Heating, conduction and insulation

Temperature measures how hot something is, in °C. Thermal energy always moves from hotter places to cooler ones until they reach the same temperature. It moves in three ways. In conduction, vibrating particles pass energy to their neighbours; metals are good conductors. In convection, warmer liquid or gas rises and cooler fluid sinks, making a current. In radiation, energy travels as infrared waves, even through space.

An insulator slows the transfer of thermal energy. Air is a good insulator when it is trapped, so wool, foam and double glazing work well. Shiny surfaces reflect infrared and dark matt surfaces absorb and emit it best. A vacuum flask uses a vacuum, shiny walls and a stopper to slow all three kinds of transfer.