Why do hockey players sharpen their ice skates?

Answer: Sharp skate blades cut into the ice to prevent slipping on abrupt turn-arounds.

Ice hockey blades are ground with a groove in the middle of the bade. This shape creates edges on both the inside, and on the outside, of the blade. These inside, and outside, edges provide a grip on the ice for quick turns and stops.

Figure skaters use the "grooved" bade as do hickey skaters because they must execute sharp turns in their dance routines.

 A "flat" blade is the best shape of speed skating, where sudden turns are not involved.

 The sharp edges cut the ice because of the pressure under the blade. As the skate bade moves over the ice the melted ice refreezes. Thus, we see a short ribbon of melted ice trailing skaters.

 The pressure under the blade depends upon the area of the blade. The smaller the blade area the higher the pressure exerted by the skater. For example, a player can exert twice the ice-melting pressure by sharpening his skates to half their area.

 An example of pressure causing ice to melt is the following. Five pound weights are attached to the ends of a steel wire. The wire is draped across a block of ice. The wire slowly pass through the ice block in a matter of days, but without cutting the ice block in halves. The ice had melted under the wire, under high-pressure, but refroze on passing to the wire's topside, where there was no pressure.

 The highest pressures ever created have been in the "diamond anvil". Two diamonds are cut to have needle-points. These diamonds are mounted in a hydraulic press that presses them together needle-point to needle-point. Pressures of 5 million atmospheres have been created in diamond anvils. Amazing phenomena have been discovered by diamond anvils. One such amazing example is that hydrogen gas becomes a metal under such pressure.