I was recent asked why the symbol G was used to
represent the modulus of rigidity. My answer was that while Young's
modulus is often represented by a Y (presumably for Young) or
by an E (presumably for Elastic modulus), and The bulk modulus
is often represent by B (again presumably for bulk); I could
think of no good reference for G. I check a number of texts, and found
that while they all without exception used G for the modulus of
rigidity, they also made no reference to why G was used as the symbol.
Perhaps it is just traditional and has no real accountable source.
Does anyone on the list have an answer to this question?