How Mass Dampers Stop Structures from Shaking

Being atop a skyscraper when it sways is disconcerting, but not as terrifying as that sway would be if it weren't for mass dampers. That idea comforted me a little while atop the World Trade Center and the Empire State Building, but I never understood how they work until today. This simple but thorough explanation of the science from Minute Physics uses a LEGO Saturn 5 rocket, or two of them, to show how a mass damper works. The video is really only 3:40; after that, it's an ad. (via Geeks Are Sexy)