The so-called "ideal planet" would have no spin and would be
entirely covered by deep ocean. Suppose that the depth is the
same everywhere, that the viscosity is negligible and that there
is no friction at the bottom of the ocean. In this idealization
bulges would follow the earth-moon axis.
The problem is how to explain the phenomenon in introductory
courses. Arguments based on vector calculus can not be used
in such courses; one is limited to basic kinematics, to the
F=m*a law and to free body diagrams. Oh yes, they also know
that water will position itself to minimize potential energy. So
why is the energy minimized when two bulges have equal size?
Can this question be answered without using advanced calculus?
I do not think so. Most textbooks say that two bulges of equal
size are "expected by the theory" but they do not attempt to
justify this outcome of "more advanced" calculations. In other
words we describe what would happen but we do not explain
it. Those who disagree are challenged to produce a pedagogically
sound explanation for an introductory physics course (or to
calculate the minimal and maximal depths when the depth
without moon being present is given, for example 10 km.)
In my opinion, there is nothing wrong with descriptions without
explanations, as long as we are honest about this. Most of my
students are not equipped with conceptual tools needed to explain
tides. And many teachers, including myself, do not remember
what they learned (long time ago) in advanced courses. The old
saying "you loose it if you do not use it" is applicable here.
Ludwik Kowalski