system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why is ice slippery?
gpt
First of, when ice freezes, it's usually the flat surface you walk on. It's just really, really flat. Like, a road has tiny bumps and irregularities that cause friction, but a still water surface is completely flat, and so is the water when it freezes.

Secondly, ice is a grid of water atoms. If you squeeze it by walking on it, some of it "collapses" into water, creating a thin layer of water that has even less friction. We use that for ice skating, for example, but that also makes walking on ice even worse.