Final answer:
Convection is caused by temperature and density differences that result in the rise of warm, less dense fluid and the sinking of cool, denser fluid, creating a convection current. This current is a critical mechanism for heat transfer, operating in both natural and forced environments.
Step-by-step explanation:
Two factors that cause convection are temperature differences and density differences in fluids (gases and liquids). Heated material becomes less dense and rises, whereas cooler, denser material sinks. This movement creates a convection current, which efficiently transfers thermal energy. Natural convection is driven by these buoyant forces and is commonly observed in phenomena such as the warming of a house or the motion of water heating on a stove. Alternatively, forced convection involves the movement of fluid by external means, like a fan or pump, as observed in heating systems and weather patterns.
The movement of mass in a convection current follows this pattern: the warmer and less dense fluid rises, and as it transfers its heat to the surroundings, it becomes cooler and denser, eventually sinking back down to be reheated once more. This cycle continues, creating a loop of upward and downward motion which facilitates the transfer of heat from warmer regions to cooler ones, sometimes even with a phase change involved in the process.