Summary
Heat and temperature are not the same. Temperature measures how hot or cold a body is, that is, how fast its particles move; it is measured with a thermometer, in degrees Celsius (°C) or in kelvin (K). Heat is the energy that passes from a hotter body to a colder one.
When two bodies at different temperatures come into contact, heat passes from the hot one to the cold one until both reach the same temperature: this is thermal equilibrium. Heat travels in three ways: by conduction (through a solid, like the spoon in the soup), by convection (in liquids and gases, which rise when heated) and by radiation (without contact, like the Sun's heat). When heated, almost all bodies expand.
Key points
- Temperature measures how hot or cold a body is (thermometer).
- Heat is the energy that passes from a hot body to a colder one.
- Temperature is measured in degrees Celsius (°C) or in kelvin (K).
- In contact, heat passes from hot to cold until thermal equilibrium.
- Conduction (through a solid), convection (liquids and gases) and radiation (no contact).
- The Sun's heat reaches us by radiation, through the vacuum.
- When heated, bodies expand (grow in size).