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MACHO-WIMP
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This may sound stupid but I have always wanted to know what exactly fire is. So can anyone tell me what it is?
MACHO-WIMP said:This may sound stupid but I have always wanted to know what exactly fire is. So can anyone tell me what it is?
Drakkith said:Hrmm. I don't believe your average fire is hot enough to cause a Plasma to form. A match for example only burns at around 1,000 C, which is not hot enough to form a plasma. A blowtorch burns at 1300 C, while a bunsen burner is 1300-1600 C. In comparison, the following are a list of temperatures required to cause something to emit White light.
Whitish: 1,300 °C (2,400 °F)
Bright: 1,400 °C (2,600 °F)
Dazzling: 1,500 °C (2,700 °F)
While the temperature required for ionization and to sustain plasma differes per material, I don't believe these temps will cause much ionization in most materials.
Also, I just found this:
http://www-spof.gsfc.nasa.gov/Education/FAQs7.html#q97
The energy to sustain a fire typically (perhaps always, but I am not sure) comes from an exothermic chemical reaction .
SpectraCat said:Hmmm .. I don't think that is correct. See for example this page:
http://www.plasma-universe.com/Flame
As you can see, there is a picture of a yellow candle flame being deflected in an electric field. That is a characteristic of a plasma. You have a point that combustion flames may not be very good plasmas, in that the degree of ionization is low, but they do seem to have plasma characteristics.
However, I also found this link:
https://www.physicsforums.com/showthread.php?t=203289
As you can see .. this is something of a matter of debate. I haven't finished reading that thread, so I don't know if there was a resolution to the question.
Studiot said:In certain circumstances the energy produced by the burning is spread widely enough and quickly enough to more than just actiate the next particle's burning. Once you have started one particle burning, it will supply the energy to activate the burning of two more, which will activate 2 more each inturn and so on.
This process is known as a chain reaction and leads to an explosion
Are thereconventional explosions that do not operate on this principle? i.e. the byproduct is a solid rather than a gas? Would that be an explosion at all?
Drakkith said:I've read it, and from what I can tell a fire can contain cations and anions, which would react to an electric field. However, the fire does not contain ions and free electrons in sufficient quantitiy to qualify as a plasma. Just because it reacts weakly to an electric field doesn't make it a plasma.
russ_watters said:Moreover, that link is to a site pushing a crackpot view of physics: the "electric universe theory". So it isn't to be trusted.
Studiot said:This process is known as a chain reaction and leads to an explosion - (This does not have to be nuclear to be a chain reaction).
No. What you describe is a deflagration. You have a detonation only if the combustion propagation is supersonic.
Sudden combustion, generally accompanied by a flame and a crackling sound.
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