Convection facts for kids

Water naturally moving in a pot showing convection currents

Convection is the movement of heat because of the movement of warm matter.

For example, atmospheric circulation moves warm air to cool places, causing wind. Wind, in turn, can enter and cool a room if the window is open. The movement of the clouds, the ocean currents and many types of heaters are examples of convection.

Forced convection and natural convection

Convection can happen naturally ("natural convection") or because of a moving device ("forced convection").

The fan is a device that produces the movement of the air artificially. The air in this case is moving because of the rotation of the fan. This is an example of "forced convection".

Natural convection happens because a fluid is lighter if is hot and it is heavier if is cold, so if a fluid has a hot part and a cold part, the hot part will naturally move upward and the cold part naturally moves downward. For example, if the water in a pot is hotter near the bottom because of the fire, it moves from the bottom to the surface. At the same time the water near the surface is colder so it moves to the bottom.

Convection currents

Convection currents occur when there are significant differences in temperature between two parts of a fluid. When this happens, hot fluids rise and cold fluids sink. This causes movements or currents in the fluid. Atmospheric circulation, for example, is made by convection currents.

Related pages

• Heat transfer
• Heat conduction
• Thermal radiation

Images for kids

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  Simulation of thermal convection in the Earth's mantle. Hot areas are shown in red, cold areas are shown in blue. A hot, less-dense material at the bottom moves upwards, and likewise, cold material from the top moves downwards.

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  Thermal image of a newly lit Ghillie kettle. The plume of hot air resulting from the convection current is visible.

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  This color schlieren image reveals thermal convection originating from heat conduction from a human hand (in silhouette) to the surrounding still atmosphere.

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  Thermal circulation of air masses

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  Idealised depiction of the global circulation on Earth

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  Stages of a thunderstorm's life.

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  An oceanic plate is added to by upwelling (left) and consumed at a subduction zone (right).

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  An illustration of the structure of the Sun and a red giant star, showing their convective zones. These are the granular zones in the outer layers of these stars.

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  A fluid under Rayleigh–Bénard convection: the left picture represents the thermal field and the right picture its two-dimensional Fourier transform.

See also

In Spanish: Convección para niños