system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why is water the only (one of the only?) substances in which its solid form floats on its liquid form?
gpt
Water is a polar molecule. That means one side of it is more positively charged and the other side is negatively charged. When water is in liquid form, the energy and movement of the individual molecules is sufficient to trump the effects of these positive and negative poles.

But as it cools and begins to freeze, the molecules lose energy and the electromagnetic forces from these poles takes over, causing the molecules to arrange in a crystalline structure which is less dense than in liquid form. Since it is less dense, it floats.