  Using a generalized Bohr model and the hyper-spherical formalism for a
three-body system, we derive the Thomas theorem assuming a simple interaction
depending on the range of the potential. We discuss the conditions for which an
unbound two-body system produces a bound three-body system and derive universal
energy functions. We apply our model to $^{4}$He and Triton atoms as well as to
the triton nucleus. Using their scattering lengths and effective ranges, we are
able to reproduce the two-body or the three-body binding energies with only one
parameter fitted. Prediction for excited (Efimov) levels are also given and in
particular we demonstrate that for some hyper-angles two equal minima appear
which indicate a phase (shape) transition similar to the Landau's theory of
phase transition. We suggest that the observed excited levels in two different
experiments for the triton nucleus are indeed Efimov levels and there may be
more surprises.
