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Theory #3........ VAPOUR FILM |
After experimenting with skis, McConica proposed a theory in 1950, stating that it is not water but a film of vapour that exists on the ice surface. This vapour film acts a lubricating agent. Similar to Bowden's theory, water vapour is caused by the heat from friction. However, McConica believes it is vapour, not liquid water, because heat transfer from a vapour to a solid is much slower than heat transfer from a liquid to a solid. This theory in fact declares that thermal conductivity of the material (the ski in McConica's experiments) is unimportant. So McConica feels strongly that gases play a role in friction. (Petrenko, 1995) |
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Final Theory...... Rotational Bearings!!! |
Niven's Theory states that the liquid water on the ice act as ball bearings. He observed the free movement of particles of water; thus there are molecular rotations which accounts for the low friction of a slider on ice. Niven reinforces his theory by explaining that these water molecules don't have the hydrogen bonds to lock them in place; moreover, these molecules may rotate with single bonds. Since he believes that a thin film of water already exists on the ice, heat is not a factor; simply, a slider will glide over the "bearings" without any disturbance.
(Petrenko, 1995)
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Summary: Today, scientists are uncertain which theory is correct; they say that all of them seem to have overlapping arguments, that it may involve more than just two theories to explain the sliding on ice. The "Kinetic Friction" theory is the most popular one at this point in time. Lastly, pressure-melting seems to be ineffective in explaining the sliding of objects on the ice, but it may be a factor for ice when the temperature is just below the freezing point.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~` Here are some tidbits:
-Niven points out that Water that is very close to 0*C and is wet, may in fact act as an adhesive as opposed to a lubricant (many scientists believe that water is a lubricant for a slider on ice).
-Water has adhesive forces due to the process of hydrogen bonding
-whether Water acts as a lubricant or adhesive, McConica illustrates how skis support the presence of "liquid H20" on the ice surface. Skis work better on a wetted surface because of the wax coatings; the wax is simply teflon (polytetrafluoroethylene) which is extremely hydrophobic.
Therefore, the skis freely slide on the film of water! Voila! So water (or vapour according to his theory) does exist!
(Ermakov, 1984)
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