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Natural convection is a type of heat transfer wherein non-human forces influence the cooling and heating of fluids, such as gasses and liquids. Heat transfer creates a cycle called a convection current where a warm fluid is replaced by a cooler one. All fluids and matter are made out of tiny building blocks called atoms, which group together in molecules. The movement of these molecules is what causes fluids to rise or fall.
Natural convection helps to explain many of the Earth’s natural systems, such as ocean currents and the atmospheric layers. It is in contrast to forced convection, which works on the same principle but features a heat source created by man-made devices, such as air or water fans that accelerate the heat transfer cycle. Both forced and natural convection can be used for specific purposes, such as heating homes or a municipal water supply.
When acted on by a heat source, such as the sun or underground heat, fluids often rise up. For example, when the sun warms up the surface of the Earth, the air at the ground is almost always warmer than air higher up in the sky. Heat expands the spaces between molecules, making the air lighter and raising it above the surface. As the air ascends farther away from the hot ground, the molecules cool down and compress. This cooler and heavier air is then pulled down by gravity, where it heats up again and starts the cycle anew.
Ocean currents are also created because of natural convection, combined with changes in wind and the density of salt water. Cold winds passing over the water surface cause the molecules to compress and sink down towards the ocean floor. As the water moves closer to the equator, it warms up and rises again. This creates massive ocean currents which flow along continental coasts and affect the weather on the surrounding land regions.
Typically, an important component in natural convection is Newton’s Law of Cooling. This scientific law states that the rate at which a substance loses heat is directly related to the temperature of the object acting upon it. In other words, the colder the object is, the more heat the fluid will lose. One example of this law in action is the effect of adding ice cubes to a drink — one cube will only take away a small portion of heat, but a handful will chill the drink much faster.