Use of ‘chalk’ in rock climbing: sine qua non or myth?
In an effort to stay on top of the science we’re posting all known scientific research around chalk use in climbing. This article is pretty old (2001) & surprisingly concludes that “chalk does not work”. The article claims that magnesium carbonate decreases the coefficient of friction by creating a slippery granular layer between the skin and the rock. This post is part of a series where we highlight the existing research around chalk.
This confirms our own experience: using too much chalk actually decreases the perceived friction but correctly applied in a thin layer it tends to improve friction.
Abstract, emphasis ours: Magnesium carbonate, or 'chalk', is used by rock climbers to dry their hands to increase the coefficient of friction, thereby improving the grip of the holds. To date, no scientific research supports this practice; indeed, some evidence suggests that magnesium carbonate could decrease the coefficient of friction. Fifteen participants were asked to apply a force with the tip of their fingers to hold a flattened rock (normal force), while a tangential force pulled the rock away. The coefficient of friction--that is, the ratio between the tangential force (pulling the rock) and the normal force (applied by the participants)--was calculated. Coating (chalk vs no chalk), dampness (water vs no water) and rock (sandstone, granite and slate) were manipulated. The results showed that chalk decreased the coefficient of friction. Sandstone was found to be less slippery than granite and slate. Finally, water had no significant effect on the coefficient of friction. The counter-intuitive effect of chalk appears to be caused by two independent factors. First, magnesium carbonate dries the skin, decreasing its compliance and hence reducing the coefficient of friction. Secondly, magnesium carbonate creates a slippery granular layer. We conclude that, to improve the coefficient of friction in rock climbing, an effort should be made to remove all particles of chalk; alternative methods for drying the fingers are preferable.
PubMed Link Photo by Damir Spanic
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