  The solution to the Euler-Lagrange equation is an extremal functional.To
understand that the functional is stationary at local extrema (maxima or
minima), we propose a physics experiment that involves using soap film to form
a catenoid.
  A catenoid is a surface that is formed between two coaxial circular rings and
is classified mathematically as a minimal surface.Using soap film, we create
catenoids between two rings and characterize the catenoid in-situ while varying
distance between rings. The shape of the soap film is very interesting and can
be explained using dynamic mechanics. By observing catenoid, physics students
can observe local extrema phenomena.
  We stress that in-situ observation of soap film catenoids is an appropriate
physics experiment that combines theory and experimentation.
