Why is ice slippery?

It is generally accepted that ice is slippery because ice exposed to the environment often has a thin layer of water above it that acts as a lubricant. It is, however, still an open question why this layer forms.

Some theories have been offered to explain the formation of a thin layer of water above ice. It was originally believed that pressure or friction from an external body, such as a shoe, melts the ice. However, studies have shown that hockey pucks do not generate sufficient pressure to cause the liquefaction of ice. It is now believed that the topmost layer of an ice block exists in a quasi-fluid state because these molecules cannot bond completely with the ice molecules in the block.