How heat moves and how temperature is measured
Temperature tells us how hot or cold something is, while heat is the energy that flows from a hotter object to a colder one. A clinical thermometer measures body temperature, usually between 35 °C and 42 °C, and has a kink that stops the mercury from falling back. A laboratory thermometer has a wider range, roughly −10 °C to 110 °C. Normal human body temperature is about 37 °C.
Heat travels in three ways. In conduction, heat passes through a solid from particle to particle, which is why a steel spoon in hot tea warms up. Metals are good conductors, while wood, plastic and air are poor conductors or insulators. In convection, warm liquid or gas rises and cooler fluid sinks to take its place, causing sea breezes and land breezes. In radiation, heat travels without any medium, which is how the Sun warms Earth. Dark surfaces absorb more radiation than light ones.
Why it matters
Cooking pans have metal bases but plastic handles, and people wear light-coloured cotton in summer and woollen clothes in winter because wool traps insulating air. Convection drives winds and the cooling of rooms by ceiling ventilators. Understanding heat also helps explain melting, boiling and the water cycle, and leads to thermodynamics in higher classes.
Key terms
- Temperature
- A measure of how hot or cold an object is, commonly measured in degrees Celsius.
- Conduction
- The transfer of heat through a material from hotter particles to neighbouring cooler ones.
- Convection
- The transfer of heat by the movement of warmer liquid or gas.
- Radiation
- The transfer of heat as waves that need no medium to travel.