Convection

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Convection current is caused by the expansion of a liquid, solid or gas due to its rise in temperature. The material becomes less dense and rises. As it gets colder, it starts to fall or sink. This starts the cycle of a convection current. This only happens to fluids that's near an energy source that causes it to expand. For example, the movement of water in a pan is driven by a localized heat source. When cool water goes to an edge of a pie pan, the water is dense. It flows around and back to the center. As the water nears the hot metal, it warms again and rises as steam to repeat the cycle. The hot fluid becomes less dense and rises so molecules are carried to a new location. Energy in hot fluid transfers away, fluid contracts becoming more dense, and the fluid flows downward again. Another example are the clouds and the earth. The precipitation goes down, and the heat source makes it rise into the clouds again, which becomes a continuous cycle. The mass of fluid flowing in a circle is a convection cell. This is known as convection. Simply it is the movement of water from a heat energy source and density changes because the fluid's heat changes from the heat energy causing it to rise and sink. Heat from within the earth create convection currents which cause the plates to move, perhaps by a few centimetres a year. Plates may either move away from, towards, or sideways past, neighbouring plates.