint. Point 3 is important. You can't just pressure wash your siding to clean it without stripping the dielectric mirror. But if you don't clean your siding the mirrors can't reflect the sunlight! As to heat, heat is technically thermal energy transferred from system A to system B by a temperature difference. It has units Joules. In practice it also refers to the thermal energy a system has. Thermal energy is the kinetic energy a material's atoms and molecules have because they're vibrating about. Finally, these are hard questions because they start to hit upon the fundamental definitions in physics and everyday misuse of definitions by physicists themselves. Furthermore laymen have used the word "heart" far before physicists stole the term to refer to something similar but technicals in their field. They did the same thing with the words mass and weight when we needed to distinguish between the force and the mass in the 17th century (its perfectly Ok to say "weight" to refer to mass in most situations including most engineering, chemistry and physics applications)
- samstave 4y ago
  Thank you, but what, specifically is "heat" What property of matter is 'heat'
  - shrimp_emoji 4y ago
    Basically, heat is the thing you say to describe your detection of a transfer of internal energy from an object to its surroundings. E.g., an object's atoms are vibrating a lot, and you touch it, and that vibration spreads to your atoms, so you say you've noticed "heat" in that object. Or the vibrations are emitting radiation (like infrared light) to you, and the radiation begins vibrating your atoms, so you might say "heat is coming off of that object". >Heat is energy in transfer to or from a thermodynamic system, by a mechanism that involves the microscopic atomic modes of motion or the corresponding macroscopic properties. >In the kinetic theory, heat is explained in terms of the microscopic motions and interactions of constituent particles, such as electrons, atoms, and molecules.[57] The immediate meaning of the kinetic energy of the constituent particles is not as heat. It is as a component of internal energy. In microscopic terms, heat is a transfer quantity, and is described by a transport theory, not as steadily localized kinetic energy of particles. Heat transfer arises from temperature gradients or differences, through the diffuse exchange of microscopic kinetic and potential particle energy, by particle collisions and other interactions.[0] 0: https://en.wikipedia.org/wiki/Heat https://en.wikipedia.org/wiki/Heat

agileAlligator 4y ago

>what wavelengths 'carry' the most heat? or capable of carrying the most heat? Most of heating is from infrared iirc

dekhn 4y ago

It's a bit complicated, but heat is expressed in several ways: in the form of kinetic energy of a system (which is measured by a thermometer), and in the form of infrared radiation emitted by hot objects (which is measured through radiation).

samstave 4y ago
Thank you, but what, specifically is "heat" What property of matter is 'heat'
- dekhn 4y ago
  its kinetic energy. literally the wiggling and jiggling of molecules that gets faster and more intense as you heat things up. When somethign has no heat, it's perfectly frozen at absolute zero.

AlotOfReading 4y ago

Simplifying heavily, Heat is essentially the kinetic energy of the molecules and atoms of a material. It's transferred radiatively at all wavelengths, but shorter wavelengths carry more energy per photon. When those photons are absorbed by a material, the kinetic energy (and thus its temperature) rises. If you want to minimize radiative transfer, you have to maximize the amount of light reflected in the spectrum that's transferring energy and minimize absorption. When something is white, it's diffusely reflecting the entire visible spectrum. That works pretty well for a house in a sunny place, but you don't want to paint the mirrors in your optical cavity white though because there's only a narrow spectrum of light that needs extremely high reflectivity to be usable. For those we use specialized mirrors that can achieve much higher reflectivity over narrow ranges tuned to the application.

zwieback 4y ago

Depending on the temperature of the object there will be a characteristic distribution of wavelengths. It's tricky because a hot object will only radiate specific wavelengths, based on how the heat is generated. That's why the concept of a black body, an idealized thing that radiates a continuous spectrum is used to reason about heat transfer from radiation. Bottom line, there's no single wavelength that carries most heat, it depends on how the heat is generated, what the emissivity of the generating body is and what the absorption of the receiving surface is.

samstave 4y ago
So you can tune a body to the emitting source, if it is understood - thus revealing stealth capabilities if you know the radar emission freq? How much is geometry vs material science? We know that anachoic chambers have pyramid-ic structures of foam. So I propose the most stealthy paint would be tiny pyramids of aero-graphene in a spray with a carbon based paint, such that the pyrs absorb bot heat and sound and radio waves.

sbaiddn 4y ago

The photon energy is proportional to its wavelength, but its not relevant. Look up Plank's Law. Its an equation for black body radiation (like, effectively, the Sun). That'll tell you how much heat the Sun radiates at any given wavelength. That's not the same spectrum as falls on your house, the atmosphere has absorbed or scattered some of it. But the distribution that falls on your house is well known. A dielectric mirror is fairly narrow band, compared to this distribution. A dielectric mirror might work well for a factor of two bandwidth, but solar radiation is significant for about a factor of ten. Also dielectric mirrors are: 1. Hard to design 2. Expensive relative to paint 3. Rather fragile compared to paint. Point 3 is important. You can't just pressure wash your siding to clean it without stripping the dielectric mirror. But if you don't clean your siding the mirrors can't reflect the sunlight! As to heat, heat is technically thermal energy transferred from system A to system B by a temperature difference. It has units Joules. In practice it also refers to the thermal energy a system has. Thermal energy is the kinetic energy a material's atoms and molecules have because they're vibrating about. Finally, these are hard questions because they start to hit upon the fundamental definitions in physics and everyday misuse of definitions by physicists themselves. Furthermore laymen have used the word "heart" far before physicists stole the term to refer to something similar but technicals in their field. They did the same thing with the words mass and weight when we needed to distinguish between the force and the mass in the 17th century (its perfectly Ok to say "weight" to refer to mass in most situations including most engineering, chemistry and physics applications)

samstave 4y ago
Thank you, but what, specifically is "heat" What property of matter is 'heat'
- shrimp_emoji 4y ago
  Basically, heat is the thing you say to describe your detection of a transfer of internal energy from an object to its surroundings. E.g., an object's atoms are vibrating a lot, and you touch it, and that vibration spreads to your atoms, so you say you've noticed "heat" in that object. Or the vibrations are emitting radiation (like infrared light) to you, and the radiation begins vibrating your atoms, so you might say "heat is coming off of that object". >Heat is energy in transfer to or from a thermodynamic system, by a mechanism that involves the microscopic atomic modes of motion or the corresponding macroscopic properties. >In the kinetic theory, heat is explained in terms of the microscopic motions and interactions of constituent particles, such as electrons, atoms, and molecules.[57] The immediate meaning of the kinetic energy of the constituent particles is not as heat. It is as a component of internal energy. In microscopic terms, heat is a transfer quantity, and is described by a transport theory, not as steadily localized kinetic energy of particles. Heat transfer arises from temperature gradients or differences, through the diffuse exchange of microscopic kinetic and potential particle energy, by particle collisions and other interactions.[0] 0: https://en.wikipedia.org/wiki/Heat https://en.wikipedia.org/wiki/Heat