Bach's Gavotte in g minor is an example of simple binary form. This piece is clearly divided into 2 sections by the double bar line. Section A begins in g minor, but modulates to Bb Major, creating a tonally open section.
The B section begins after the double bar line and serves as a developmental and transitory section. This section is considered to be simple binary form because the A section does not return. There is a motive similiar to that which appears in the A section, but it is in a different key and uses different harmonies. The B section is much less stable tonally than the A section. By the end of the section, we have modulated back to the original key of g minor in order for the piece to serve the simple binary function.