What’s a fire, and why does it burn?
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Apparently somewhere else there had been an arson fire and the fire chief was on the stand and the defense asked him what fire was and all he could come up with was "it's hot" or something similar. I don't know if it caused the case to be won or lost but our Chiefs decided we wouldn't chance the embarrassment.
I'll now forever remember that "fire is the rapid oxidation of a combustible material resulting in the release of energy in the form of heat and light".
Still waiting on that subpoena and my chance to put this to good use. Or at least trivia night or something...
Similarly, many chemical fires release substantial amounts of UV, but i doubt anyone would see much of it in an emergency through all the smoke and ir. Think rocket fuels.
Also with radio we talk about different materials being "transparent" to one wavelength or another.
It's a different definition, but it is quite useful in the field.
Also most physicists whose work is centered around EM radiation aren't astrophysicists and plenty of them work specifically with visible light, so your patronization is off the mark.
I'm not sure what is your point. Do you think that saying that the "energy is released in the form of heat and radiation" is better? To me that seems like saying "energy is released in the form of heat (i.e. energy transferred) and radiation (i.e. one the transfer mechanisms)". Do you like "heat (some of which is transferred through radiation (some of which is called light))" better?
The buoyant force on an object is equal to the weight of the displaced fluid.
Well, you might
Does "fire" imply in sustainability? Does it need to be combustion? Does it even have to be chemical?
https://batterybro.com/blogs/18650-wholesale-battery-reviews...
I always tried to get a seat as close to the door as possible.
The first is a 'flashover simulator'. This is a training tool for firefighters to help them recognize the signs of a 'flashover'. A flashover occurs when the radiant heat of the fire is sufficient to cause pyrolysis and ignition of more or less every surface in the room simultaneously (the floor, furniture, etc).
I'm mostly sharing this because sitting in one of these is where it first clicked for me that fire burns gasses, not solids. Watching the fire snake lazily through the smoke overhead, until it felt like I was sitting on the bottom pool, looking up at the surface.
https://www.youtube.com/watch?v=-Z4xxObrTlI&t=40s
The second is Bill Hammack (The Engineer Guy) delivering Faraday's lecture series on The Chemical History of a Candle. This is a truly excellent lecture series, despite its age (they did choose to keep most of the original language, which can take a little getting used to)
https://www.youtube.com/playlist?list=PL0INsTTU1k2UCpOfRuMDR...
Imagine how many lives would be saved if every citizen could experience this kind of training first hand. I think inexperienced individuals are likely to think there is time to gather belongings "while the fire is still scaling". How many of us, upon seeing a fire "slowly" taking over a corner of the room, would believe we have plenty of time to collect our most prized or expensive possessions before running out the door?
Random side thought: I wish we'd come up with a better way of testing evacuation drills. All drills do is teach people that every alarm is fake, and so everyone spends minutes packing up their laptops, grabbing their coats, etc. It's disconcerting to watch people "finishing a block of code", drinking their coffee, or texting on their phone at an office when an alarm goes off. And I've seen that at a company where the executive team planned an unannounced drill 2 months after the scheduled annual drill. As in, nobody knew it was a test. And yet it took 15 minutes to evacuate a small building. facepalm
I'll be the one leaving as soon as the alarm sounds. I've found this also sets an example and people follow.
My school caught fire when I was 12, due to an electrical fault in the basement, and an adjacent building caught fire when I was about 15. University buildings I was in caught fire twice, once late in the evening and once during an exam.
None of these were serious enough that we couldn't reenter the building within several hours, at least to retrieve belongings, but there'd have been no advantage to lingering inside.
As for the drills, you should make it clear to everyone that getting outside (or behind the nearest fireproof door) is their top priority. Hallways are going to be impassable (without passing out at least) after about three minutes, so 15 is definitely too long. I'd probably try to talk to each one of those people you're describing and make sure they understand what they're doing in that case. While they may not value their life much, their employer is on the line if they die during a fire.
A company-wide policy that if you're still inside 5 minutes after the drill starts without a good, drill-related reason (e.g. crowded stairwell), you get your performance bonus cut this month, and if you're still inside 15 minutes after the drill starts, that's ground for firing?
I can't think of anything else that would make people take drills seriously.
An example I remember from my high-school times that particularly annoyed me was teachers who didn't want to let the class go because they were having a test, and test is obviously more important than a fire drill...
> it first clicked for me that fire burns gasses, not solids
Certainly for a standard in-home fireplace fire, most of the outgassing from the fuel is actually water vapour.
A rollover is often the trigger for a flashover.
Somewhat relatedly, the fire inside an internal combustion engine:
That depends on your definition of "burn" and "solid", really. Some fuels only turn into gas due to partial oxidation, or turn directly into plasma - paper would be a good example. Also, solids may have enough surface area to burn all by themselves - coal is a great example here.
Note - from an artistic perspective, and AFAIK, wood (and kerosene, and other sooty fuels) produce a "deep"-looking flame, while propane (and other 'clean' fuels) produce a "shallow"-looking flame, due to the black colors introduced by the soot.
Compare the look of the fire in these propane effects: http://www.effectspecialist.com/special_effects_Propane_flam...
to the look of the fire in this kerosene effect: http://mentalfloss.com/article/71663/watch-mesmerizing-fire-...
This is also (AFAIK) why you generally don't see "sooty" colored flame effects - the amount of the coloring agent that is needed to overcome the "darkening" of the soot is impractical, at least for large-scale effects.
Source: That one time I got really excited the talked to people who'd made a (gigantic) flame tornado art piece.
But your second point seems pretty reasonable; I'm still not sold. Can you go into more detail as to how the presence of glowing soot in one kind of fire - and absence in the other - would create the appearance of solidity (or lack thereof)?
Edit: Sorry, that came out real aggressive. I mean, can you throw some more words at how the glowing soot changes the look of the fire - regardless of the artistic interpretation of the difference?
There are absolutely differences between various flames burning in various conditions. When it comes to burning hydrocarbons (propane, methane, kerosene, gasoline, etc), that difference has more to do with the fuel/air mixture than it has to do with the specifics fuel. It is a lot easier to get a good fuel/air mixture when burning a gas like Propane. When a pool of liquid is burning, it is almost impossible to get a good mixture of fuel and air (even with a bunch of fans), so it is burning fuel rich, resulting in a lot of unburned fuel intermixed with the flame.
I would suggest Periodic Videos recent video about the bunsen burner. They achieve both sorts of flames you're talking about with a single fuel source (methane).
To get back on topic: "Glowing soot" or Blackbody radiation emitted by solid particles in a flame, is by pyrotechnic standards, a washed out flame. Smoke as a background is best not burning. Pretty simple math - to get a red flame of 50 lumens to appear as red when background has gone up to 100 lumens requires a 150 lumen flame. This is why we don't use fireworks in the daylight.
Source: Chapter 11 and 21 in fireworks practices and principals https://exploders.info/Files/Library/eng/pyrotechnics/firevo...
Well, yeah, that would make a way more effective argument, but I'd have to obtain a a) manual camera, b) sizable propane fire c) sizable kerosene/etc fire, d) b & c having nearly identical brightness, and e) a place and time to do it. These are doable, but not on an internet-debate timeline.
Think about the differences in your experience with propane and wood fired fireplaces. Most people have had at least one experience with both, and those are the only things I can think of where the flames in both are of comparable size/brightness.
> Smoke as a background is best not burning I'm sorry, I don't understand. Are you missing a word, maybe?
> [link] Amazeballs link, thank you! Do you know the name of the fireworks that produce large quantities of specifically fire? I know them as "gas bombs", but I have no idea if that's the correct technical term.
Our eyes and brains are very, very good at working at vastly different lighting conditions and presenting the results similarly. That's why they noted that one should use a camera to compare because our eyes are lying to us. (Seriously: Try to guess proper exposure needed for a photo just with your eyes. Even with experience it's hard and you're likely to be off by one or two EV (i.e. a factor or two or four in brightness!)).
However, if you have EXIF info you can probably still compare brightness of flames across photos, as an image's brightness only depends on the actual scene brightness, ISO, aperture and exposure time. And the latter three are merely factors.
1 - The easiest is to spread them over a metal mesh, try not too mix the salts too much.
I had a quantum mechanics professor explain to us the difference between a classical mechanics fireplace and a quantum one. Because in classical mechanics energy is distributed continuously, it would emit gammas,x-rays,etc and would kill you if you could see it. The quantum fireplace would behave as fireplaces do, a much less destructive manner. Fun read.
This article does not cover the history of scientific theory around fire, which is quite fascinating too. Scientists in the 17th century theorized (incorrectly, of course) that fire was an intrinsic property of "phlogisticated" materials [0], which could be burnt to release the phlogiston contained in them. The theory prevailed for over 100 years, until Lavoisier proved that a gas (oxygen) must be present for combustion by measuring the increased weight of phosphorus upon burning [1].
[0] Phlogiston theory: https://en.wikipedia.org/wiki/Phlogiston_theory
[1] Oxygen theory: https://en.wikipedia.org/wiki/Antoine_Lavoisier#Oxygen_theor...
Skimming OP, one thought. My very fuzzy understanding is that, while flame has a spectra shaped like a blackbody curve, it isn't one. Instead, that's the soot emission spectra (due to its diverse mess of bonds). The BBR spectra is much redder and dimmer. This misconception appears widespread.
Meta-observation: Creating fun and correct science education stories is hard, requiring multi-year collaborative effort from many people. It seems a pity there's nowhere on the web to build such.
... Wikipedia has "no original research". The US national science education wiki was/is? just a search engine for high-barrier low-quality paywalled science education magazines. Here in the wretched past, the best we manage to do is accumulate scattered blog and discussion threads. Disrupt, please?
But they do have a "List of common misconceptions" page.
1. http://www.askamathematician.com/2013/05/q-is-fire-a-plasma-...
This is a neat idea that I hadn't heard before!
We just use the atmosphere as a temporary place to store the oxygen, and keep it diluted with enough nitrogen that things don't immediately unphotosynthesize themselves. ;)
And ready to know what the people know / Ask 'em my questions / And get some answers / What's a fire and why does it / What's the word? burn?
[0]https://play.google.com/music/preview/Tgiolwxoj2rmb6sqjvlnph... [1]https://youtu.be/SXKlJuO07eM
I vividly remember my father saying to me at one point, as his response to me making some point about the validity of modern science, that "no one knows how fire works", and that therefore science really wasn't so knowledgeable after all. I remember thinking, "surely if they've figured out atomic fusion, they know how fire works", but I really didn't have a proper response at the time. I had no idea how fire worked. It still seems magical!
Some 30 years later, I finally have the answer...perhaps I should send it to him.
Sure, but what does "sustain combustion" mean? Well, it provides activation energy for reactions. And here's the thing: lack of activation energy is all that keeps us and other combustible stuff from burning.
Scientists don't agree on when humans learned to control fire. Some say 200,000 years ago, some almost 2 million years ago. But clearly, man learned to control and to make use of fire for heating and cooking, for agriculture and as weapons and even for machines long before anyone understood what it is or why it behaves like it does.
Glad to finally get a detailed answer, 39 years later!
Also, the author was only referring to particles when trying to explain the concept of thermal radiation where he is actually speaking of subatomic particles, not of molecules.
TL,DR; Stored chemical energy can be released, by adding to its jiggling- and produces enough energy to cause a jiggling chain reaction to other storages nearby.
> Thermal radiation is produced by the motion of charged particles:
> anything at positive temperature consists of charged particles moving around
I can make sense of your attempted correction by reading "thermal radiation" as "infrared radiation," but those terms don't mean the same thing. Thermal radiation refers to radiation emitted due to a body's temperature, but the peak emission frequency can go up into the visible and beyond if the body is hot enough. (Like the sun and larger stars.) Examples of non-thermal radiation would be e.g. excited state transitions in molecules that produce light in fireflies or the blue light from the lower portion of a candle flame. (The blue part of a candle flame is hot relative to the surrounding air and liquid wax but not hot enough that its thermal emissions would peak in the blue.) Fluorescent and LED light sources also emit visible light by non-thermal processes.
The error in the source is claiming that charged particles are necessary for a body to have a positive temperature (i.e. what I quoted). The error in the downvoting is a kneejerk correction without explaining + not reading in good faith.
I was not one of the downvoters, btw.