Page 20 - Science Focus (issue 15)

Are there alternative explanations? It was
suggested that frictional heating could be
another key to ice melting. According to Bowden
and Hughes’s paper published in 1939, they
experimented with wood and metals in a research
center, which was located at 3 346 m above sea
level in Switzerland. They found that the coefficient
3
of friction and its corresponding heat conduction
can provide a novel explanation to the melting
of ice. However, Colbeck rebutted this theory in
his abovementioned article. In Colbeck’s formula,
the contact length between the blade and the
ice surface is conversely proportional to the rate
of heat generation by frictional heating per unit Extraordinary
area. The numerical result shows that, if the rate
of heat generation by frictional heating has to
be equivalent to that of pressure melting, which Science:
is already negligibly small, the length of blade
which is in contact with the water membrane T he Mechanism of
must be 15 μm (i.e. 15 x 10 m), assuming that the
-6
skating speed is 5 m/s. The length of a normal
blade is 30 cm, and 15 μm is only its 0.005 % (no 科學不一樣： 探討溜冰的奧秘
one would skate with a 15 μm long blade, right?).
The numerical analysis has proven that the effect
brought by frictional heating is much smaller than
that resulted from pressure melting. It can thus only
be also one of the mechanisms that allows us to Pennsylvania State University accept Faraday’s
skate on ice. idea, but he also raised a model in 1951 to explain
the arrangement of water molecules in both the
Then, what is the main reason for the ice to core and surface of an ice cube. From there,
melt? Conventional wisdom suggests that water different research laboratories conducted various
doesn’t melt below 0 °C, but such an ingrained quantitative research to test this idea in 1950s. This
belief is indeed the culprit that hinders us in finding enables theoretical and experimental physicists to
another possible reason! From 1850, Faraday, a investigate how much pressure, frictional heating
British physicist, has started a series of experiments and the liquid-like film on the surface contribute
about regelation. He put two pieces of ice together to ice melting respectively under different
so that they are in contact with one another. temperatures.
The two pieces of ice then adhere together and
become one. Faraday therefore discovered that In 1969, Prof. Orem and Adamson from the
there is a liquid-like film, which plays a key role in University of Southern California further discovered
the freezing of ice, on the ice surface subsequently. that the premelting of the ice surface starts from -35
This also leads to the subsequent research on the °C through the analysis of the physical absorption
4
thickness of liquid-like film on the ice surface . of vapors. This confirms the existence of a liquid-
like film on the ice surface. With the advancements
A century after Faraday’s discovery, another in technology, its existence was further confirmed
scientist, Prof. Gurney, suggested in 1949 that by nuclear magnetic resonance (NMR), proton
the intrinsic liquid-like film surrounding the ice backscattering and X-ray diffraction. Nonetheless,
is a key factor that affects the slipperiness of the role played by the liquid-like film in ice skating is
ice. In addition, not only did Prof. Weyl from the yet to be confirmed by further research.