With winter set to officially begin in just a couple of weeks, experts from the Jülich Research Center in Germany have published a new study explaining exactly what makes icy surfaces so slick that they can be next to impossible to walk or drive on at times.
In the latest edition of The Journal of Chemical Physics, Jülich scientist Bo Persson proposed a new theory to describe how slippery ice becomes when a hard material such as a ski slides across it. This theory, he said, could help explain the movement of glaciers and other phenomena.
When ice is said to be slippery, it means that it has low friction, and this usually happens when a thin layer of water forms on its surface. This thin water film is usually due to ice melting because of heat from friction, or because of a natural solid-to-liquid phase called premelting which occurs near the surface even when temperatures are below freezing, the study author said.
Complicating matters is the fact that contact between ice and the aforementioned sliding object is usually taking place at an interface between two solids, also called a buried interface. As Persson explained in a statement, it is difficult to directly study the processes happening at the molecular level at this interface because the contact area is blocked by the solid material.
New equation used to describe frictional shear stress of ice
While extensive theoretical and experimental research has been done on the premelting process in the uppermost layers of free ice surfaces, the extent to which these results can be applied to a buried contact area was unclear, according to Persson. To rectify this, he set out to link theories of ice friction to experimental data using a newly-developed equation.
This equation, he explained, describes ice’s frictional shear stress, or the stress it experiences in the presence of contact from a force such as a sliding ski. It showed that shear stress depends on the surface temperature of the ice, and suggests that buried interfaces may exhibit a similar type of premelting behavior as a free surface.
“The most important result is that I have constructed a phenomenological shear stress law which is able to explain ice friction as a function of sliding speed and temperature in a wide velocity and temperature region,” Persson said, adding that the study results to improve our understanding of the physical origins of friction on ice, and why it can be so hard to travel across.
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Feature Image: Thinkstock
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