Is it true that ice skaters actually slide on water instead of ice? Is the pressure from the blade on the ice sufficient to melt ice into water?
Asked by: Gilles Lalancette
This 'explanation' of ice skating is found in many texts, but the numbers don't
support the explanation that it is just a freezing point depression. The reduction
of the freezing point of ice per atmosphere (atm) is -7.4 * 10-3 °C/atm. And the ice temperature
of a skating rink is several degrees lower than the freezing point of water, so the
argument just doesn't hold.
1 atm = 101,325 Pascals = 101,325 Newtons/m2. The average weight of a person is 75 kg which is approximately 750 Newtons. The average blade area of two skates is about 0.003 m2 (assuming that each blade is about 0.5 cm wide and 30 cm long). So the pressure a person is exerting on the ice is: 750 N / 0.003 m2 = 250,000 N/m2 = approx 2.5 atm and would raise the temperature of the ice layer below the blades by only about 0.02 °C.
More current studies show that the structure of ice at the air interface is not the
same as the structure of the bulk. It has some of the character of water because
not all of the hydrogen bonds are satisfied. It appears that this more subtle
effect accounts for the low coefficient of friction of icy surfaces.
Answered by: Vince Calder, Ph.D., Physical Chemist, retired
'Physics is mathematical not because we know so much about the physical world, but because we know so little; it is only its mathematical properties that we can discover.'