Conduction, convection and radiation · Grade 9
Energy moves from hotter places to cooler ones in three ways: conduction through solids, convection in liquids and gases, and radiation as infrared waves, which can even cross empty space. Understanding these helps us keep homes warm, drinks hot and engines cool.
Key facts
- Conduction: vibrating particles pass energy to their neighbours; metals conduct best (free electrons).
- Convection: warm fluid expands, becomes less dense and rises; cooler fluid sinks, making a current.
- Radiation: all objects emit infrared; hotter objects emit more. It needs no particles.
- Matt black surfaces are the best absorbers and emitters; shiny silver surfaces are the worst (best reflectors).
- Insulators (trapped air, wool, foam) slow conduction and convection.
- Rate of heat loss through a wall or window = U × area × temperature difference.