Most research on virtual-touch technology, or haptics, has focused on giving people the sensation that they're feeling solid objects. Now researchers in Japan are developing ways to simulate the subtle feel of flowing water--­inching us closer to the day when ­virtual­-reality aficionados can enjoy the sensations of, say, rowing a boat or stirring a drink.

Representing flowing water requires churning through complex formulas that can slow a computer to a crawl. That's a problem for haptics, which uses tactile interfaces to provide physical resistance that simulates the "feel" of actions depicted on a computer screen. "The computation of the force field has to be completed and updated within 1/500 of a second," says ­Yoshinori Dobashi, an associate professor at Hokkaido University in Japan. "This is almost impossible." Dobashi and colleagues got around this problem by doing some of the math in advance. Working with prototype games that simulate kayaking and fishing, Dobashi and his team created a model that approximates real-world forces associated with different water velocities and different rod or paddle positions. Then they precalculated and saved numerical representations of these forces. During a game, sensations are conveyed to the player via interfaces created by Makoto Sato of the Tokyo Institute of Technology. For example, motor-driven wires pull on the ends of a paddle in the player's hand to simulate kayaking.