system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is ice slippery but glass isn't?
gpt
Most things get smaller when they get colder- it's a principle called "thermal contraction." Most things get bigger when they get hotter- "thermal expansion." Solids are denser than liquids.

Water is weird in that it doesn't work this way. When water becomes ice, it actually because slightly larger because of its molecular structure. Ice forms in a "lattice" of water molecules.

When you step on ice, it physically breaks some of this lattice, compressing it down into water. The water that you just made sort of lubricates the surface of the ice.