Recall that the frames of reference wherein Newton's laws hold true are known as the inertial frames. However, there are frames of reference which defy Newton's laws, called the non-inertial reference frames. Non-inertial frames are either accelerating or decelerating relative to the inertial frames. For example, when an airplane takes off, the passengers feel a backward force opposite to the airplane's acceleration. This violates Newton's second law according to which objects are accelerated in the direction of the net external force. In non-inertial frames, inertial or fictitious forces that have no physical origin are necessary to explain the motion of objects. So, in mechanics, it is more convenient to use an inertial frame. Ideally, a frame of reference fixed to the Earth is non-inertial due to its revolution and rotation. However, the forces due to the Earth's rotation are negligible in small mechanical motions but affect large-scale motions like wind patterns. The fictitious force in this frame deflects the wind in the clockwise direction in the northern hemisphere and counterclockwise in the southern hemisphere.