Final answer:
Most substances contract when cooled and expand when heated, which is essential for the operation of devices such as thermometers. This expansion and contraction are especially rapid in gases, which have large coefficients of volume expansion and generally expand at similar rates.
Step-by-step explanation:
The statement that most substances expand as they are cooled is false. In fact, substances generally expand as their temperature increases and contract as their temperature decreases. This phenomenon of expansion and contraction due to temperature changes forms the operational basis of many thermal devices like thermometers. Gases in particular have large coefficients of volume expansion, which means they expand and contract very rapidly with temperature changes, and most gases do so at roughly the same rate. This varies from liquids and solids which have more diverse expansion rates.
In essence, as the average kinetic energy of the molecules in a substance increases (which happens when the temperature increases), the molecules move more vigorously and tend to take up more space, leading to expansion. Conversely, when the temperature drops, the average kinetic energy decreases, the molecular movements dampen, and the substance contracts. However, there are few exceptions like water which expands upon freezing due to the unique arrangement of hydrogen bonds forming its solid state structure.