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In what follows I will attempt to produce a rigorous, macroscopic, time averaged model of the process of creating fire by friction – up to the point of initial ember formation. I will employ reasonable, practical approximations with the goal of developing mathematical results that are experimentally verifiable. Although force, velocity, pressure and the like are actually vector quantities, due to the symmetry of the problem I will perform a scalar analysis only. Also, to simplify the analysis I will assume that the assortment of variables we will encounter are independent. Mostly this assumption is valid, though on occasion I will point out where the assumption is, or may be weak. I will also occasionally point out where further research and analysis may be of interest to pursue.

There are, of course, a variety of methods for creating fire by friction. This article will focus exclusively on fire drills with solid rotating spindles. The initial analysis will focus on the bow drill, though near the end I’ll describe some modifications that will make the models I’ll develop appropriate for the pump drill as well. I have made no attempt to model the fire thong, fire saw, fire plow or any other method of fire by friction.

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This is a working paper created as an open educational resource, licensed for educational purposes under the Creative Commons Attribution-Noncommercial-No Derivatives license. The author reserves all rights of republication or derivative use.


physics, friction, fire, Firecrafter, Ransburg, University of Dayton Electro-optics and Photonics

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