coriolis  force Consider a body which is on a rotating system like  a  merry-go-round. We know that centrifugal force appears due to which the body tends to fly off in a radial direction. In order  to  keep  the  body  rotating, centrifugal  force  must be provided. Consider  now a situation in which a person who is on the  merry-go-round  tries  to move  the  body  along the radial direction. Another force appears on the body which seems to push the body sideways. Therefore a torque will have to be exerted on the body  to  keep  the motion radial. This force which appears whenever  we  move something  on  a  rotating  system is called coriolis force. The coriolis force can be found from

F_c = 2 m w (dr/dt) = 2 m w v

In  certain  situations  the  effect  of  coriolis  force becomes important  for  motion of  bodies  on  earth,  which is rotating counter  clockwise  about the axis passing through the poles with angular velocity w = 7.3 x 10^-5 radians/s.

First  consider  the motion of wind, which is very important in  meteorological studies. The direction of motion of the wind, should be along the pressure gradient, i.e. from high pressure to low  pressure. However in the Northern Hemisphere coriolis force deflects  the  wind to the right of the direction. It is because of  coriolis  force  that winds  around a cyclone (region of low pressure) circulate  in  a  counter  clockwise direction in the Northern Hemisphere and clockwise in the Southern Hemisphere.

The  trajectories of intercontinental ballistic missiles are also  affected  by  coriolis force  and suitable corrections are introduced. Coriolis force also has a role in the meandering of rivers.