For decades, skiers slid down snow-covered hills on long rectangular planks. But in the mid-1990s companies began offering skis with an hourglass shape. They turned more easily because they concentrated the skier's weight at the middle of the ski's inside blade edge. The focus makes the ski less likely to slip out of the track that the blade carves as it traverses the inevitable microbumps of snow on any slope. Today "shaped" or "carving" skis dominate the market.
There's a subtle catch, however. The concentrated forces create a strong angular moment within the ski. To maintain structural integrity, the ski must be built with more rigidity. But that means the ski is apt to vibrate, which is annoying and can even lift it off the snow, causing a skier to wipe out.
This article was originally published with the title At the Moment.