When Ryan Zimmerman stands at the plate, there’s no time to analyze physics. “I’m thinking about what the pitcher might throw in that situation,” says the 22-year-old rising star with the Washington Nationals. “I have to eliminate as many options as I can before he releases the ball.” Twenty times last season, Zimmerman pounded a pitch into the seats. Now PM stops the clock to examine ball spin, bat speed and the rest of what Zimmerman instinctively understands about hitting. Here’s how those home runs happened.

By Davin Coburn

Illustrations by Intoaroute

Photograph by Getty Images

Popular Mechanics; June 2007

A SUPERSIZE SWEET SPOT A bat vibrates at multiple frequencies when it collides with a ball. How much energy is transferred to the ball — instead of spread through the bat and the batter’s hands — depends on where the collision occurs. A bat vibrating at its fundamental frequency (above, in black) has a node of zero vibration about 6 1/2 in. from the barrel end (Node 1). This was long thought to be the bat’s sweet spot. But Rod Cross, a physicist at Australia’s University of Sydney, found that the spot is more like a zone. At a second frequency (in red), a bat has another node about 4 1/2 in. down the barrel (Node 2). Hits between the two produce minimal vibration — and transfer more energy — at both frequencies. "Every ball I’ve hit that I haven’t felt, I knew I hit well," Zimmerman says.

BAT SPEED VS. MASS Boosting two factors — the mass of the bat and the speed of the swing — can raise batted ball speed (BBS), which adds distance to a hit. But swing speed can affect BBS more dramatically.

Research has shown that doubling the weight of a 20-ounce wood bat can raise a BBS of 68.5 mph to 80.4 mph — a 17.3 percent increase. But Daniel Russell, a professor at Kettering University in Michigan, found that doubling the swing speed of a 30-ounce bat can raise a BBS of 62 mph to 83.8 mph — a 35.1 percent increase.

In terms of turning a hit into a homer: Against a 94-mph fastball, every 1-mph increase in swing speed extends distance about 8 ft.

THE IDEAL BAT University of Arizona professor Terry Bahill found that the maximum bat weight before swing speed drops is about 41 ounces. But a pro player’s ideal bat weight, he says, is lighter — in the 31- to 32-ounce range. This weight produces a BBS 1 percent below the BBS of the maximum-weight bat — allowing the batter greater maneuverability with a negligible loss of power.

Zimmerman has discovered the same principle with his 34-in., 32ounce MaxBat. “A bigger bat obviously has more solid wood,” he says, “but you can handle a smaller bat better.”

THINKING QUICKLY A 90-mph fastball can reach home plate in 400 milliseconds — or four-tenths of a second. But a batter has just a quarter-second to identify the pitch, decide whether to swing, and start the process. “Once the pitch is in flight, it’s the snap of your fingers,” Zimmer-man says. What happens next is “pretty much just instinct.” A batter takes 100 milliseconds to see the 3-in. ball, and 75 milliseconds to identify spin, speed and pitch location. The batter has another 50 milliseconds to decide whether to swing, and where, before he must act. It can take nearly 25 milliseconds for the brain’s signals to pulse through the hitter’s body and start his legs moving. The swing itself takes 150 milliseconds.

SPIN CONTROL A fastball comes to the plate with backspin — up to 1800 rpm. To hit the ball out of the park, a batter must reverse the rotation of the ball so that it leaves the bat with backspin. This gives the ball lift.

A curveball can carry topspin of 1900 rpm, making it bite downward as it crosses the plate. By crushing a curve, a batter builds on the pitcher’s topspin — producing 45 percent more backspin off the bat.

The result? Curveballs can be hit farther. Mont Hubbard of the University of California, Davis, found that a 94-mph fastball leaves the bat 3 mph faster than a 78-mph curveball — but it travels 442 ft. compared to the curve’s 455 ft.

FORCING THE ISSUE Major League baseballs have an average mass of 5.125 ounces, and a 90-mph fastball can leave the bat at 110 mph. Extrapolating Newton’s second law of motion, Russell determined that, in a collision lasting less than one-thousandth of a second, the average pro swing imparts 4145 pounds of force to the ball. Peak forces exceed 8300 pounds — enough to stop a Mini Cooper, rolling at 10 mph, in its tracks.

MAXING OUT Contrary to the lore surrounding historic, titanic blasts — like Mickey Mantle’s fabled 565-ft. shot in 1953 — physicists estimate the farthest a man can hit a ball, at sea level, without help from the wind, is about 475 ft.

For the first 50 milliseconds of a swing, a batter can stop his 2-pound bat in time to check the swing. By 110 milliseconds, the bat, moving at up to 80 mph, carries too much inertia to be stopped.