I experienced the negative impact of this during a large project at a drywall plant. Large fans causing enough vibration and noise to disturb the residential area down the road from the plant. This was, of course, an engineering error 🫢, and cost a lot of money and time to fix. I learned a lot from that expensive mistake. Thanks for the video!
At the end of the video the driving force was slightly off the resonance. The amplitude experiences the beating with a frequency equal to the frequency mismatch. Not sure this phenomenon could be visually explained without oscillation equations.
Maybe the magnet at the end of the pendulum is affecting the current driving the electromagnets, inducing some other wave which shifts in and out of phase with the pendulum, causing the effect the electromagnets have on the pendulum to waver in strength.
