In the latest episode of the “Measured World” video series, we uncover what we’re really measuring when we tuck a thermometer under our arm or watch the column of liquid rise behind the windowpane. This is especially useful knowledge at the beginning of summer, when it’s wise to keep a regular eye on the temperature — whether due to scorching hot days, sudden heatwaves, or the threat of summer colds.
“Taking your temperature is a familiar daily routine, but have you ever considered what that number — say, 38.5 °C — actually means?” asks Kristjan Tammik, a research scientist and national standard keeper at Metrosert, in the newest “Measured World” video. He explains that temperature is a physical quantity that describes the thermal state of a body or system. The warmer the body, the higher its temperature. When two bodies are at different temperatures, heat always flows from the warmer to the cooler one until their temperatures equalize.
This principle is exactly how a thermometer works: as temperature changes, certain physical properties — such as volume or electrical resistance — also change. In a classic liquid-in-glass thermometer, the liquid expands when heated, causing the column to rise. In resistance thermometers, the electrical resistance of a sensitive element increases with temperature — by measuring this resistance, the temperature can be determined.
Tammik highlights a crucial nuance: a thermometer always measures its own temperature — not directly that of the surrounding body or environment. Therefore, it’s essential to consider how well the thermometer is in contact with the object being measured.
As an intriguing point, Tammik adds that when it comes to temperature, it’s not quite accurate to talk about “cold” — it’s more appropriate to speak of “less heat.” When we cool something down, we’re removing heat, not adding cold. This perspective helps us better understand the nature of temperature and describe the world more precisely.
Watch the new video to find out why a thermometer always measures itself — and how this helps us better understand the world around us!
“Measured World” is Metrosert’s video series exploring the fascinating world of measurement, dedicated to the 150th anniversary of the Metre Convention. Watch previous episodes HERE.