Smoke from a recently extinguished candle demonstrates some beautiful physics. Near the wick, the smoke rises in an orderly way, exhibiting laminar flow. Higher up, interaction with air molecules (which move randomly) breaks the flow into delicate turbulence. [Credit: Jan Gottweiß]Candles have a long association with the Christmas season, so it seemed fitting to talk about the smoke from a candle for today’s Science Advent installment. In this beautiful image, an ordinary candle was lit, then extinguished. The smoke nearest the slightly glowing wick rises in a a coherent pattern: you could trace the path of a smoke particle along a line. This is known as laminar flow, since the layers of smoke don’t mix together. (“Laminar” literally means “flat”, but in everyday usage, we usually mean layered instead, as in laminated paper or wood laminate.) However, air molecules move randomly, so as the smoke rises, it is increasingly buffeted by these other particles. The result is turbulence, where the layers of smoke mix together and billow. Turbulence is fractal in structure: if you could look closely at the smoke, you’d see that turbulence persists on the microscopic level, equally beautiful and equally complex as at the macroscopic level.
[…] In fact, as I promised, the radio image of the galaxy (the stuff in red in the photo above) was produced by the Very Large Array (VLA), a collection of 27 telescopes, each 25 meters in diameter. By working as a single unit, the telescopes in the VLA can map the structures within the plasma jets, revealing their billows, strikingly visually similar (though less turbulent in the absence of air) to those of an extinguished candle. […]
![Smoke from a recently extinguished candle demonstrates some beautiful physics. Near the wick, the smoke rises in an orderly way, exhibiting laminar flow. Higher up, interaction with air molecules (which move randomly) breaks the flow into delicate turbulence. [Credit: Jan Gottweiß]](https://sciencevspseudoscience.files.wordpress.com/2012/12/candle_smoke.jpg?w=500&h=449)
Galileo's Pendulum 
3 responses to “A Smoky Candle (Science Advent 4)”
Did you know: you can relight the candle by lighting the smoke stream. It’s very cool.
I did know that, but you have to be quick!
[…] In fact, as I promised, the radio image of the galaxy (the stuff in red in the photo above) was produced by the Very Large Array (VLA), a collection of 27 telescopes, each 25 meters in diameter. By working as a single unit, the telescopes in the VLA can map the structures within the plasma jets, revealing their billows, strikingly visually similar (though less turbulent in the absence of air) to those of an extinguished candle. […]