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The science of baseball: a conversation

Today is the Cardinals' home opener against the Chicago Cubs.

For St. Louis Public Radio’s Véronique LaCapra, baseball season means it’s time to talk about the science behind America’s national pastime.

And Washington University aerospace engineer David Peters was happy to join in.

Here's a summary of their conversation, plus, some web extras for you.

PETERS: I'm a baseball fan from day one. I was at Stan Musial's last game here in St. Louis. Turns out I was in Cincinnati and happened to go to the game when Pete Rose broke Ty Cobb's record. I was at the game where Roger Maris' home run record was broken by Mark McGwire. I've just been a baseball fan, always have been.

LACAPRA: I can imagine that there’s a lot of physics involved in pitching. Can you talk about some of the main types of pitches — the curveball — the physics behind them?

PETERS: The basic principle's called the Bernoulli principle. And the Bernoulli principle says that when air speeds up, its pressure goes down, and when air slows down, its pressure goes up.

So the top of the ball is spinning towards the batter; the bottom of the ball is spinning away from the batter. So the top spinning towards the batter slows down the air on the top of the ball, and since the air slows down, the pressure goes up. The bottom of the ball is spinning away from the batter, actually speeds the air up.

So there's high pressure on the top, low pressure on the bottom, it pushes the ball down. Ball falls much faster than just gravity would make it. And they call it a 12-to-6 curve ball, 'cause it goes from 12 o'clock to 6 o'clock on the clock dial. You can't believe it. It's unmerciful.

Almost every pitch — fast ball, curve ball, knuckleball — they move because of air pressure. They move because of Bernoulli's principle and the different ways the pitcher makes them spin.

LACAPRA: And so what about the guy who’s on the receiving end of those 80 or 90 mile-an-hour pitches? How do you even focus on a ball coming at you that fast, let alone control where it’s going to go, or hit it out of the park?

PETERS: This is one of the incredible coincidences about baseball, or Abner Doubleday knew what he was doing, or something. It's 60 feet, 6 inches, from home plate to the pitcher's mound. Although the pitcher's leaning forward, so he's maybe 55 feet away when the ball comes. Ball going at 90 miles an hour is about 130 feet a second.

That takes about a half a second to get to the plate. The human reaction time is a half a second. If the pitcher's mound were 45 feet from home plate, nobody would ever get a hit, every game would be a no-hitter.

LACAPRA: Really?

PETERS: That's right. So this is the beauty of it, but it's right on the verge. So you have to have very good reflexes. You have to think. You have to have good eyes. A good batter can actually see the stitching on the ball and see it spinning, and can tell which way it's spinning, whether it's going to be a curve ball —

LACAPRA: Are you kidding me?

PETERS: I'm not kidding you at all. Still, it's barely time to make that decision. And it’s amazing, you can do it. People have said it’s the most difficult thing in sports, hitting this little round ball with a round bat, and making it go exactly where you want it to. But you can.

LACAPRA: So I have to ask: do ball players really think about all this science when they’re out on the field, or do they just do it without really understanding it?

PETERS: For a long time players just did it. But Ted Williams — Ted Williams was probably the greatest hitter of all time — he thought hitting was a science.

And he wrote a book on the science of hitting, and he actually analyzed it. And he learned several things in his studies. First, he learned that bat speed was the most important thing. Up until then, people used these huge heavy bats, like clubs, you know, Babe Ruth had a bat that was 42 ounces or something, you know. You can’t argue with Babe Ruth!

But Ted Williams decided that weight’s important, but speed was better. And so the bats have gotten lighter. And Ted Williams worked out these angles, and where you should move your elbow in, or move your elbow out, how to get the best angle of the bat on the ball, and he set out his goal to become the best hitter of all time and he really did.

LACAPRA: So science matters, even in baseball.

PETERS: Science matters. Science is everywhere.

WEB EXTRAS: More on the science of baseball from Washington University's David Peters. Click on each audio piece to hear Peters' answer:

Q: I’ve heard that lefties have an advantage in baseball. Is that true, and is there physics involved in that?


Q: Is it faster to slide into a base, or run to it, and why?


Q: One more thing — catching.