Free-fall acceleration experiment in vacuum:
Section 5. Harmonic Oscillators, Pendulum
A simple pendulum:
Interactive simulation of a forced harmonic oscillator at this link.
Double pendulums with slightly different initial conditions:
Trajectory of a double pendulum:
Real experiment of double pendulum trajectory (tracked with an LED):
Real experiment:
Interactive simulation of a double pendulum at this link.
Example of resonance - Tacoma Narrows Bridge collapse in 1940: