To understand snow friction and the sliding mechanism of skis, the absolute temperature at the interface between the ski and snow is required to estimate the ice properties under friction. Maeno (2016) pointed out that the friction coefficient should vary depending on the snow density, grain size, temperature, and so on. Temperature is an important factor required to describe the phase of ice or snow. Interfacial temperature is also required to improve the performance of wax. Previous research reported the temperature variation during downhill skiing using thermocouples (Colbeck, 1994; Warren, Colbeck, & Kennedy, 1989). They evaluated the increase in interfacial temperature according to snow temperature. They concluded that this temperature measurement could be a powerful tool to evaluate the effectiveness of waxes and slider design. In addition, Schindelwig et al. (2014) measured interfacial temperature using infrared temperature sensors. They conducted the experiment in an experimental room with artificial snow conditions to investigate the temperature increase during sliding. They measured a temperature increase of 4.0° C during sliding in two seconds. However, these conventional sensors have difficulty measuring the absolute temperature in principle. Thermocouples measure the temperature difference between the hot and cold junction. Additionally, thermoelectric voltage is normally very weak. In contrast, infrared thermometers measure the intensity of infrared light emitted from the surface of an object. This radiation intensity strongly depends not only on temperature but also the emissivity of the material surface. Our final goal is to understand the relationship between the friction phenomenon and interfacial temperature. In this work, the objective is to determine the interfadal temperature and its variation during sliding by measurement with NTC thermistors, which is a device that changes its electrical resistance with temperature. It is the most accurate sensor that can be mass produced at low cost and fabricated into many different shapes, depending on the application. Recently, we have developed a temperature measurement system with high accuracy on the order of milli-kelvin using thermistors for medical diagnosis (Okabe, Okajima, Komiya, & Maruyama, 2017). We applied our technique to the measurement of interfacial temperature.
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