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4. Two systems of oscillating tidal forces
The pattern of tide-generating forces is coupled to the position of the moon (or the sun) with respect to the earth. Therefore the whole system rotates so that its axis of symmetry is always directed toward the moon (or the sun). But the axes of symmetry of the two oscillating systems of forces (which produce together the rotating system) have fixed orientations in the reference frame of the earth. With this simulation, you can explore the spatial structure and behavior of each of the oscillating components of the tide-generating forces separately. Click here to make visible only the forces of the first system. (You can do this also by using the corresponding checkboxes on the control panel.)
For this system of oscillating forces (shown by yellow arrows), the axis of symmetry is oriented vertically on the screen. (This system of forces has also a horizontal plane of symmetry.) Click here (or the button "Start") to observe oscillations of the forces. These forces reach their maximal magnitudes four times during a day: this occurs each time the source body (the moon or the sun) passes through zenith and nadir (for the upper point of the globe on the screen), and also at the moments when the body is at the horizon for this point. These forces turn to zero also four times during a day. (Click also here to see the applet.)
For the second oscillating system of the tide-generating forces, which, together with the first system, constitute the rotating system of forces that follows the moon (or the sun) in its daily path through the sky, the axis of symmetry makes an angle of 45 degrees with the vertical direction on the screen. Click here to make visible only the forces of this second system. These forces turn to zero four times during a day: each time the source body passes through zenith and nadir for the point of the globe upper on the screen, and also at the moments when the body is at the horizon for this equatorial point. (Click also here to see the applet.) Author's home page
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The Oceanic Tides – Section 4 (of 8)