Health & Science

The fastest way to the base

Contrary to conventional baseball wisdom, a physicist says, the fastest way to reach a base is through a headfirst slide. On close plays, many modern players try to beat a throw by launching themselves headfirst into the air, landing on their bellies, and touching the base with an outstretched hand. Managers discourage these slides, insisting that the classic, feet-first slides on one’s butt are more efficient, and less likely to cause hand or head injuries. But Washington University physicist David Peters says the modern players are right. “It’s basic, fundamental angular momentum,’’ he says. As a player is running toward a base, his center of gravity is in the upper half of his body. When he slides headfirst, he pushes off with his legs and thrusts his center of gravity forward and downward toward the bag. But when a baserunner slides feet-first, he needs to rock his center of gravity backward and upward, disrupting his forward momentum—costing him a crucial millisecond. Though statisticians have been unable to confirm this hypothesis in real-game situations, retired stolen-base champion Rickey Henderson agrees with Peters. If you slide “when you’re running straight up,’’ he tells SI.com, “then you have a long distance to get to the ground. But the closer you get to the ground the less time it will take.’’

AIDS in the 19th century?

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The first human case of AIDS didn’t occur in the 1970s—or even in the 20th century. The first infection with HIV, says new research, may have taken place as early as 1884, nearly a century before HIV and AIDS were recognized by the medical community. “The virus was circulating under our radar even longer than we knew,’’ says Michael Worobey of the University of Arizona. Researchers believe that humans first acquired HIV from chimpanzees in Africa—probably while butchering the simians for meat. In examining blood samples of sick people in Africa going back decades, researchers have found proof of HIV in humans as far back as 1959. Worobey compared differing strains of the fast-mutating virus in these old samples, and then “ran the clock backward’’ by calculating how long it would take for these strains to have sprung from a common ancestor. The answer—an estimate—is 1884. The virus only infected isolated individuals for decades, Worobey believes, until newly urbanized African trade hubs in the 1950s brought masses of people from the bush into the cities, where it began to spread through sexual activity. The first time an infected person walked into a larger city like Kinshasa, Congo, Worobey tells Discovery News, it was “the spark arriving in the tinderbox.”

Snow over Mars

The Mars lander aimed its laser eye at the sky last week and saw something scientists never expected to see over the Red Planet: snowflakes. Two and a half miles above the Mars surface, snow was falling from the clouds. Researchers now believe that Mars winters regularly feature light snowfall. “Nothing like this view has ever been seen on Mars,’’ Canadian scientist Jim Whiteway tells The Washington Post. “What this is telling us is that water does rise from the ground to the atmosphere and then precipitates down.’’ The evidence that there is a hydrological cycle on Mars suggests that when the planet’s polar regions were warmer, they may have had rain, and could have nurtured life, says Peter Smith of the University of Arizona. “Is this a habitable zone on Mars? I think we are approaching this hypothesis.”

The Facebook narcissist test

Facebook profiles reveal more about your friends than they realize. In addition to telling you a person’s favorite band and romantic status, online profiles can also reveal whether he or she is a narcissist. Narcissism is a personality disorder characterized by intense self-absorption. Narcissists don’t really value other people, seeing them purely as a tool to serve their own needs. Researchers at the University of Georgia who studied Facebook profiles found telltale signs of narcissism in a small but significant portion of them. Instead of a snapshot, narcissists often feature a glamour shot or a professional photo. They tend to have large numbers of online friends and plenty of back-and-forth wall posts, but few truly intimate friends. In this way, a narcissist’s Facebook presence mirrors his real social life, says study author W. Keith Campbell. It “turns out that narcissists are using Facebook the same way they use their other relationships—for self-promotion, with an emphasis on quantity over quality.’’ Beware of such “friends,’’ Campbell tells LiveScience.com, because it’s ultimately unrewarding to be involved with people who love themselves too much. “Narcissists might initially be seen as charming, but they end up using people for their own advantage. They hurt the people around them and they hurt themselves in the long run.’’