Is There a Connection Between a Burning Log and E=mc2?


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Photosynthesis: Stored Sunlight

In another of his wonderful talks, physicist Richard Feynman tells us that burning a log is kind of like the photosynthesis process in reverse.

Put simply, a tree takes in energy from sunlight, carbon dioxide from the air, and water from the ground to produce carbohydrate molecules made of carbon, hydrogen, and oxygen. The tree also releases oxygen molecules into the air in the process.

Burning a log, on the other hand, breaks up these carbohydrate molecules, which then combine with oxygen in the air to produce carbon dioxide and water. This process gives off energy in the form of heat and light — reducing the remaining log and its byproducts’ weight by E=mc2.

Converting Mass to Energy

So, to answer the reader’s question: Energy from sunlight is stored in the making of a tree, and released in the energy of heat and light given off in burning it — all governed by E=mc2.

For a more detailed and fun explanation of the chemistry of fire, check out the video What is a Flame.

Sunlight powers photosynthesis. With chlorophyll as catalyst: nCO2 + nH2O + energy → CnH2nOn + nO2
Image Credit: ClipartPal


FireWoodResource. Firewood BTU Ratings Charts for Common Tree Species. Accessed December 18, 2012.

Ames, Ben. What is a Flame. Alan Alda Flame Contest Winner, Center of Communicating Science, Accessed December 18, 2012.

Pössel, Markus. From E=mc² to the atomic bomb. Einstein Online Vol.4 (2010), 1004. Accessed December 18, 2012.

Wolfson, Richard. Simply Einstein, Relativity Demystified, Norton, New York (2003), p. 155.

Carter, J. Photosynthesis. (1996). University of Cincinnati. Accessed December 18, 2012.

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