Is glass a solid?

The strange chemistry of this everyday material
20 September 2022


sun shining through a window with flowers in a vase



Katie asks, why is glass not a solid?


Risa Bagwandin answered this question...

Risa - Well, when we hold an object made out of glass, we naturally would think that it's a solid material. However, it's not a true solid for something to be a solid, it needs to have atoms which are audited and that remain fixed in place. Glass is unique in the sense that it has properties of both liquid and solid. It has atoms that are in an ordered structure, but these atoms move rather than remaining fixed in position. So the movements of atoms relative to each other is one of the properties that we know that characterises liquid states.

Chris - There's a claim that if you look at old windows, the glass at the bottom of the frame is thicker than at the top. And people will say, "oh, that's because the glass is a liquid and it's flowed downhill over time. Is that true or false?

Risa - Well, that is false. So the reason why the glass is thicker at the bottom is just because of the placement of the glass on the window pane. So normally when you have a thicker surface at the bottom, it'll be more rigid and be able to be fixed in place securely. In fact, quoting The New Scientist, it would take a billion years for just a few atoms in a pane of glass to shift at all.

Chris - So there you go, Katie.


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