Glass is sometimes called a slow liquid, yet it is a solid with a disordered structure.

The longer version

Molten silica cools into a rigid form without ever settling into the neat repeating grid of a crystal. Its atoms are locked in place, but they sit in a jumbled arrangement more like a frozen liquid than a tidy lattice. The material keeps a fixed shape and resists flow, which is what makes it a solid.

The confusion comes from very old window panes that are slightly thicker at the bottom. That unevenness dates from early hand-made sheets, which were never uniform to begin with. At room temperature the flow of this material would take far longer than any human timescale, so no measurable sagging occurs.

Where this entry sits

Everyday physics and chemistry hide small wonders in plain sight, from kitchen reactions to the light in the sky. These short facts explain matter, energy, electricity, magnets, sound, and the simple units we use to measure the world. The full list sits on the Science and Physics page, where every entry is listed in order.