Science Squabbling

Burning some metals leads to perty colours like fireworks and shit, I'd guess it's a similar process.

yeah the combustion products of metals and things, cf inks, can all be made to be prettier.

That one's easy. Blackbody radiation for the main part of the flame (usually blue for candles). and the top part being yellow is due to soot being colder when it burns so different blackbody radiation.

Why does combustion need a spark? isn't heat and oxygen enough?

Fahrenheit 451 says otherwise.

On my reading list.

That one's easy. Blackbody radiation for the main part of the flame (usually blue for candles). and the top part being yellow is due to soot being colder when it burns so different blackbody radiation.

I fairly sure a flame wouldn't be considered a black body.

Racist.

Burning wood releases heat into the gas (air) above it. Heat air up and it glows orangey red. The wood will also release gases, but you'd have to ask a chemist about that.

Wood is mostly carbohydrates and similar large organic molecules, the heat decomposes them into gases which then combine with oxygen in the flame. Depending on the temperature (which depends mostly on the oxygen flow rate), the large carbohydrate molecules are either pyrolysed into carbon (charcoal) or completely combusted, i.e. the carbon chains of the molecules get oxidised into carbon dioxide. Depending on whether your aim is production of charcoal or extraction of energy, you either restrict or force the oxygen flow. In some circumstances, you want to do it in two stages; first, a low oxygen/low temperature pyrolysis to charcoal, which is almost pure carbon, then a highly forced flow through the charcoal which generates higher temperatures than are achievable burning raw wood, for example in a hearth for blacksmithing.

black-body radiation doesn't need to involve a black-body. It just needs something in thermodynamic equilibrium.

What is fire? As in the actual flame. I can understand extreme heating and fast energy release means loss of energy through light and heat and their relationship. But an actual flame, what is it made of?

As i understand it:

In the case of wood, heat causes the complex molecules it's made of to decompose into carbon and volatile flammable gasses such as carbon monoxide, hydrogen, and a whole slew of tars (this is pyrolysis, see also 'cracking' of hydrocarbons). The gasses flow away from the wood until they meet air with oxygen. This is the bottom part of the flame. With access to a bit of oxygen, the gasses burn a bit more and get hotter. The heat causes more cracking to occur and soot (carbon) particles condense while the lighter gasses burn. Unlike gasses which interact with light only at specific wavelengths, the solid soot particles glow brightly with the broad black-body specturm of their temperature - a yellow orange colour - they are what makes the flame bright.

Radiating all that energy away as light rapidly cools the gasses. Maybe enough oxygen mixes in soon enough and the soot burns up, or maybe not.

The initial pyrolysis doesn't need oxygen but does need heat (it's probably endothermic). It's driven by heat radiated back from the burning gasses or from the burning of the carbon left behind by earlier pyrolysis.

Why does combustion need a spark? isn't heat and oxygen enough?

It doesn't. You just need enough heat, or rather sufficiently concentrated heat, i.e. high enough temperature to initiate the burning process in at least one place. Once you have that the fire will make more heat and so the burning process will spread. A spark is just a small thing at a very high temperature. Petrol engines use sparks, diesel engines don't - they just mix fuel and air then get it hot enough to burn.

That one's easy. Blackbody radiation for the main part of the flame (usually blue for candles). and the top part being yellow is due to soot being colder when it burns so different blackbody radiation.

The blue bit isn't blackbody, it's from specific emission bands of the gas molecules.

I had a thought in the shower earlier... It's bugging me...

If matter is mostly empty space, why can't photons/visible light frequencies pass through it?

Apolz if a stupid question, Google has yielded very little in the way of an answer...

Light is a ripple of electric and magnetic fields. Matter may be mostly empty but the bits of it that are there are electrically charged electrons and nuclei. When a ripple of electrical field hits them they move, and when they move they make more ripples of electrical and magnetic fields. The new ripples can cancel out (metals) or disrupt (most opaque things) or just effectively slow down (transparent things) the original ripples.

For fuck's sake moth, why answer if you are just making stuff up. It's obvious you have no idea about any of this stuff. Why don't you let torpid construct or winged angel answer?

Does that mean I was kinda right with both my explanations? I never should have left that first a level physics lesson to do photography because I thought it was cool and girls and stuff.

For fuck's sake moth, why answer if you are just making stuff up. It's obvious you have no idea about any of this stuff. Why don't you let torpid construct or winged angel answer?

He's drawn to it like a moth to a flame.

Why don't you let torpid construct or winged angel answer?
Because ALIENS

First paper accepted for publication this week, boom!

Is it about photons? If not, why not?

No, it's about crayfish because they're awesome.

Is it a study into how they pass through various kinds of matter?

^is the paper about why crayfish can pass through air but not brick?

If not why not?

Could the crayfish pass through clear perspex or glass?

And if it was pink perspex what colour would the crayfish be when it came out the other side?

Is it a study into how they pass through various kinds of matter?

At a high enough velocity they will likely pass through everything.

A fine conclusion. Science 1 - crayfish 0.