On Sunday, my Washington Redskins defeated the archrival Dallas Cowboys. It was a huge victory for coach Mike Shanahan and quarterback Donovan McNabb, both in their first game as a Skin, and also for long-suffering fans. Some are already talking about a turnaround season for the team, perhaps even a championship. Does this key win give the Redskins momentum? Here is an excerpt from my new book, On Second Thought: Outsmarting Your Mind's Hard-Wired Habits, which devotes a chapter to psychological momentum, especially in sports:

"Our naïve sense of the physical world-and impersonal forces like speed and momentum-may carry over directly to the psychological world. Sports fans in particular will swear to the validity of momentum in athletic contests, both individual momentum and team momentum. Players-for reasons not fully understood-will suddenly go "on a roll," or they'll get a "hot hand." Or they'll just as suddenly lose their momentum, and the contest will shift in an opponent's favor.

Is this just magical thinking, or is there something to the idea that psychological momentum affects performance? Psychologists have begun to study the link between naïve physics, the "propensity effect," and actual attitudes and beliefs, with some interesting results. Indeed, psychologists have begun work on a unifying theory of psychological momentum that begins with the basic laws of Newtonian physics.

Newtonian physics says that momentum equals velocity times mass. It's simple. But what does this mean in the realm of human motivation and performance? Well, according to these theorists, psychological velocity is provided by some important event; in sports that is usually a "big play" that turns the tide: a key interception in a football game or a steal and slam dunk in hoops.

Mass, according to this theory, is provided by the social context: How important is the game? Is a team emotionally invested in the outcome of this game more than others? In Washington Redskins country, that game is indisputably the home game against the Dallas Cowboys: It's a major topic of conversation not only on Sunday but for the entire "Dallas Week" leading up to the game. According to psychologists, this qualifies as mass, which combines with velocity to produce momentum.

Let's look at the experiments. In one study, Ohio University psychologists Keith Markman and Corey Guenther recruited a group of knowledgeable basketball fans and had them view a film clip from an actual basketball game, a 1998 contest between Duke University and the University of North Carolina. The Redskins-Cowboys rivalry pales next to this college rivalry between the Duke Blue Devils and the Carolina Tarheels, and in 1998 the Devils were ranked #1 in the country and the Tarheels #2.

In the 10-minute film clip used for the experiment, the Blue Devils ran off 15 unanswered points, although they trailed the Tarheels during the entire segment. Duke ended up losing the game to North Carolina, 97-73, but the study volunteers didn't know this (and interviews revealed than none of them recalled this game). The psychologists stopped the film every minute and asked the fans these two questions: Who has the momentum now? Which team do you believe will win the game? After viewing the film clip, they were asked what specific event during the game was most important in shifting the momentum of the game.

When they crunched the data, the psychologists found some confirmation for their notion of psychological momentum. Most of the "fans" perceived that Duke had momentum during the game, and most predicted that Duke would go on to win. When asked, the volunteers named a technical foul against one Carolina player-or a key rebound and three-pointer by a Duke player-as the turning point that gave Duke the momentum.

Markman and Guenther wanted to further explore the analogy between physics and psychology, including the idea of mass. Remember that mass, in the psychological sense, is the emotional importance of an event. In a second experiment, they had volunteers read a description of a hypothetical basketball involving a team called East Midland, a very competitive squad in their league. Some volunteers read a scenario in which East Midland played Millersville, another team in their division. Others read a scenario in which East Midland played West Midland, a cross-town team with whom they have had an intense 90-year rivalry. In both scenarios, East Midland wins a hard-fought game and is going on to play Conner for a playoff spot.

Which East Midland team has the greater momentum going into the game against Conner? This is the question the psychologists asked the volunteers. And they found what their theory predicts: Fans believe that a win against a long-time rival would give east Midland more momentum than a more neutral win, even though both are just as important in the standings. This lends support to the idea that "mass," in the form of emotional importance, contributes to psychological momentum."

By my reckoning, this means the Skins are heading to the NFC Conference title!