Which term refers to the model of tides that postulates an Earth with uniform depth ocean and instantaneous response to solar and lunar gravity?

• A. Dynamic Theory of Tides
• B. Equilibrium Theory of Tides
• C. Flood Current
• D. Lunar Tide

Answer: (B)

Understanding how tides are modeled: the equilibrium idea treats the ocean as a uniform-depth sheet that responds instantly to gravity from the Moon and Sun. In this simplified view, the gravitational forces create two bulges on opposite sides of the Earth, so as the planet rotates, locations move into and out of these bulges to produce tides. This model ignores real-world factors like changing ocean depth, coastlines, seabed topography, and the time it takes water to move—so it’s an idealized baseline rather than a description of actual tides.

That’s why this term fits: it’s specifically the description of tides in an idealized, uniform-depth ocean with instantaneous response to the gravitational forcing. The Dynamic Theory of Tides, by contrast, accounts for how water actually moves as waves, with inertia, friction, and coastline effects, which is why the term wouldn’t describe the instantaneous, uniform-depth assumption. Flood Current is just a phase of flow during rising tides, not a theory of tides, and Lunar Tide refers to the lunar component rather than a modeling framework.