Kinds of Currents

Current Definition

• The term "current" refers to the movement of a fluid object -- such as a liquid, a gas, or an electric charge -- in a single direction. A current can flow in a straight path, in a curve or in a complete circle. It also can change direction or stop completely when acted upon by outside forces.

Convection Currents

• A convection current is caused by the heating and cooling of a liquid or a gas. Both gasses and liquids sink when they are cooled, causing a downward-flowing current, and rise when they are heated, causing an upward-flowing current. If a gas or liquid is continuously heated and then cooled, it will form a circular current pattern.

  In the atmosphere, convection currents occur when the sun warms the air, causing an upward air flow. When the air rises high enough to become cooled by the upper atmosphere, it sinks.

  Convection currents also occur in the ocean. As warm water from the equator moves toward the polar regions, it cools, sinks downward, and flows back toward warmer regions, where it rises again. This flow of water stabilizes ocean temperatures.

  Inside the Earth, convection currents occur when hot molten rock flows toward the earth's surface, where it is cooled and becomes dense. This denser material sinks back downward, where it reheats.

Ocean Currents

• There are several types of ocean currents. Surface currents are wind-driven currents that flow in large, circular patterns across the ocean. They reach no more than 1300 feet beneath the ocean's surface. Deep water currents occur far below the ocean's surface. They can be caused by gravity or by changes in water density due to shifts in temperature -- as in convection currents -- or changes in the water's salinity, or salt content. Tidal currents are horizontal currents that flow to or away from the ocean in a straight line as the tide rises and falls. Rip currents are strong currents formed by movement of waves from deep to shallow water.

Electric Currents

• When an electric charge is applied to a conductor, such as a metal wire, the conductor's loosely-bound electrons "jump ship," so to speak, and begin to flow together in a single direction, creating a current that can be used to power appliances. There are two types of currents: DC, or direct currents, and AC, or alternating currents. DC currents are the types of currents you find in a battery. They flow in a single direction. AC currents are the types of currents you find in your home electric socket. They move back and forth rapidly from their power source to the appliance they are powering.

Electric Currents