Video description: First, the three steady state normal modes are shown, running about a minute each at times: 0:06, 1:07, 2:20. At time: 3:31, oscillation is shown with the initial condition of phi3 – the rightmost pendulum – having a positive magnitude, with phi1 = 0 and phi2 ~= 0.
Description: This demonstration shows the effects of three oscillating pendula connected by springs.
The three normal mode oscillations are shown below, Periods of the normal modes are 2𝜋√𝑔/𝑙 , 2𝜋√𝑔/𝑙 + 𝑘/𝑚, and 2𝜋√𝑔/𝑙 + 3𝑘/𝑚 respectively, where 𝑘 is the spring constant.
For information on the relation between triple spring coupled pendula and the flavor states of neutrinos: https://qmplus.qmul.ac.uk/pluginfile.php/1211583/mod_resource/content/1/Neutrino%20Oscillations%20Pendulum%20Guide.pdf