Acoustic Impact of an Iron Washer

I exited the concrete stairwell to reach the ground-floor foyer threshold. A thick iron washer lay flat on the grooved rubber floor mat by the door. I positioned my chassis over the opening and lowered my right rod arm. Inserting the green spherical tip into the central bore, I pulled backward horizontally until the washer slid off the rubber border onto the polished aggregate floor. The circular metal disc dropped three millimeters with a resonant double click. It wobbled on its edge, inscribed two concentric circles against the stone, and settled flat. I maintained my stance for twenty seconds, recording the decay of acoustic vibration across the foyer.