The Cool Science of the Slippery Ice
The idea that someone will say ice is slippery is almost the same as someone telling you that fire is hot. Oh yeah, we already know that is how it works as a child. Those who don't, learned the hard way when we stick our pink finger into the hot stove or oven.
The water under particular temperature solidifies and forms ice. The slippery nature of ice makes it perfect for skiing. The reason that ice is slippery is something no one can pinpoint. It is a grey area much the same way we have not gotten to the bottom of what makes a bicycle stable; we pedal it, and it moves, but up to date no scientist/engineer can very much educate us on why it does not keel over and lose stability.
A road sign warns Users of slippery sature when the temperature drops. Image credits: By By abdallahh from Montréal, Canada (Gaspé)CC BY 2.0 from Wikipedia Commons, Link]
The water as it solidifies to ice expands, some school of thought believes that walking on ice decompresses it into water that forms the slippery effect we experience while standing on ice. This decompression by weight on ice's surface is a flawed one. The human mass produces a pressure that is negligible and not enough to cause the formation of water that is enough to reduce the frictional resistance between the feet and the ice surface.
The Irish physicist, John Joly on December 15, 1886, came up with a theory of why ice is slippery. He published a scientific paper for the Scientific proceedings of the Royal Dublin Society which describes the dynamics that made ice-skating possible. He concluded that pressure of the skateboard liquifies the ice forming a thin water film which makes the ice slippery enough for the skaters to glide through.
John was not alone with this perception that they had deciphered the mystery surrounding the slippery ice, a duo P. Bowden and T.P. Huges, in 1939 did some calculation and concluded that the temperature is the culprit. While Dory believed that the pressure exerted by skaters caused a thin layer of water to decrease friction, Bowden and associate arrived at the conclusion that temperature created due to the friction between the skater's footwear and the ice's surface after observing he kinetic and static friction of various ski material such as the wood and metal.
Though scientists such as Samuel Colbeck disagreed on the premise that the melting of ice under pressure or temperature may have anything to do with the ice's slippery nature as skaters enjoy their game at temperatures as low as -35 degree Celsius. The argument was that at such a low temperature, it would be impossible to produce enough pressure or heat to make the ice melt.
Looking at the graphical representation of the phases of water, we can identify the seven stages out of the 11 phases of water depicted in the diagram. The temperature at which the ice will melt increases with the rise in pressure with an exception made in the low-pressure range.
Some other theory has it that there is open air trapped on one end of the ice that makes the surface of the ice to maintain liquid water. This theory is one that has been proven to be right. However, like the other theory, the water formed is small and hence does not enough to change the frictional resistance of the feet in contact.
Recently a team of researchers led by two brother Prof Mischa Bonn and Prof Daniel Bonn both from the University of Amsterdam in the Netherlands published their findings on why ice is slippery on the Journal of Physical Chemistry titled Molecular Insight into the Slipperiness of Ice on May 9, 2018.
The team dug deep into understanding the slipperiness of ice by conducting measurements over a wide range of temperature covering - 100-degree Celsius to 0-degree Celsius within speeds of 10-6 to 10-1 meter per second. This range far outstrips the efforts of past researchers who conducted similar findings to understand the typical behaviour of ice which differs from other surfaces.
At the end of their research, the results were in. The team concluded that the result has nothing to do with either temperature which melts the ice or the pressure applied to the surface of the ice. But the findings instead points to the molecular nature of the water and the way that ice melts layer-by-layer.
They observed that the surface of the ice has highly mobile water molecules which facilitates the slipperiness of it when it comes in contact with a ski.
This ice outmost layer is thin and behaves like a liquid at temperatures of up to - 30-degree Celsius. With more precise measuring instrument at their disposal, researchers were able to isolate and observe the molecules that exist on this outer layer.
People often erroneously say that scientists are bored individuals always looking for solutions in things that should be left alone or somewhat "thinking too deep" on mundane issues. But that is not true because the study of ice slipperiness is not something that has no usefulness. First, it comes in handy in road safety, vehicle tire traction on icy roads can be better when we understand what the properties of slippery surfaces.
The chemical reactions that occur will further throw more insights into understanding glaciers and the role that ice crystal undertakes in the clouds and its relationship with the ozone layer. Winter sports will benefit immensely from the research also if we can understand more of the complex relationship of the sliding frictions that the ice surface offers over a wide range of conditions.
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