^^Pendolo. Links inet.
WolframAlpha
http://www.wolframalpha.com/input/?i=pendulum+period
full pendulum 20°
full pendulum 6°
http://www.wolframalpha.com/input/?i=full+pendulum&rawformassumption=("FS")+->+(("Pendulum",+"T")(&rawformassumption=("F",+"Pendulum",+"l")+->"1+m"&rawformassumption=("F",+"Pendulum",+"q0")+->"6+%C2%B0"&rawformassumption=("F",+"Pendulum",+"g")+->"1+g"&rawformassumption=("FVarOpt")+->+(("Pendulum",+"m")(&rawformassumption=("C",+"full+pendulum")+->+("Formula")
%7B (
%7D )
%22 "
%3E >