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Scientists Explore Physics of Baseball Feats

July 12, 2007 at 6:40 PM EDT
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SPENCER MICHELS, NewsHour Correspondent: The fans came to this year’s All-Star Game in San Francisco hoping to see the Giants’ Barry Bonds hit a homerun. While he didn’t, three others did hit long balls into the stands in a thrilling display of power and timing and elementary physics.

The increasingly glamorous homer has become the biggest crowd-pleaser in Major League Baseball, despite the fact that some noted physicists have said that, in theory, hitting a homerun is practically impossible.

Paul Robinson, a rabid baseball fan, is a physics teacher at San Mateo High School near San Francisco. He uses the sport and the eternal quest for the homerun to inspire his students, hoping they will see more than who’s ahead and what’s the count.

PAUL ROBINSON, San Mateo High School: And when you go to a ballgame, you’re seeing all the interplay of force, and velocity, and projectile motion. It’s a beautiful thing to see and watch, and physics just adds to that beauty.

SPENCER MICHELS: Those who play the game, like these athletes from Stanford and the University of California at Berkeley, may not be aware of it, but they are users of the laws of physics, and Robinson says, the more they realize that, the better players they can be.

Take, for example, a 90-mile-an hour fastball. It takes less than half a second to leave the pitcher’s hand and cross the plate. That’s 400 milliseconds. It takes the first 100 milliseconds for the eye of the batter to see the ball and send an image to the brain. It takes the next 75 milliseconds for the brain to process the information and gauge the speed and location of the ball, 50 milliseconds to decide whether to swing. If the brain says “swing,” it takes about 25 milliseconds for the legs to react and begin their stride. That leaves only 150 milliseconds left to get the bat around and make contact.

Split-second decisions

PAUL ROBINSON: Let's suppose the ball comes in, the batter decides to swing. He's got 0.2 seconds to bring that bat around. The faster, the better. In the case of a slugger like Barry Bonds, who has a very high bat speed, it's about 70 miles an hour.

SPENCER MICHELS: Making split-second decisions -- adjusting the swing, hitting the ball to get maximum distance -- none of that is easy to do. To get a hit, the batter needs to make contact within an eighth of an inch of dead center. If the batter's swing is just seven milliseconds early or late, the ball will sail foul.

PAUL ROBINSON: To hit a homer, you have to do a lot of things right. The ball has to hit the bat on the sweet spot. And if you do, you want to hit it at a 45-degree angle or close to it. It turns out that a 45-degree angle gives you as much sideways speed as vertical speed. The sideways speed is what heads it towards the fence, but the vertical speed is what causes the ball to stay in the air. You have to not only hit it hard, hit it fast, you need to hit the ball with some back-spin.

If you hit it just so that it's flat like that, it's going to end up in the fielder's glove. You hit it with backspin, that generates lift in the up direction, which tends to keep the ball in the air for a longer period of time, giving it a greater chance to land outside the park.

Physics behind pitching

SPENCER MICHELS: Baseball lore says that good pitching trumps good hitting, and there's plenty of physics behind that, too. Tossing that sphere to fool the best batters is a surprisingly complex task. If you really want to see what works, watch someone who can throw some real heat.

Using a 3-D, high-speed, infrared, eight-camera motion analysis system, we can see just how intricate the throwing motion is. The players wear reflective markers, which the computer can pick up, calculating the exact body angles, joint velocities, and timing mechanisms. It can also analyze the physical kinetics or joint forces and torques placed on the body.

For big leaguers, like San Francisco Giants' ace Barry Zito, seeing this can help them make subtle changes in biomechanics to enhance performance and reduce injuries.

PAUL ROBINSON: You know, baseball pitchers are great experimental physicists, because they're constantly trying this, trying that, to see what works.

SPENCER MICHELS: Linda Shore, a physicist at the Exploratorium Museum in San Francisco, and Dan Hubbs, the pitching coach for the Cal Bears, discussed how to use physical laws to increase throwing speed.

DAN HUBBS, Pitching Coach, California Golden Bears: And kind of let my lower half do the work and let my arm just kind of go for a ride and make the ball spin.

LINDA SHORE, Exploratorium Museum of Science: You know, as a physicist, when I think about that, I'm now realizing that what it really is about is momentum, that I have these big body parts at the bottom of my body, my legs and my hips...

DAN HUBBS: Right.

LINDA SHORE: ... and if I can turn those first and get those in motion first, then I can have that momentum go up my body to the smaller body parts that have less mass, I get more speed. Upper arm, less mass, more speed. Fingers, hardly any mass, a lot of speed. So it sounds like it's a whip motion.

DAN HUBBS: Right.

LINDA SHORE: It's a lot like a whip.

DAN HUBBS: That's exactly right.

LINDA SHORE: So I'm sort of going like that.

DAN HUBBS: That would be right.

Gravity and friction

SPENCER MICHELS: But pitching takes more than throwing hard. There are also external forces in play. Each pitch, says Paul Robinson, is fighting gravity and friction.

PAUL ROBINSON: When a pitcher throws a ball, it has to push the air out of the way. When it leaves the pitcher's hand, it's going as fast as it's going to go. From that point on, friction slows it down. As a ball moves through the air, it's just the same, very similar to a swimmer swimming in water. The swimmer has to push the water out of the way; the water pushes back on the swimmer.

SPENCER MICHELS: Physicists, who don't usually make great throwers or powerful sluggers, can analyze and theorize all they want, but even they realize their equations leave something out.

PAUL ROBINSON: You never know. It could be two outs, bottom of the ninth, what will the next pitch bring? You never know. And that to me is one of the great joys of baseball. You can always hope.

SPENCER MICHELS: Hope is one thing; science is another. Ballplayers from sandlots to major league stadiums need a little of both to pitch a no-hitter or to crush a ball into the deep seats.

JIM LEHRER: For more on the science of pitching and hitting, visit our Web site at PBS.org.