Dec. 24, 2010

Science Dad on the Yule Log and the Chemistry of Fire

by Vince Harriman

Click to enlarge images

Watch the movie above to enjoy a cozy fire with Science Dad, Beckett, and Rowan.

Science Dad thought this would be an easy one, but you know how that goes...

The Fire Triangle

A hundred and whatever years ago (it now seems like...) when I learned about the chemistry of fire, things were much simpler. Maybe because we were dabbing mud on cave walls and we were constrained to two dimensions, I learned that as a chemical process fire needed three things: fuel, oxygen and heat. This was often described as the fire triangle, and was just as often illustrated (thanks to our friends at Wikipedia and Wikimedia Commons for great shareable images!) with the fuel on the bottom of the triangle and heat and oxygen making up the other two legs of the triangle. Simple and neat, the iconography of science back in its infancy was so much easier! Even Beckett, a newly minted six year old, could grasp it.

The Fire Tetrahedron

Fast forward to the future, to the internet and to Wikipedia. It was here that I discovered that I am as old as the caveman or cavewoman who discovered fire, or might as well be. The fire triangle has given way not only to a new image, a new iconography -- it has left the two dimensional world completely behind. We now have the 'fire tetrahedron', a pyramid that is the simplest of the Platonic regular solids, in which each face of the solid represents one of the now four elements necessary for fire: fuel, oxygen, and heat in sufficient quantities to provide the fourth element, which is the chemical chain reaction of combustion that allows fire to feed itself until it has consumed either all the fuel or all the oxygen. Four things. In a pyramid. In which the 'chain reaction' base shoots out toward the viewer like that giant triangular ship in the beginning of Star Wars. How much heat? How much fuel? I felt like the above mentioned caveman or cavewoman scratching my crude triangle on the cave wall.

Armed with this new essential knowledge that fire requires four things in sufficient quantities, Beckett, Rowan and I collected some newspaper, a bit of cardboard, some kindling, and finally some Yule logs -- cherry and oak in this case. Using my antiquated caveman knowledge, we built a (ahem) triangle of fuel, oxygen and heat. We then sat back and marveled at the chain reaction unraveling before us, and enjoyed the fire on a cold winter's night.

In conclusion, fire is a chemical reaction in which combustible materials (anything that reacts quickly with oxygen in the presence of heat) mix with oxygen in the presence of heat in sufficient quantities to produce a chain reaction. At a molecular level the energy supplied by the heat bounces electrons off the fuel and allows the electrons from the oxygen to create a new substance.

But that swap of electrons is only a small part of the story. Our dependence on fire cannot be underestimated -- we may joke about cavemen, but almost every vehicle on the road uses internal combustion to move, and billions of people around the world depend on coal fired plants to produce electricity. Not to mention the billions of people around the world who actually still use fire to heat or light their homes or for cooking. Many of whom, like me, stagger through the world, unaware of the quiet contribution science continues to make to our lives, updating and changing not only our basic knowledge of the world but even its very iconography! The Fire Tetrahedron. What will they think of next?

Have a Happy Holiday! And if you happen to be in Annapolis next week, please join us for the Great Paper Airplane Experiment!

Science Dad, AKA Vince Harriman, is a freelance writer living in Annapolis. His two sons, Beckett-6 (!), and Rowan-2 1/2 ask him 'why' approximately 6,525 times a day.

About Vince Harriman

Science Dad, AKA Vince Harriman, is a freelance writer living in Annapolis. His two sons, Beckett-6 and Rowan-2 1/2 ask him 'why' approximately 6,542 times a day.

The views expressed are those of the author and are not necessarily those of Science Friday.

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