×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

What is fire?

What is fire?

What is fire?

(OP)
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>>

RE: What is fire?

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

RE: What is fire?

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

RE: What is fire?

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

RE: What is fire?

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

David

RE: What is fire?

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.

RE: What is fire?

So how did you explain why the sky is blue?

RE: What is fire?

(OP)
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>>

RE: What is fire?

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.

 

RE: What is fire?

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

RE: What is fire?

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

RE: What is fire?

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!

RE: What is fire?

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

RE: What is fire?

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

RE: What is fire?

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...

RE: What is fire?

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

RE: What is fire?

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

RE: What is fire?

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

RE: What is fire?

Fire good!

RE: What is fire?

(OP)
ok, so if fire is gas, then if I add enough heat to it, it would glow, correct?

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

RE: What is fire?

Back with the gas thing. I would say it is closer to a plasma.
I say this by the way it conducts electricity.

RE: What is fire?

"ok, so if fire is gas, then if I add enough heat to it, it would glow, correct?" ... no, fire is heated gas ... the gas is air, well, air minus a bunch of the O2 and plus a bunch of CO2.  i'd've thought that someone in the chemical business would've appreciated that fire is a chemical reaction between the fuel (wood, paper) and the O2 in the air.  when there's not enough heat you get incomplete combustion (ie smoke) ... well that my 2c worth

RE: What is fire?

(OP)
rb1957, I agree that fire is the RESULT of a chemical reaction, but not always fuel and O2, is it? And if fire is heated gas and I heat gas (not necessarily through combustion) why would it not glow if fire is nothing but heated gas?

As someone in the chemical business might appreciate, there are several exothermal reactions that do not require the O2 in the air. Such might be the case of Magnesium and water. And there are several more.

Cranky, I did not know fire conducted electricity, quite interesting. But so do many other gases. This characteristic not necessarily makes it plasma, does it? I had an initial thought that fire could be plasma, but then inclined more into the gas theory.

Ok, I guess I was not the only one that could not answer to a 5yr old!

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

RE: What is fire?

Fire is rapid oxidation of a material, which gives off heat, gases, and light.

Flame, which is what some people are trying to define here, is the visible manifestation of (some) fire.  It can be a plasma, depending on the temperature and gases involved, it can also just be very hot (un-ionized) gases.

 

RE: What is fire?

They don't usually give conduction of electricty as feature of a plasma in school. But it is a problem with power lines when brush fires are about.

Also I discovered this when I was younger with a light match and a bug zapper.

RE: What is fire?

I wouldn't have much to do if plasma wasn't conductive.  I work for a magnetron sputtering thn film company.   

RE: What is fire?

Does a sputtering magnetron sound like an electronic Porky Pig?

RE: What is fire?

thx btb ... still laughing at that one !

RE: What is fire?

Unotec,

   I would say that flames are a gas, heated to the point of glowing.  How you heat the gas is not relevant.  It can be a match.  It can be the sun.

   You will have to explain somehow that hot things glow, and that they glow a certain colour at a certain temperature.  

               JHG

RE: What is fire?

what if the fuel is natural gas ?

RE: What is fire?

Cold things glow? Really.

I thought night vision gogles worked off low light provided from other sources. Do they work in underground conditions?

I remember burning alcohol in chemistry class, and there was no visible flame. It did however burn my lab partners hand.

RE: What is fire?

"Cold things glow"

Sure, why wouldn't all objects (that have a temperature above absolute zero) emit radiation? Hot objects emit radiation in the visible light range. Colder objects emit radiation that is of a longer wavelength.
 

Cedar Bluff Engineering
http://cedarbluffengineering.webs.com

RE: What is fire?

Unotec, bodily heat does give off light, only that it is in the infrared spectrum and not the visible light spectrum.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login



News


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close