See the simple laws of physics at work: Two pendulums swing on a string, transferring energy from one to the other and back again. This demonstration by MarkHacks, made with cardboard, screw hooks, tape, string, and two plumb bobs, allows us to observe the phenomenon with no interruptions.
But what’s going on with the science? Teacher Bruce Yeany demonstrates with more detail and a few other physics demos in Wilburforce & Double Pendulums Demonstrate Resonance from 2015:
Making Lissajous patterns with DIY sand pendulums or light, A pendulum wave demonstration with bowling balls, and Nowhere and Everywhere at the Same Time, No. 2.
In our studies of Harmonic motion, my students always enjoy spending some time building some simple Wilburforce and double pendulums. They all depend on the concept of resonance and help to get the point across very easily. It makes it easier for understanding this concept in other applications where it is not quite as easy to view such as in sound or electrical applications.