Depends on the physics model... would an ant-sized human weigh as much as an ant or a human?

Ooh! I have actually experimented with fire scaling myself. To some extent, a scaled down campfire can work, but at a different burn rate. I once made a tiny hearth and experimented for a while at making tiny fires in it. I found that within the range I was trying, a little scale model of a fire that worked well at full scale worked just as well at mini scale, just on a much faster time scale.

For example, if I had a human scale teepee style fire burning, say 1 to 2 inch diameter sticks at about 12 to 18 inches long, I'd need to toss another stick on it roughly every 1 to 5 minutes to maintain a nice blaze. Scaled down to sticks about 1/8th that size, I needed to feed it a stick every few seconds to maintain it. Much smaller and I wouldn't have been able to move my tweezers fast enough to keep it fed.

The interaction of different stick sizes also scales that way. If I was to add a couple of eight inch wide split wedges on that same human scale fire, then once those caught, I could slow down feeding the smaller sticks into it to about 1 every 10 minutes, and still keep the same flame size as long as the larger pieces last. Likewise on the same mini fire as above, I could add a few 1 inch wide split wedges, and slow down to feeding it a little stick every 10 seconds.

The size I was playing with could be considered, say, mouse sized. By the time you scaled down to ant sized, the time scale would be so exaggerated as to be meaningless to compare to human sized fires. This isn't taking into account any additional non-obvious factors that change how it behaves. So no, ant sized campfires are not possible. Mouse sized scale campfires are possible, but only if you tend them constantly and quickly.

Also, I didn't take any precise measurements, I was just making tiny fires to relax. All numbers above are just rough estimates from memory, so you can't really calculate how the scaling works from this, only that is sort of does work, within limits.

If you got shrunk to that size you'd immediately suffocate as your diaphragm would no longer be strong enough to pull enough air into your lungs.

Yes I'm fun at parties.

Upvote purely because the question took me off guard.

I just wanna be a li'l guy with a bitty fire!

Matchsticks for logs. Pine needles for kindling. Human hair from a guy who eats at McDonalds twice a day for tinder!

All because I was the ant to discover fire while some 7 year old human hellspawn melts the rest of my colony with a magnifying glass.

No regrets.

With wood? No burns too fast; volume to surface area differences. But maybe with some sort of high density slow burning fuel. You might be better off with some LEDs though

If you scale a human down to the size of an ant (somehow?), they would quickly die. Our metabolism is very slow, we don't generate enough heat to be alive at those sizes. Since our mass would scale down with the power of 3 and our surface area with the power of 2, the mass to surface area ratio becomes such we would quickly cool down and die.

This among the many many other issues a tiny body would have.

As for creating fire by friction I assume? There needs to be a concentrated amount of energy to create enough heat. Such an energy output would be impossible for something that small.

But say you get a bunch of tiny sticks and somehow also have it catch fire. It still wouldn't work, since the speed the fuel burns is related to the amount of available resources. So you could definitely set some tiny amount of sticks on fire, but it would burn the same as you would do it yourself at current scale. So a little flame, similar to a candle probably and burn that tiny amount of fuel in 3 secs. Compared to the tiny size, the fire would be pretty large.

So no, it doesn't scale like that at all. Scaling stuff like that is all make belief, so you can make up the rules as you go along.

No, fire behaves differently as smaller scales, different fluid dynamics. Everything will appear MUCH more viscose.

For the campfire to scale down like that it also needs more oxygen in the atmosphere. Otherwise you will just get some smoldering wood shavings(or they will turn into a candle fire in size if there enough of them close together). In both cases such campfire will exist for a very short time.

To help answer your question, you can also think about what happens to a fire when you scale it up. This thought experiment will help guide you on whether the scaling is linear, or by volume (cubed) or perhaps even more dramatic than that. In the case of fire, if you imagine a campfire that is 10x the width, 10x the height, and 10x the depth, you are probably looking at a fire that has not 10x the energy, but more like 1000x the energy. It's got a massive energy output compared to a modest campfire, it is going to consume a lot more than 10x as much fuel, and it's potentially going to set stuff on fire and consume it and keep trying to consume more fuel in a way that you wouldn't expect a 10x sized campfire to, and it is a huge emergency that is difficult to put out for that reason. It's not just a 10x bigger fire because you scaled it up in 3 dimensions. It's a vastly bigger monster.

So vice versa, if you're scaling your body from roughly 1.8 meters to 1.8 milllimeters, that's a 1000x reduction, so you might want to take your campfire down to 1/1000th of its human-sized dimensions too. But you're probably not looking at a fire that scales down to 1/1000th with you, you'll be looking at a fire that only has 1/1000th-cubed or 1 billionth as much energy. That is a very small amount of energy, it will barely do anything or even be noticeable at that scale. It may not even sustain a flame. And if you want a campfire with more proportional energy like 1/1000th of a regular campfire for your ant-sized campfire, that means you'll need a campfire that is still 1/10th the physical dimensions of your human-sized campfire. So it's still a really, really big fire relative to your ant-sized body. It's maybe the size of a large candle or alcohol burner, but that's HUGE compared to ant-size dimensions. So no, put quite simply, it doesn't scale like that.

These estimations are approximate and there are probably even more complex scaling factors at play for something as physically complex as fire at such extreme scales, but that should help give you the general idea. You'd probably need much more thorough study and experimentation to get a better idea, unless somebody has already scientifically researched this which wouldn't surprise me.

Yes. Everything scales down. Even broccoli.

Not at all.

Your best point of reference is, without being facetious, the movie A Bug's Life.

You probably could with small enough woody materials, but at that size they'll incinerate pretty quickly unless the density of the woody material in your campfire was equivalent to that of real life to support similar fire behaviour.

Density generally doesn't scale with reduction in size, so what would usually be a solid tree log that burns slowly at 1:1 scale, would probably be equivalent to dry straw or grass blades at 1:200 scale.

(scale numbers spit-balled: no science behind them)

Same principles? Yes. Same ratio of ingredients? Technically yes. (it's the same chemical reactions with the same ratios of input/output)

Though smaller things tend to be easier to light on fire. Think of how things like flour and metal dust are flammable. Steel wool is flammable. You gather small dry brush and twigs to make the foundation for a bigger fire, for crying out loud!

Though you'd be having a lot more problems with your body's biology. Your blood wouldn't work. Wouldn't circulate. Your lungs would feel like you were breathing a thick liquid and also wouldn't work. Your muscles to skeleton ratio would be all out of wack (I 'think' it'd go that you'd have too strong of bones, but I forget how biomechanics scale way up or way down). You'd probably freeze to death very quickly too, even if your biology ran fine.