Tides

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2. Time variations of tidal forces at different fixed points

As we have seen in the previous section, at an arbitrary fixed equatorial point near the earth, the tidal force is represented by a uniformly rotating vector. The simulation below shows the forces at several points over the earth. Click here (or on the button "Start" of the control panel) to observe the time behaviour of the forces at two opposite points (the upper and the lower on the screen).

We note that these force vectors rotate with an angular velocity twice that of the moon's apparent motion (of the earth's axial rotation), and have opposite directions at any moment. Click here to show also the forces at two more equatorial points. (You can also choose the number of displayed points by checking the corresponding boxes on the control panel.) If you click here, the simulation will show the vectors of forces at eight different points over of the earth. (Click also here to see the applet.) All the vectors rotate synchronously, but the phases of rotation differ. The forces at pairs of opposite equatorial points of the globe rotate with a half-period phase shift and have opposite directions.

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The Oceanic Tides Section 2 (of 8)