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.Ocean Modelling for Beginners Phần 4

Khái niệm về đại dương toàn cầu như là một khối nước liên tục với sự trao đổi tương đối tự do giữa các bộ phận của nó có tầm quan trọng nền tảng cho hải dương học.[3] Các phần đại dương chính được định nghĩa một phần dựa vào các châu lục, các quần đảo khác nhau cùng các tiêu chí khác: các phần này là (theo trật tự giảm dần của diện tích). | 44 3 Basics of Geophysical Fluid Dynamics Rotating Frame of Reference Fig. 3.12 Appearance of straight path white line of an object ball for an observer on a rotating turntable. The inner end of the white line shows the starting position of the object. The SciLab script Straight Path.sce in the folder Miscellaneous Coriolis Force of the CD-ROM produces an animation 3.12.2 The Centripetal Force and the Centrifugal Force Consider an object attached to the end of a rope and spinning around with a rotating turntable. In the f xed coordinate system the object s path is a circle Fig. 3.13 and the force that deflect the object from a straight path is called the centripetal force. This force is directed toward the centre of rotation parallel to the rope and hence Fixed Frame of Reference Rotating Frame of Reference Fig. 3.13 Left panel In the fxed frame of reference an object attached to a rope and rotating at the same rate as the turntable experiences only the centripetal force. Right panel The object appears stationary in the rotating frame of reference which implies a balance between the centripetal force and the centrifugal force. The SciLab script Centripetal Force.sce in the folder Miscellaneous Coriolis Force of the CD-ROM produces an animation 3.12 The Coriolis Force 45 operates perpendicular to the object s direction of motion. The centripetal force per unit mass which is a true force is given by Centripetal force -Q2 r 3.31 where r is the object s distance from the centre of the turntable and Q 2n T is the rotation rate with T being the rotation period. Per definition the rotation rate Q is positive for anticlockwise rotation and negative for clockwise rotation. When releasing the object it will fl away on a straight path with reference to the f xed frame of reference. In the rotating frame of reference on the other hand the object remains at the same location and is therefore not moving at all. Consequently the centripetal force must be balanced by another force