# What exactly is fire?

1. Jan 18, 2004

### wasteofo2

Anyone?

2. Jan 18, 2004

### Integral

Staff Emeritus
Flames are the result of oxidation reactions which essentially vaporize the burning material. The vapors resulting from this chemical reaction contain many atoms with electrons in highly excited orbitals. Flames are the visible light emitted by these electrons decaying to lower energy levels. This also explains why different chemicals (materials) have different color flames. The flame colors are determined by the chemical composition of the burning material.

3. Jan 18, 2004

### wasteofo2

You guys make it seem so simple, it's like listening to Robert Johnson...

4. Jan 19, 2004

### Moni

Integral would you clear few things more?

1) After oxidising from where the energy comes to excite the electrons?

2) Different chemical materials has different color flames that means they emitts waves of different wave lengths? then how that is possbile...that the wave lenghts change?

3) Why color depends on the chemecal composition of the burning materials???

5. Jan 19, 2004

### Integral

Staff Emeritus
The chemical reaction releases energy so is self sustaining once started. You use a match to light a piece of paper on fire, the energy supplied by the match starts the reaction, once the reaction is started it releases energy stored in the chemical bonds. The released energy is sufficient to keep the reaction running plus enough extra to provide heat to the surroundings. The reaction which rips apart the chemical bonds must leave many electrons in the constituent atoms in an excited state. These would be the electrons which were initially involved in binding the combustion molecules together.

The dependence of the emitted wavelengths on the chemical is a result of Quantum Mechanics. Every element has a given electron structure, this structure determines the wavelengths that are emitted as electrons cascade to lower energy levels.

6. Jan 20, 2004

### Moni

Quantum Mechanics! But I heard according the QM energy is considered as small Packets...and I mean it deals with particle properties not the wave! May be I am wrong not sure.... :(

7. Jan 20, 2004

### Integral

Staff Emeritus
When we are dealing with light Quantum Mechanics tells us that the energy of a photon must be of the form

$$E= nh\nu$$
Where
$$E = Energy$$
n is an integer
$$\nu= frequency$$
Rearranging we have
$$\nu=\frac E {nh}$$
The various electron orbitals in an atom are separated by discrete steps of energy given by the above equation. When an electron changes from one orbital to another there must be a photon emitted (or adsorbed) with the same energy which separates the 2 orbitals. Can you see that the frequency of the emitted photon is determined by the Energy?

Photons of different energies have different color because frequency is what determines the color of light. A photon cannot be considered a particle like a baseball is a particle, it needs be see as some form of a wave packet of energy. The Frequency or wavelength of the encapsulated energy is determined by the amount of energy encapsulated.

Last edited: Jan 20, 2004
8. Jan 22, 2004

### losang

Fire is that which is hot and burning. Why do you need to explain it in terms of atoms and electrons. Do you think that cave men didn't know what fire was?

9. Jan 22, 2004

### Jimmy

Wasteofo2 already knew that fire was hot and burning. He was looking for the type of answer that Integral gave. He seemed satisfied with the answer. This is a physics forum, after all.

10. Jan 22, 2004

### losang

In that case the question should have said 'how do you explain fire from a physicists point of view?' or something similar.

11. Jan 22, 2004

### Jimmy

When you ask a question on a physics forum, you can expect the answer to be from a physicist's point of view. Like I said, wasteofo2 didn't seem to be upset by the answer. Why are you?

12. Jan 22, 2004

### Njorl

That's pretty much understood. When I post on the caveman forums it is understood that I want things explained in caveman terms.

"Fire good"

Njorl

13. Jan 22, 2004

### Jimmy

You wouldn't happen to be an enlightened Buddhist, would you?

14. Jan 22, 2004

### Integral

Staff Emeritus
This is not an answer to what is fire. When I touch the stove top my finger is hot and burning, so does that mean my finger is fire?

15. Jan 22, 2004

### lan418

How do they make flamethrowers?

16. Jan 24, 2004

### losang

Your finger is not burning because if you remove it from the stove it does not have the ability to maintain the heat. It is only experiencing the pain from touching the hot stove.

17. Jan 24, 2004

### Mr. Robin Parsons

Sure Cavemen knew, they thought it was "Hot and Burning"....but the Question was: "What E-X-A-C-T-L-Y is it" hence the obvious request of a "detailed (more then cave knowledge) responce" cause clearly the cavemen/women DID NOT know the explaination Integral has given....leading edges of knowledge...

18. Jan 24, 2004

### Integral

Staff Emeritus
Here is the trouble with your definition, we have different ideas of what burning means. You have NOT defined the key concept. Just ASSUMED it means the same to you as to everyone else. When I have been in the sun to long I get a sun burn, the skin continues to feel hot and burning for hours after I get out of the sun. Now, what do you mean by hot? What do you mean by burning? Your definition does not provide an answer. Only more questions.

19. Jan 24, 2004

### losang

It does provide an answer. It answers the question of what is fire. Just because questions arise about the meaning of words in the definition does not negate the fact that it answered a question.

20. Jan 24, 2004

### Staff: Mentor

Sure feels like its burning to me. The sensation hasn't changed, so how do I know it isn't burning anymore?

Science has to be more specific than you are being, otherwise our understanding of phenomena decreases with every answer.
I realize you're new here, but how did you miss the name of the forum? In any case, we do have a philosophy forum here - perhaps you'd be more comfortable there.
A flamethrower is a squirt gun with a lighter in front of it. They squirt a flammable liquid (probably something similar to napalm). definition does not negate the fact that it answered a question.