Earthquake ball

I’m mesmerised by this YouTube video, which shows a massive counterweight suspended inside Taiwan’s Taipei 101, the world’s tallest building (for now) acting against the tremors felt from the Sichuan earthquake on May 12. I don’t quite understand the physics behind it, but the weight, which more or less stays still as the building sways around it, apparently dampens the effect of the movement. You’ll find an explanation from someone who knows what they’re talking about over at BLDGBLOG:

As earthquake waves pass up through the structure, the ball remains all but stationary; its inertia helps to counteract the movements of the building around it, thus “dampening” the earthquake.