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A Little History; a Lot of Facts
The force was first described by Gustave-Gaspard Coriolis, a19th-century French engineer-mathematician, in 1835. Coriolis mathematically described why winds pushed in straight lines by pressure differences tended to follow curved paths across the surface of the Earth. In it's simplest terms, as air begins to flow from high to low pressure, the Earth rotates under it. In the northern hemisphere, the wind turns to the right of its direction of motion; in the southern hemisphere, it turns to the left. The force is zero at the equator. Despite his mathematical formulas, Coriolis did not work out what it meant to meteorology. In 1856 an American named William Ferrell applied the Coriolis force to weather patterns in his published theory.
Impact on Weather
Without the Earth's rotation and the Coriolis force, global winds would most likely move in straight lines between points of high pressure and low; however, the Coriolis force and friction against the landscape causes distortions. According to Alistair Fraser of Pennsylvania State University, it is important in meteorology to pinpoint directions of deflections caused by the Coriolis force and other forces such as pressure gradient forces found around areas of high and low pressure in the atmosphere. Fraser points out that the same applies to the oceanic currents.
Drain Debate
One often hears a lot about the Coriolis effect and the direction water rotates as it drains. Indeed, the issue has become one of those urban myths which many believe as fact. The truth, according to Jack Williams, a former USA Today weather editor, in his 2003 article "Understanding the Coriolis Force," is that the Coriolis force is "only for large-scale motions such as winds."
Again, Alistair Fraser of Pennsylvania State University offers a definitive look at what is happening. The rotation taken up by water in a draining sink is determined by the way it was filled, the shape of the basin or vortexes introduced during use. It has nothing to do with the Earth's rotation in either the Northern or Southern Hemispheres.
Impact on Objects
While free moving objects above the surface of the Earth may face some deflection due to the Coriolis effect, most objects on the Earth and those in the skies like planes and spacecraft that have some control over their direction will not. Weaponry fired over extended distances often incorporate projectiles that are considered free moving. Targeting these devices appropriately does often require compensation for the Coriolis force in order to achieve the most accurate deployment.