Key Takeaways & Executive Findings
- •• • At temperatures below -30 °C, the friction coefficient decreased with increasing speed, attributed to the tearing out of snow grains and granular lubrication, indicating a wear-dominated regime. • • At -8 °C, the friction coefficient increased with speed, attributed to the shearing off of grain tips and thermal softening, suggesting a thermally activated abrasion mechanism. • • Increasing pressure reduced the friction coefficient at both -8 °C and below -30 °C, implying that pressure enhances contact area and promotes granular lubrication or softening. • • The quasi-liquid layer (QLL) does not contribute significantly to ski–snow friction under the investigated conditions, challenging its presumed dominance and highlighting the importance of dry friction mechanisms.
Abstract
The gliding of skis on snow involves multiple coexisting mechanisms, including dry friction, lubrication by frictional meltwater, and capillary suction, complicating the isolation of individual contributions. This study focuses exclusively on dry friction, employing a linear tribometer with a flat slider at -8 °C under conditions where no frictional meltwater was previously observed. To eliminate the influence of the quasi-liquid layer (QLL), experiments were also conducted below -30 °C using dry ice, ensuring dry friction as the sole active mechanism. Additionally, frictional behavior representative of cross-country skiing was investigated. Results show that the friction coefficient decreased with increasing speed at temperatures below -30 °C, but increased with speed at -8 °C. Increasing pressure reduced the friction coefficient at both temperatures. Comparison with theoretical models indicates that the primary friction mechanism is the tearing out of grains below -30 °C, and the shearing off of grain tips (abrasion) at -8 °C. The findings demonstrate that friction under all investigated conditions can be explained by these mechanisms, along with mechanical and thermal effects and granular lubrication, without invoking the QLL. While the QLL is often considered crucial for ice friction, its role in snow friction appears far less significant.
1. Introduction
Conventional ski–snow friction models have long relied on the quasi-liquid layer (QLL) to explain low friction, yet its role on snow remains speculative. Existing experimental evidence is scarce, and isolating dry friction from meltwater lubrication and capillary effects has proven difficult. This study addresses this bottleneck by employing a linear tribometer at -8 °C and below -30 °C, where QLL influence is negligible, thereby enabling direct measurement of dry friction mechanisms.
The experimental protocol systematically varies speed and pressure to map frictional behavior under conditions representative of cross-country skiing. By comparing measured coefficients with theoretical predictions, the study identifies distinct sub-mechanisms—tearing out of grains at cryogenic temperatures and shearing off grain tips at -8 °C—providing a mechanistic framework that excludes QLL contributions. This approach offers a more precise understanding of ski–snow friction, with implications for base material design and performance optimization.
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Shiraz Ahmed Siddiqui, Michael Hasler, Martin Mössner, Joost van Putten, Werner Nachbauer (2026). Investigating Dry Ski–Snow Friction: Mechanisms and Temperature Dependence. SinoTechIntel Verified Research. https://doi.org/10.26599/FRICT.2026.9441260
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Frequently Asked Questions
What are the dominant friction mechanisms at -8 °C and below -30 °C, and how do they differ?
At -8 °C, the primary mechanism is the shearing off of grain tips (abrasion), leading to an increase in friction with speed due to thermal softening. Below -30 °C, the dominant mechanism is the tearing out of snow grains, resulting in a decrease in friction with speed, likely due to granular lubrication effects.
How does pressure affect the friction coefficient at the tested temperatures?
Increasing pressure reduces the friction coefficient at both -8 °C and below -30 °C. This is attributed to enhanced contact area and possibly increased granular lubrication or thermal softening, which reduces shear strength.
What evidence supports the exclusion of the quasi-liquid layer (QLL) in the observed friction?
Experiments were conducted below -30 °C using dry ice, where the QLL is extremely thin (less than 1 nm) and its influence is negligible. The friction behavior could be fully explained by dry friction mechanisms, mechanical/thermal effects, and granular lubrication, without invoking QLL.
Could frictional meltwater have formed at -8 °C under the test conditions?
The study notes that with increasing speed and pressure, the formation of frictional meltwater at -8 °C could not be excluded. However, the experiments were initially designed to avoid meltwater, and the observed friction trends were consistent with dry friction mechanisms.
What are the practical implications of these findings for ski design and performance?
Understanding that dry friction mechanisms dominate under certain conditions suggests that optimizing ski base texture and material to minimize grain tearing or abrasion could reduce friction. Additionally, the negligible role of QLL implies that treatments targeting QLL may have limited impact on snow friction, guiding more effective base preparation strategies.
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