There are three major ways in which energy (heat) moves from one place to another. Two of these are conduction and radiation. The third is convection. Convection occurs in currents. These currents occur naturally on the earth and happen in any substance that is fluid (i.e., that can move), including liquids and gases, according to the Lawrence Hall of Science.
Everything in the environment, whether in nature or artificial, is composed of atoms. These atoms make up bigger pieces called molecules. Convection currents occur because these atoms and molecules get closer together or further apart depending on how much energy (heat) they have.
When atoms or molecules have a lot of energy, they spread out and become less dense. When atoms or molecules have only a little energy, they come closer together and become more dense. In a convection current, less dense atoms and molecules want to rise up. This pushes the denser atoms and molecules out of the way, and these atoms and molecules fall down to take up the original space that the less dense atoms occupied. As a result, the atoms and molecules all start to move in a current.
Convection currents are continuous--that is, they don't stop unless the amount of energy in all of the atoms and molecules becomes equal and the atoms and molecules are about the same density. Since energy sources are common in natural and artificial environments, it can be difficult to stop convection currents completely.
Two major factors impact the flow of convection currents. The first is the amount of energy (heat, temperature) present. The more energy there is, the faster the convection current flows because the denser atoms and molecules quickly can become less dense again. The second factor is pressure. When pressure is very high, it takes much more energy for atoms and molecules to expand and become less dense. As a result, convection currents are harder to start and maintain.
Convection currents are found in many places in the environment and thus have a huge impact. For example, energy from the sun and from chemical processes within the earth creates convection currents in the air and below the earth's crust. As a result, the plates of the earth shift around, and people experience natural phenomena such as earthquakes and volcanic eruptions. Convection currents also carry moisture from one place to another around the world, influencing weather.
People who know how convection currents work may apply them in everyday life. For example, convection currents move rice around in a boiling pot of water, making sure that the rice cooks evenly. Engineers who understand that heat rises as a result of convection currents may build refrigerators with freezers at the bottom so they are more energy efficient, or they may try to design heating and cooling systems with air conditioning units in the upper levels of buildings where convection currents have brought heat.
- Photo Credit professional cooking range with pot image by Canakris from Fotolia.com
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