Demonstrate the harmonic motions of two loosely coupled pendula
Attach two bench rod and clamp assemblies to a cart and space them moderately apart. Attach a rod clamp to each bench rod near the top. On a seperate rod, add two rod hooks which will hold the pendula. Attach the rod with hooks between the two bench rod clamp assemblies utilizing the added rod clamps at the top. The rod with hooks should now be secured and fixed horizontal to the ground. Add the pendula and couple the two together with a weak spring.
Carefully pull one pendula to a side and let go. Watch the observed harmonic motions and how it changes over time. Motions can be in-phase, out-of-phase, and beats.
Energy is transferred through the spring which connects the pendula. The oscillation of the second pendula is driven by the oscillations of the first pendula.