|If the thermometer works on the concept of liquids expanding when heated, how can the glass not expand as well. I mean, the glass expands, maybe the thermometer gets longer, or the hole in the middle where the liquid is, gets smaller or larger or something but the glass must also expand, so why does the thermometer work or does it? — RP, Hotchkiss, Colorado
You're right about the glass expanding along with the liquid inside it. But liquids normally expand more than solids as their temperatures increase. That's because the atoms and molecules in a liquid have more freedom to move around than those in a solid and they respond to increasing temperatures by forming less and less tightly packed arrangements. Since the liquid in a thermometer expands more than the glass container around it, the liquid level rises as the thermometer's temperature increases.