Triple Point of Water

While the concept of the triple point is important to the understanding of phase diagrams, the real life application of waters triple point is extremely limited. The only commonly known example is that of an ice skate on ice. The pressure of the persons body applied over the area of the skates blade, increases the pressure on the ice. A simple principle (Gibb's Phase rule) states that the increase in pressure favors the formation of the more dense phase, which in this case is water. The film of water between the skate blade and the ice is what the person skating glides upon. This is why the blades are designed with the width that is used. It is also why people who skate on double bladed skates commonly find it difficult to skate.

As can be seen on the phase diagram of the triple point of water, the triple point temperature is 0.01 °C, and the pressure is 4.56 mm Hg (.006 atm). It is the closeness of the triple point temp to the freezing temperature of water that allows just a persons weight over the area of the blades to make use of this property.

Andrew Johnson 4/28/96

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