118
votes
Accepted
Why doesn't increasing the temperature of something like wood or paper set them on fire?
Before answering your question, it is important to understand how ignition of a solid material occurs. For fuels that contain hydrogen and carbon like paper, Ignition is a gas phase phenomenon . It is ...
- 77.9k
103
votes
Why does the humidifier make a stove's flame orange?
OK, this question appears to have generated some controversy. On the one hand is the answer by niels nielsen (currently accepted), which implies that the orange color is from sodium. On the other hand ...
- 29.6k
77
votes
If air is a bad conductor, how does fire heat up a room?
There are three mechanisms at play: conduction, convection and radiation. Radiation is the most immediate. Your environment irradiates you with black body radiation at room temperature (assuming that ...
- 26.6k
76
votes
Accepted
Why does the humidifier make a stove's flame orange?
The explanation I furnish below will stand or fall on the outcome of an experiment I and others here have suggested which is also outlined in my response. I promise to edit or delete my answer per the ...
- 97.8k
68
votes
Bush fires and heat waves, the real mechanics?
This is more a question of chemistry and biology than physics.
Solid objects don't burn (try dropping a lit match on a piece of structural lumber sometime -- it'll just go out). Instead, they ...
- 1,755
59
votes
Accepted
What happens to the mass of a burned object?
You would have much more mass than 100 kg after the wood was burned. As it turns out, wood is made of cellulose and lignin. Both are cross-linked glucose polymers, so a good approximation of what ...
- 12.4k
44
votes
Why does the humidifier make a stove's flame orange?
The water cools the flame to the point where you get incomplete combustion, just like a candle. The yellow light is from glowing carbon, a.k.a. soot.
- 1,516
33
votes
Can I burn a piece of wood by emitting only one photon per second on it?
No. To set fire to a piece of wood you must deliver heat energy to it at a faster rate than it will dissipate. With visible light, the energy of a single photon arriving per second is negligible.
...
- 28.4k
32
votes
If air is a bad conductor, how does fire heat up a room?
Air may be a bad conductor, but it's not that bad a transporter. What I mean, is that the room is heated by a process called convection, and not conduction.
So basically, fire heats up its neighboring ...
- 467
26
votes
Why doesn't increasing the temperature of something like wood or paper set them on fire?
The pan starts out at room temperature, say 20°C. The gas flame starts out around 2000°C. The ignition temperature of paper is roughly 200°C.
So the flame can immediately ignite the paper, but the ...
- 52.2k
26
votes
Can we call rusting of iron a combustion reaction?
Rusting of iron is an oxidation reaction, but not combustion. Although the reaction's equation looks the same as the equations for combustion (e.g., of hydrogen and oxygen mixture, $2\text{H}_2+\text{...
- 64.9k
23
votes
Bush fires and heat waves, the real mechanics?
Water evaporates faster at higher temperatures, so plants will lose water faster in a heat wave than in milder conditions. Drier plants will catch fire easier and burn faster and hotter than moist ...
- 8,541
23
votes
Accepted
The process of burning and increasing weight
For steel wool the combustion reaction is roughly:
$$\require{mhchem} \ce{2 Fe (s) + 3/2 O2 (g) -> Fe2O3 (s)}$$
So the object 'absorbs' (and chemically binds) air oxygen and thus gains weight.
- 35.5k
23
votes
Accepted
Does fire emit black-body radiation?
Different bits of the fire have different characteristics, the spectrum of a flame would usually consist of discrete line radiation perhaps superposed on a weaker continuum. However, the base of the ...
- 136k
21
votes
Fire caused by friction with water
Regardless of the heat source, a material will not ignite unless it reaches, at a minimum, its Self-Ignition Temperature (SIT). In addition to reaching this temperature you need to have the proper ...
- 77.9k
21
votes
Will a piece of coal burn at the atomic level at room temperature?
Yes, but very slowly- probably in the range of ~thousandths of an inch of thickness per year. You can imagine this process as being one of corrosion by chemical attack by oxygen. Because the oxidation ...
- 97.8k
20
votes
What happens to the mass of a burned object?
Depends on what your sack manages to capture
This was a thing that finally helped kill the phlogiston theory of fire (that burning something means releasing the phlogiston enclosed in it): most things ...
- 471
15
votes
Can I burn a piece of wood by emitting only one photon per second on it?
Let's try to calculate that:
The heat capacity of wood is (Wikipedia): $C=1700 \frac{J}{kg K}$ and the temperature at which wood starts to burn is approx $300^\circ C$. Assuming that the wood has ...
- 1,813
14
votes
Why does the humidifier make a stove's flame orange?
The accepted answer is not correct.
I have a gas stove in the basement which I have to do periodic maintenance on. This requires you to remove a bunch of fake logs, which are made out of some very ...
- 8,688
13
votes
What happens to the mass of a burned object?
Relativistic loss of mass is unmeasurable here, but in principle, you’d lose some tiny fraction of the mass by heat transfer to the surroundings.
Whether the smoke would weigh more or less than the ...
- 9,805
12
votes
If air is a bad conductor, how does fire heat up a room?
Preamble
In physics, when one says that something is big/small or good/bad, these terms are never meant in absolute sense, but relative to something else. E.g., we cannot say whether 1 meter is a big ...
- 64.9k
11
votes
Does fire emit black-body radiation?
A good example of profoundly non-blackbody campfire features: the blue flame bases.
they are transparent (not really black in any sense)
they are blue. Their "color temperature" (the best-...
- 8,239
10
votes
Accepted
Burning vs Melting - when applied to cooking chocolate
Olin Lathrop captured something important, which is that the word "burn" does not always align to the chemistry definition of the word. But I did want to answer your question.
Chocolate will burn in ...
- 51.7k
10
votes
Accepted
Does more fire create a hotter fire?
By 500 F I assume you are talking about the ignition temperature of the material being burned when it first ignited, not the temperature of the surface and the flame above the burning material after ...
- 77.9k
9
votes
Accepted
Would blowing someone else's candle out make mine shine brighter?
The claim is certainly true for candles in different rooms. Even in the same room, the effect of one candle on another in terms of oxygen consumption is with all likelihood completely negligible, and ...
- 2,785
9
votes
If air is a bad conductor, how does fire heat up a room?
Probably the most important heat transfer mechanism in the development and spread of a fire in room is radiation which can raise the temperature of the materials in the room to their ignition point. ...
- 77.9k
9
votes
Does fire emit black-body radiation?
The most accurate and at the same time most pedantic answer is that absolutely nothing emits exact black body radiation. It is always an approximation valid at a given temperature in a given frequency ...
- 26.6k
8
votes
Is a flame whistle, pipe organ or flute possible?
Absolutely!
The classic example is the Rijke tube, where a Bunsen flame (in modern versions) acts as an energy source. When the flame is placed at a location where the heat release can couple with ...
- 16.7k
8
votes
Bush fires and heat waves, the real mechanics?
EDIT – Due to the interest, while my previous answer was OK, I’ve summarised official Australian ABC (public broadcaster) Fact Checks on this subject to provide full and correct detail.
The three ...
- 1,496
8
votes
What happens to the mass of a burned object?
Other answers have focused on the combustion products mass, and the mass of oxygen. I want to cover the other part not in those answers. I'm also keeping it very simple, so.bear in mind this isn't ...
- 4,251
Only top scored, non community-wiki answers of a minimum length are eligible