What enables ice skaters to skate fast and why is ice slippery?
I think you are referring to the changes caused in the physical state of ice during ice skating and why ice is slippery.
There are two theories to explain why ice is slippery and why an ice skater can skate at a very fast speed. One states that when a person wearing ice stakes passes over ice, there is heat generated due to the kinetic friction between the stakes and the ice. This melts the ice and creates a very thin layer of liquid water. The layer of water acts as a lubricant and reduces the coefficient of friction to a large extent. This makes it possible for ice skaters to go at very high speeds. As soon as the skater has moved forward, the water layer solidifies back to ice.
Another theory states that when ice is formed water molecules on the top layer of the sheet of ice are not exactly frozen. Due to their vibration, they remain in a quasi-liquid state. This layer of liquid, again, acts as a lubricant reducing the friction between the ice skates and the ice to a large extent.