Playing with fire


A candle on earth

I remember making candles when I was a kid. We filled empty food cans with paraffin wax – the stuff that comes as a opaque block about the size of a deck of cards. The cans were then put into a bath of boiling water until all the wax melted. A few crayon stubs were added to each can, creating an array of colours. I tied a thick piece of cotton string, destined to be the wick, around a pencil for easy dipping.

Next, dipping (the messy part) could begin. With each dip another layer of wax clung to what was already there, increasing the diameter of the candle-to-be. I rotated through the colours, creating what must have been gaudy candles. When the candle was thick enough to stand on its own, the fun part began: we could light them.

A flaming match held to the exposed end of the wick has enough heat to vaporize wax within the wick and react with the oxygen in the air. Within moments a teardrop-shaped yellow flame flickers to life. The heat from the candle’s flame melts the wax, and the melted wax is drawn up by the wick, sustaining the flame. At its hottest, a candle’s flame can reach 1400 degrees Celsius.

Heat vaporizes the wax creating a gaseous cloud where combustion takes place. Combustion is a series of chemical reactions converting molecules into new combinations – an inefficient process resulting in heat and light. Light, along with its cousin heat, signify the release of excess energy.

Compared to an incandescent light bulb, a candle produces 100 time less light, which is probably why candles are now mostly used to set moods, conduct rituals and provide light in power outages. I don’t often light candles, after all they are one of the leading causes of residential fires and they put soot and chemicals into the air I breathe. But, when I do have a reason to light a candle, I enjoy watching the flickering flame – I find something about it quite mesmerizing.

In my mundane earth existence, when I light a candle the hot gases formed are less dense than the air around them, and so they rise in a process of natural convection into the familiar teardrop shape. This natural convection hinders complete combustion, so soot forms which makes the flame yellow.

Out in my funky futuristic (imaginary) spaceship, where there would be no gravity, natural convection wouldn’t occur, and I would get a perfectly spherical flame. And, the flame would require ventilation or it would smother itself as its temperature would be evenly distributed. (here’s a good, but slightly inaccurate video) On the plus side, the combustion would be complete – so soot would not form. The flame would be bluer and more efficient.

Another effect of gravity on a candle’s flame is the flickering. The frequency squared of a flame’s flickering is proportional to the force of gravity over the diameter of the candle. Meaning that a candle with a smaller diameter would flicker at a faster rate than one with a larger diameter. So a candle on another planet (with different gravity) would flicker at a different rate than the same candle on earth.

A candle on my spaceship wouldn’t flicker at all (I would have to be mesmerized by its pretty spherical blueness instead).

note – this post was originally published back in May 2010 (here)

another note – I downloaded the image from here

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