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.
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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.
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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) ~~~~~~
- 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
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) ~~~~~~
More Theories The initial experiments were performed by Faraday, Le Chatelier, Joly, and Reynolds... now we have Bowden, Hughes, Niven, McConica, and Evans, who contributed for a better understanding of sliding friction on ice.
Theory #2.......... Frictional Heating Theory
The "Frictional Heating" theory is popular among today's scientists; that is why there will be a greater emphasis on this concept.
This theory is based on Bowden and Hughes work (1939) which argues against the ineffective "pressure-melting" theory, stating that the layer of water is caused by frictional heating. Further, the low frictional resistance of ice is due to the lubrication of film of water. This theory is accepted by many scientists who devote themselves to this research; however, this theory contains contradicting evidence (we will explore more on this topic as we move on).
Theory #2.......... Frictional Heating Theory
The "Frictional Heating" theory is popular among today's scientists; that is why there will be a greater emphasis on this concept.
This theory is based on Bowden and Hughes work (1939) which argues against the ineffective "pressure-melting" theory, stating that the layer of water is caused by frictional heating. Further, the low frictional resistance of ice is due to the lubrication of film of water. This theory is accepted by many scientists who devote themselves to this research; however, this theory contains contradicting evidence (we will explore more on this topic as we move on).
~~Bowden and Hughes ~~
The great achievers, Bowden and Hughes proved that kinetic friction is the cause of water (which in turn lubricates the "sliding interface"). Obviously, ice isn't completely frictionless as the textbooks assume, and so, friction does exist on the ice and plays a major role (more on the coefficient of friction later on).
As Bowden and Hughes' slider passes by on the ice, energy in the form of heat is produced by the friction. Momentarily, the heat quickly raises the temperature at the interface (contact point); furthermore, a small proportion of this energy is used to melt the ice. Most of the heat or energy is conducted away from the interface to the rest of bodies such as the air, ice, and slider. The film of water soon freezes as the heat is lost.
The great achievers, Bowden and Hughes proved that kinetic friction is the cause of water (which in turn lubricates the "sliding interface"). Obviously, ice isn't completely frictionless as the textbooks assume, and so, friction does exist on the ice and plays a major role (more on the coefficient of friction later on).
As Bowden and Hughes' slider passes by on the ice, energy in the form of heat is produced by the friction. Momentarily, the heat quickly raises the temperature at the interface (contact point); furthermore, a small proportion of this energy is used to melt the ice. Most of the heat or energy is conducted away from the interface to the rest of bodies such as the air, ice, and slider. The film of water soon freezes as the heat is lost.
The "Equilibrium" thickness of water:
Bowden and Hughes states that there is one optimum thickness for the water. For instance, if the water layer is too thin, there will be an increase in friction and the amount of heat. Similarly, if the water is too thick, there is a decrease in friction. (Bowden, 1964)
An Element of Contradiction
Let's assume it is kinetic friction that occurs between a slider and the ice surface, then the material of the slider must have low thermal conductivity so that the heat is stored; moreover,if the slider is an insulator (wood), it will be the best type of material to gather the heat caused by friction and melt the ice surface more efficiently so that the slider can move swiftly; otherwise, as stated previously, a conductor (metal) will indeed transfer the heat away from the interface quickly, resulting in a non-wet surface and a greater frictional force.
Quite surprisingly, our assumptions which are based on simple laws of energy are invalid when it comes to this theory--likewise, the conductors seem to carry low values of friction. ie. blades of skates are metals.
Take Copper for example which is the most effective and efficient conductor of heat; this element characterizes low values of friction on ice.
This is one contradiction which questions the accuracy of the theory.
At this point, it is crucial to apply this knowledge to the blade of a hockey skate-- the blades are stainless steel. Steel conducts heat readily, in which the heat created by friction is dissipated away from the blade (there is less heat available to melt the ice at given contact). From our own experience, the skate blade is indeed designed such that it does its job of giving a smooth slide.
(Perssonn, 1998).
More Theories, below:
Bowden and Hughes states that there is one optimum thickness for the water. For instance, if the water layer is too thin, there will be an increase in friction and the amount of heat. Similarly, if the water is too thick, there is a decrease in friction. (Bowden, 1964)
An Element of Contradiction
Let's assume it is kinetic friction that occurs between a slider and the ice surface, then the material of the slider must have low thermal conductivity so that the heat is stored; moreover,if the slider is an insulator (wood), it will be the best type of material to gather the heat caused by friction and melt the ice surface more efficiently so that the slider can move swiftly; otherwise, as stated previously, a conductor (metal) will indeed transfer the heat away from the interface quickly, resulting in a non-wet surface and a greater frictional force.
Quite surprisingly, our assumptions which are based on simple laws of energy are invalid when it comes to this theory--likewise, the conductors seem to carry low values of friction. ie. blades of skates are metals.
Take Copper for example which is the most effective and efficient conductor of heat; this element characterizes low values of friction on ice.
This is one contradiction which questions the accuracy of the theory.
At this point, it is crucial to apply this knowledge to the blade of a hockey skate-- the blades are stainless steel. Steel conducts heat readily, in which the heat created by friction is dissipated away from the blade (there is less heat available to melt the ice at given contact). From our own experience, the skate blade is indeed designed such that it does its job of giving a smooth slide.
(Perssonn, 1998).
More Theories, below:
These two last theories are least discussed about since the concepts are fairly new and they go beyond the scope of this Independent Study Project.
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)
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)
The 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)
... summary below
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)
... summary below
Original Screenshot, 2001
