Near the top of Taipei 101, a 508-metre skyscraper in Taiwan, a 660-tonne steel ball hangs from steel cables like a pendulum.
When the tower sways in a typhoon or earthquake, the heavy ball is slow to start moving. So it lags behind, swinging against the sway, and pulls the building back through the cables.
Shock absorbers beneath it soak up the swinging. Taipei 101 says this cuts the tower's movement by up to 40%.