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What is fire





badai
http://www.geek.com/articles/geek-cetera/what-is-fire-20110925/

Quote:



If you’ve got 90 seconds to spare the video above will explain what fire is. It’s an excellent watch, and one that might get you hooked on the Minute Physics YouTube channel.

It might seem like the sort of question a child would ask, but “what is fire?” probably isn’t something you could answer so easily. Sure, there is the text book explanation, involving plasma and something about a chemical process with oxygen, but that’s probably not the explanation most people (definitely not a child) are looking for. The video is quite good at explaining fire in practical terms, or at least more practical than CH4 + 2O2 → CO2 + 2H2O + energy (an example of a chemical process for combustion).

Much of the video is spent talking about the fact that fire glows. This happens because the heat excites molecules, causing light to be released, but did you know that normal candles and lighters (etc.) have a blue glow, but it’s too faint for you to see it? Or that all hot objects glow in some form or another? This isn’t exactly life-changing knowledge but it’s the sort of cool science stuff we (and probably you too) can’t get enough of.

At the end of the video one of the most interesting fast is revealed. We all know that fire move upwards because of gravity, but what would happen in the absence of gravity? Check out the images below of flames burning in microgravity–they lack the teardrop shape we expect to see in a burning flame and simply radiate outward from the center point.



Here is another amazing image of a flame burning in microgravity:



ocalhoun
Well, the microgravity pictures are interesting at least.

Apparently, the flame can't self-organize airflow without gravity to direct the hot gasses upwards.
Makes me wonder... if a slight breeze was blown over the low-gravity candle, enough to start a coherent airflow around it, and then you took the breeze away, would the airflow be able to continue in that direction even without the breeze?
kelseymh
ocalhoun wrote:
Well, the microgravity pictures are interesting at least.

Apparently, the flame can't self-organize airflow without gravity to direct the hot gasses upwards.
Makes me wonder... if a slight breeze was blown over the low-gravity candle, enough to start a coherent airflow around it, and then you took the breeze away, would the airflow be able to continue in that direction even without the breeze?


I don't think it would. The upward flow of the flame is due to buoyancy effects -- heated air is less dense than cool air, and so flows upward. In microgravity, even if you set up an initial flow, there is no pressure gradient to support buoyancy, so you'll just recover the spherical shape when the forced flow is removed.
chatrack
Flame is just like Soul of a living being.
_AVG_
I think I remember posting about this in some other topic ... but anyway, fire is just a combination of heat and light energy, which is released as a product of a chemical reaction (in most cases, combustion). Depending on the reactants, the fire can have different colors.

As far as the movements of flames are concerned, I'd say their shapes depend on the geometrical arrangement of the reactants and how the movement of the reactants change in time (whatever the cause of their movements are; such as wind, etc.)
asnani04
Fire is when heat translates into light and we can see this conversion of energy quite easily. Idea

It is a measure...it is the appearance of heat!!!
ocalhoun
asnani04 wrote:
Fire is when heat translates into light and we can see this conversion of energy quite easily. Idea

It is a measure...it is the appearance of heat!!!


Umm... no.


When you heat up an iron bar until it glows, that is also heat converting into light... but it is not fire.


Fire is a chemical reaction, and the release of light is just one part of it.
(Not even an essential part, if I remember correctly. Things might technically be on fire without making visible flames.)
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