The rate of combustion of wood is most directly related to which factor?

• A. Moisture content
• B. Surface area
• C. Temperature
• D. Density

Answer: (B)

The rate at which wood burns is controlled mainly by how much surface is exposed to air. Combustion of a solid fuel occurs at the surface where heat, oxygen, and the fuel meet, so increasing the exposed surface area provides more sites for the burning reaction to take place. That’s why smaller pieces or shredded wood burn faster than a solid log—the edge length relative to volume is much greater, giving a bigger interface for oxidation and heat transfer.

Moisture content slows burning because energy first goes into boiling off water, reducing the energy available to drive the combustion reaction. Temperature can speed up reactions, but it’s a condition that affects all surfaces, whereas surface area directly dictates how much reaction interface exists. Density can influence heat transfer and airflow inside the wood, but it doesn’t control the rate of the surface reaction as directly as surface area does.