What is fire? 1

[Unotec]

I had my 5 year old asking me if fire is solid, liquid or gas.... I couldn't answer.

What would your answer have been?

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[photoengineer]

What we call fire is the chemical reaction that occurs when a gas reacts with oxygen and heat in its environment. The exothermic reaction produces a visible glow, but the reaction is not a material in an of itself.

Perhaps that is too advanced for a 5 year old...if I had a 5 year old, I probably would have said that fire is a chemical reaction and isn't an element in and of itself.

The ancients said there were four elements: fire, earth, water, and air. Sadly, none of those are actually elements.

Cedar Bluff Engineering

http://cedarbluffengineering.webs.com

 

[photoengineer]

To add a little to my previous response (which was off the top of my head), the flame that we associate with fire is intensely heated gas. When any material (gas, liquid, or solid) gets hot enough, it will emit radiation in the visible light range. The exothermic reaction that is caused by fire heats the gases to a hot enough temperature that they emit visible light which we call flame.

I'll let you translate that one for a 5 year old. But you can think of hot metal that an ironworker is pounding on or liquid metal at a metal foundry, they both glow red.

Cedar Bluff Engineering

http://cedarbluffengineering.webs.com

 

[ivymike]

it's a gas with solids blowing around in it.

 

[zdas04]

What I said to my kids was "hold my beer, I'll look it up".

David

 

[GregLocock]

I just told them to shut up and keep on sweeping the chimney.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[cranky108]

So the apperent fire on the sun is a chemical reaction?

I disagree. Some of what appears to be a fire really isen't anything more that highly heated gas (izonized). Which can occur with out a fire.


So I would say the apperence of a fire is the light from a chemical, nucular, or electrical discharge reaction.

 

[cranky108]

So how did you explain why the sky is blue?

 

[Unotec]

Well, did try to explain the intensely heated gas, but she's my daughter.... and her reply went along the lines of I don't believe you and bodily warm gases being expelled and don't make light.
So what I tried to do was get iron hot enough to show her the glow. Damn pine wood, did not get hot enough and she got bored.
So in conclusion, was I right on fire being gas at a very high temperature emitting a glow as what photoengineer says? It would have to be the glow emitted by N2, I guess, but then comes having to explain the different colourings of the different elements when they burn.
Something somehow doesn't sit right thinking fire is overheated gas. I might be wrong though

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[btrueblood]

She needs more real world experience Unotec. Get busy!

Steel wool and a battery, or a clear light bulb so she can see the filament when the bulb is off, and again when on. Even cooler if you can vary the voltage with a dimmer and show the filament with a dull red glow. Then have her touch the bulb (ouch, thats hot)(yes, much hotter than your body). Stuff has to be really, really hot to glow.

You and I say "duh" to the above, but to a 5-year old it can be a revelation.

 

[ornerynorsk]

You've got to love the simple inquisitive nature of a child. It's too bad that it fades as we grow older.

 

[SomptingGuy]

Fire is moving, reacting gas. The shape and motion of flames is caused by the convection of the entrained air.

What do flames look like in zero gravity? Do they even self-sustain? The combustion products would not naturally move away from the fuel.

- Steve

 

[moltenmetal]

Unfortunately the beautiful natural curiosity of children gets beaten out of them by school and by worry-wart parents. Yeah, I'm guilty of that too as a parent- I think we all are to some extent.

To a five year old: fire is hot gas produced by something burning. You get fire when you combine something which burns, air or something else that has oxygen in it, and something to get it started like a little fire, a spark or something really hot. Fire makes heat, but some fires don't make light that you can see! And you can also use electricity to make light from a gas, and the gas doesn't even need to be hot!

 

[ivymike]

What do flames look like in zero gravity?

http://science.nasa.gov/science-news/science-at-nasa/2000/ast12may_1/

see pic

 

[mauricestoker]

After eating cheap Tex-Mex food for a week, I would say fire is a mixture of gas and liquid.

 

[SomptingGuy]

But to answer the original question...

Magnificent!

If (and it is very unlikely) I ever resort to theism, fire will be high on my list of things that drew me to it.

- Steve

 

[btrueblood]

SG, diffusion drives the 0g flame and transfer of reaction products away from (and reactants to) the flame zone. Much slower process, but since the heat transfer also becomes diffusion-limited, the flames do self sustain. Pinky Nelson helped do some of the research, and gave a lecture to my class in uni. Ask me a question about 0g toilets sometime...

 

[photoengineer]

The sun is not on fire. Fire requires oxygen, which there is very little of in the sun.

The green light radiated from our sun is exactly the same reason as why molten steel is red and a propane flame is blue. The material is at the right temperature to emit red, green, or blue light. Propane gas is on fire (oxygen is combining with propane), while molten steel and our sun are not burning.

The light emitted from flame is a characteristic of the temperature of the gas. The fire itself is a chemical reaction.

Cedar Bluff Engineering

http://cedarbluffengineering.webs.com

 

[msquared48]

So then, from what Photo and Ivy have posted, since the flame is blue in the zerogravity situation, it is hotter in zero gravity than with the yellow flame of gravity?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[SomptingGuy]

Related...

It's getting towards that time (in the Northern hemisphere) when candles should be lit.

If I were a physics/chemistry teacher, candles would provide a lot of my teaching material.

- Steve