A Barton's Pendulums experiment demonstrates the physical phenomenon of resonance and the response of pendulums to vibration at,
Below and above their resonant frequencies. In its simplest construction,
Approximately 10 different pendulums are hung from one common string.
This system vibrates at the resonance frequency of a center pendulum, causing the target pendulum to swing with the maximum amplitude.
The other pendulums to the side do not move as well, thus demonstrating how torquing a pendulum at its resonance frequency is most efficient.
data from  [u]http://en.wikipedia.org/wiki/Barton%27s_Pendulums[/u]