Coriolis Force is an apparent force caused by the Earth's rotation. The coriolis force is responsible for deflection of winds towards the right in the northern hemisphere and left in the southern hemisphere. It is also known as Ferrel's law, and is responsible for deflection of the south-east trade winds which enter the Indian peninsula as the south-west monsoon. The Coriolis effect (also called the Coriolis force) can be defined as the apparent deflection of objects (such as airplanes, wind, missiles, and ocean currents) moving in a straight path relative to the earth's surface. Its strength is proportional to the speed of the earth's rotation at different latitudes but it has an impact on moving objects across the globe.
The Coriolis effect is caused by the rotation of the Earth and the inertia of the mass experiencing the effect. When Newton's laws are transformed to a rotating frame of reference, the Coriolis and centrifugal forces appear. A rotating frame of reference is a special case of a non-inertial reference frame (a frame of reference that is under acceleration) that is rotating relative to an inertial reference frame (a frame of reference that describes time homogeneously and space homogeneously). Both forces are proportional to the mass of the object. The Coriolis force is proportional to the rotation rate and the centrifugal force is proportional to its square. The Coriolis force acts in a direction perpendicular to the rotation axis and to the velocity of the body in the rotating frame and is proportional to the object's speed in the rotating frame. The centrifugal force acts outwards in the radial direction and is proportional to the distance of the body from the axis of the rotating frame. These additional forces are termed either inertial forces, fictitious forces or pseudo forces.
The mathematical expression for the Coriolis force appeared in an 1835 paper by a French scientist Gaspard-Gustave Coriolis in connection with the theory of water wheels. Coriolis showed that, if the ordinary Newtonian laws of motion of bodies are to be used in a rotating frame of reference, an inertial force--acting to the right of the direction of body motion for counterclockwise rotation of the reference frame or to the left for clockwise rotation--must be included in the equations of motion. That paper considered the supplementary forces that are detected in a rotating frame of reference. By the early 20th century the effect was known as the "acceleration of Coriolis". By 1920 it was referred as "Coriolis force". Early in the 20th century, the term Coriolis force began to be used in connection with meteorology.
Coriolis force is an outcome of inertia, and is not attributable to an identifiable originating body, as is the case for electromagnetic or nuclear forces, for example. Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. The Coriolis effect exists only when one uses a rotating reference frame. In the rotating frame it behaves exactly like a real force (that is to say, it causes acceleration and has real effects). From an analytical viewpoint, to use Newton's second law in a rotating system, Coriolis force is mathematically necessary, but it disappears in a non-accelerating, inertial frame of reference. For example, consider two children on opposite sides of a spinning roundabout (carousel), who are throwing a ball to each other. From the children's point of view, this ball's path is curved sideways by the Coriolis Effect. Suppose the roundabout spins counter-clockwise when viewed from above. From the thrower's perspective, the deflection is to the right. From the non-thrower's perspective, deflection is to left. Another example is nausea due to an experienced push. This may be more clearly explained by Coriolis force than by the law of inertia.
At a given rate of rotation of the observer, the magnitude of the Coriolis acceleration of the object is proportional to the velocity of the object and also to the sine of the angle between the direction of movement of the object and the axis of rotation. The vector formula for the magnitude and direction of the Coriolis acceleration is a_{c} = -2 Ω * v, where, ‘a_{c}’ is the acceleration of the particle in the rotating system, ‘v’ is the velocity of the particle in the rotating system, and ‘Ω’ is the angular velocity (which specifies the angular speed of an object and the axis about which the object is rotating) vector which has magnitude equal to the rotation rate ‘w’ and is directed along the axis of rotation of the rotating reference frame, and the * symbol represents the cross product operator. The equation may be multiplied by the mass of the relevant object to produce the Coriolis force: F_{c} = -2 m Ω * v, where, F_{c} is the Coriolis force.
The Earth's rotation causes the surface to move fastest at the equator, and not at all at the poles. A bird flying away from the equator carries this faster motion with it—or, equivalently, the surface under the bird is rotating more slowly than it was—and the bird's flight curves eastward slightly. In general: objects moving away from the equator curve eastward; objects moving towards the equator curve westward.
In meteorology and marine science, the centrifugal and Coriolis forces are introduced. Their relative importance is determined by the applicable Rossby numbers. An apparent force that acts outward on a body moving around a center, arising from the body's inertia is known as the centrifugal force. The Rossby number is the ratio of inertial to Coriolis forces. A small Rossby number signifies a system which is strongly affected by Coriolis forces, and a large Rossby number signifies a system in which inertial forces dominate. For example, in tornadoes, the Rossby number is large, in low-pressure systems it is low and in oceanic systems it is of the order of unity. As a result, in tornadoes the Coriolis force is negligible, and balance is between pressure and centrifugal forces. In low-pressure systems, centrifugal force is negligible and balance is between Coriolis and pressure forces. In the oceans all three forces are comparable. In the northern hemisphere of the planet, above the equator, objects moving on the surface can be observed veering to the right. In the southern hemisphere objects veer to the left. Meteorological events, such as hurricanes, typhoons, and jet streams, are good examples of phenomena influenced by Coriolis force.