How does pressure affect a thermometer?

Answer 1

Heat is transferred thru the glass of the thermometer to or from the liquid (Mercury) inside. The heat causes the liquid to either expand (hot) or contract. Since the large bulb end contains most of the liquid, but grass doesn't expand as much as the liquid, the expanding liquid forces itself up (if hot) into the narrow tube, which indicated the temperature.

On the molecular level, particles outside the thermometer have a certain kinetic energy (KR) and the particles inside the thermometer also have a certain KE probably a different amount or they are already at the same temperature. Particles (either molecules or atoms) when in either the solid or liquid state, are constantly in motion (for solids, they just vibrate about a fixed, central position. Collision of the particles outside the thermometer and the thermometer itself cause exchange of some KE until the average KE of the outside particles is equal to the average KE of those in the thermometer. When this occurrs they are at the same temp. This change in KE of the particles in the thermometer causes more motion, and this extra motion causes what we call expansion. All molecules in the thermometer are pushing against each other with more force (KE).