What does a thermometer measure in relation to heat?

A thermometer measures the intensity of heat, which is commonly referred to as temperature. The intensity of heat indicates how much thermal energy an object possesses and correlates directly with the motion of particles within that object. Higher temperatures reflect greater particle motion and energy, while lower temperatures indicate reduced motion and energy.

The other options, such as volume and density, relate to the physical characteristics of substances but do not pertain to heat measurement. Volume refers to the amount of space an object occupies, while density is the mass of an object per unit volume. Duration relates to the time something lasts, which does not connect to the measurement of heat intensity at all. Therefore, the focus on intensity clarifies the specific role of a thermometer in quantifying thermal energy.