Rabbi: Regarding the recent response to the question about Ice Skating on Shabbat. I wonder, when you answered this question, if you understood the mechanism of ice skating. Because the blades are so thin, when one pushes the skates against the ice, the blades exert pressure against the ice that is high enough to actually melt the ice directly under the blade. This follows from the thermodynamic phase diagram for water. "We therefore actually skate on a thin layer of water, which allows the skate to glide easier." The solid ice is converted to the smoother water, which allows the skate to move forward with less friction. "In Northern Canada, when it is very cold, the increase of pressure from skates is not enough to melt the ice, which is at a much lower temperature. It is therefore hard to skate under these conditions." Is purposefully converting a solid to a liquid permissible on Shabbat? Thank you.
Actually, I was unaware of the exact mechanism of lubricating the ice for the skates. Thank you for the clarification. Nevertheless, turning the ice into water does not seem to pose a problem for Shabbos. The prohibition of turning solid to liquid is a rabbinic prohibition called "molid" and only applies when the liquid is clearly noticible. That is why it is permissible to put ice in a warm glass of liquid (not very hot - that might be cooking) even though it causes the ice to melt, because the melted ice is not discernable inand of itself. The same reasoning applies to the ice, especially since the small amount of water refreezes almost immediately. This may be likened to squeezing juice from a lemon, which is permitted if it is squeezed onto a solid, and does not maintain its liquid form.