# Physical Science How much does fire weigh?

Discussion in 'Physical Science' started by Iggy, Jan 24, 2005.

Is it possible to tell me how to figure out how much fire weighs? It cannot be a gas, for it is fire, and fire is fueled by gasses. It cannot be heavy, because fire seems to float upwards, (hot air rises). But at the same time it cannot be lighter than air, because of the simple fact that it stays fixed to the material it is consuming. (example: fire stays on logs burning in fireplace) Fire contradicts itself. A Physics Professor told me once that the question, "what does fire weigh?" is something only taught to physics majors that are in their second semester of their senior year. He never gave me a straight answer. Can you help me figure out how much fire weighs? Thank you for your time.

2. ### Al VerecoMember

I won't pretend to know what I'm talking about, but:
I always thought fire was a form of energy, and that energy had no weight. I suspect that fire/flames/hot air rises because of gravity rather than it's weight in relation to air. Because: The Sun is basically a big ball of flame, and all of it's flames go up (relatively)... even though there is no air. Although I guess you could argue that it's lighter than hydrogen, etc, I suppose... I would tend to think, though, that fire/heat acts as a kind of anti-gravity, but - as I said - I don't really know anything about it.

As far as fire 'staying on' the log, it's kind of like saying that a waterfall 'stays on' the cliff. Yes, it does, but it's never the same water from one moment to the next. Rather, it's a flow of water. With fire, a flame appears, 'flows' upwards and gradually dies out. Meanwhile other flames appear and do the same thing. Etc. To the best of my knowledge, anyway! :D

I have been checking around... This answer seems to be the same at most science sites...... I actually do not think it is easy to answer, I guess we have to know all the chemicals and surroundings that have contributed to that particular fire in the first place.

The reason you can not see it rise up away from the fire like you mentioned is because the gas gets its energyfrom the electrons moving about in the atom and as they move about they give off energy in the form of light. The different substace being burned will give off different colors of light. Most organic material is composed of Carbon and the caborn acting with the oxygen gives off the red, yellow orange light/ Also as the gas rises away from the main source of fuel and heat the particles and atoms loose energy as the energy decreses the atom can no longer give off light for it has no energy.

Fire has mass... otherwise it wouldn't exist. Therefore it must have weight. I have thought and thought on this for a long time. It seems to contradict itself doesn't it?

I wondered if someone could come up with a mathematical equation of some form to help me out?

Maybe by using something like this, someone maybe able to come up with an answer:

Get a candle... preferably one that is long, they burn better and the candle can be weighed after it is put out.

Weigh it...

Light it...

Let it burn for five minutes...

Blow it out...

Weigh the candle again...

It seems like the weight of the remaining candle taken from the original weight, somehow could tell us of the combustion rate, and would have something to do with figuring out how much fire itself in mass is produced... thus figuring out exactly what fire would weigh.

It seems simple but I keep getting stuff wrong. Wish I had listened in science class now...

Yah, I have checked alot of science sites. The difficult thing about measuring is that there are many factors contributing to the fire itself.

The size and thickness of the wick, the makeup of the wick, the same with the candle, also, we must figure out how much humiditiy (moisture) there is in the air, probably the temp and altitude at the time as well. The composition of the ratio of chemicals in the air would need to be conducted as well. It think this sort of experiment could only be controlled in a lab that is able to control all of these aspects, problably as well as many aspects that I have not even thought of...

All that happens is basically the energy from the heat breaks down the candel into carbon and oxygen and releases it into the atmosphere. Remember

Law of consorvarion mass- Matter can never be created or destroyed

Law of conservation energy - Energy can never be created or destroyed.

AND

E=MC^2 - Energy and matter are interchangeable enrgy can be turned into matter and matter to energy.

Just because something is lighter than air doesnt mean it doesnt have weight. Look at your table perodico Oxygen is like 16 AMU and Hydrogen is 1AMU it is still there and has mass.

Gases are considerd fluids also. In water something sinks because it is more dense than water. The reason things dont float in air is because they are more dense than air. IF a compound/ element is lighter than aiir it is lifted up. Look at the halogen gases. Some are really light some are really heavy some drop to the ground like a pound of bricks som rise like uhh a light halgon gass... yea thats it...

Get that much?

Thanks for the information. Then if the right information was carefully gathered, then maybe it would be possible? Sure would be something I would love to do... is figure out how much fire weighed... Oh well, I won't give up on it though. I guess I have a few things to study before I try to attempt any experiment... huh? lol Thanks everyone... maybe one day I will post here again with a really cool answer... In the meantime, if anyone wants to try to find out exactly how much a 'measured unit' of fire weighs, have fun, be careful and please post back here to let us all know too...

9. ### Keven412New Member

hey, i stumbled upon this blog about the weight of fire looking for how hot a pic lighter gets and read what you all have wrote. I'm not very smart at things like this but if you say fire comes from fuel turning into gases that then combust and perduce heat and light..... then the weight of the fire is the weight of THAT gas while loosing atoms and gaining new ones while burning. that is if you counting FIRE as the red yellow and orange part you want to weigh.

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10. ### Derek■֎؜♫■Staff Member

Hi Kevin412, Thanks for your input on this.

Now I think I may have to go dig out the old meter that measures grams and weigh a small candle unlit than light it, if anything I would think the weight would diminish as some of the candle is converted to gas...

Well, I am certainly not going to try to lift it to find out...

This is a really DumB analogy, however this thread is not, it's one of the best I've read in a while. So here goes with my misguided analogy:

It's tough to weigh things that are in a changing state, as is fire, as most of us know, when the soon-to- be defunct Space Shuttle re-enters the Earth's atmosphere, there's a period of uncertainty, right? Always a time when mission control has to, ....sort of wait.

13. ### chopstickNew Member

Fire is a chemical reaction to oxygen, heat and combustible material. Smoke is a by product of the reaction and will weight the same as the loss of weight of the combustible material. ~ I think~

You guys are definitely on the right track. I think the important part is to not actually think of fire as a "thing." It's energy, plain and simple, essentially the same as what happens when you turn on a lightbulb. The light emitted by the bulb is caused by the filament inside being heated to the point that it glows - the same happens with the molecules within a combusting substance, except that the reaction there is constantly creating a completely new substance (or set of substances).
I guess the answer is that fire causes a negative change in mass, because some of the mass within the combusting substance is being emitted as heat and light energy.

15. ### Derek■֎؜♫■Staff Member

These are all some great posts! I am really enjoying reading this thread. :D

I think, and never got a chance to try it before the gram scale I had disappeared, once fire is introduced to the substance there may be a rapid increase in weight (albeit a small increase due to the oxygen and other surrounding molecules) until the substance starts converting due to the combustion...

Photons escaping from chemical bonds produce the illumination we see however, if you accept the theory of relativity, then it would seem that the actual weigh of "fire," would depend upon the "observer," if you will. Factors such as flash point, ambient temperature, and environmental variables must also be considered. The atomic weight and mass of the substances involved in the energy transformation of the excited ion state would also seem to be variables when attempting to discover an accurate measurement tool.