Home runs

It’s World Series time again, and it’s shaping up to be an exciting one–but for me, nothing can equal the excitement of the 1909 Series.

I remember it like it was yesterday. The smell of the grass, the roar of the crowd, as I made my way to the mound to start for the Detroit Tigers…

What’s that? I’m too young to have pitched in the 1909 World Series? Well, I dare you to look it up. 1909. Detroit Tigers. Ed Willett.

See? I’m older than I look.

The game has changed a lot since then, but it’s still a duel between pitcher and batter, a duel the pitcher usually wins (which is why a .333 batting average–meaning the player failed two out of three times at bat!–is considered pretty good).

Something else that hasn’t changed is that nothing gets the crowd on its feet like a home run. That’s because they’re so excited by the fascinating physics involved–physics outlined in an article by Noel Wanner that I came across on the World Wide Web site of San Francisco’s Exploratorium, the granddaddy of all science centres.

Here’s the gist of it:

Several factors determine the outcome of a hit. One is the air density. To travel through the air, a ball has to push air molecules out of the way. That takes energy. (In a vacuum, a 400-foot home run would travel twice as far.) The more densely packed those molecules, the more energy it takes.

Air density changes with temperature, air pressure and humidity. Hot air is less dense than cold air: 36-degree Celsius air is 12 percent less dense than zero-degree air. Air pressure varies with altitude, dropping about three percent for every thousand feet of elevation–which means a baseball hit in Denver experiences 15 percent less drag than a baseball hit in Boston. And humid air is less dense than dry air, because the water molecules in it weigh less than the oxygen and nitrogen molecules they displace. Air at 80 percent humidity is one percent less dense than dry air. Even one percent is significant, because just a five percent difference in drag can change a fly ball into a home run–or vice versa.

Another factor in the outcome of a hit is where the ball hits the bat. Every bat has a “center of percussion” (better known as the “sweet spot”), generally located around the maker’s label. If you hit the ball there, you don’t feel any wobbling or twisting of the bat. Miss the sweet spot, and you’re more likely to have a weak hit.

The angle at which the bat hits the ball is also important. A dead-center hit produces a line drive. If the bat hits the ball a few millimeters above center, it drives the ball down, if it hits a few millimeters below center, the ball will fly up. That could produce a home run or just an an easily caught fly. The difference between the two is distance, which is largely determined by how fast the ball travels after it’s hit.

Both the bat and the ball have momentum, calculated by multiplying mass times speed. The more momentum an moving object has, the more energy it takes to change its direction. The 30-ounce bat has more momentum than the five-ounce ball, so when the two hit, the bat continues on its way, while the ball stops, then accelerates away in an entirely new direction.

Theoretically, a heavy bat should send the ball faster and farther. However, a heavy bat takes longer to get up to speed, and therefore requires not only greater strength but faster reflexes on the part of the batter. Many hitters prefer lighter bats, which they can swing faster.

How fast the ball was pitched also figures into the outcome. Baseballs are very elastic: in scientific terms, they have a high “coefficient of restitution.” That means that after they’re squashed on impact, they spring back into shape, using most of the energy imparted by the pitcher to zip off in an entirely new direction. (A little energy is lost as heat.)

With so many factors having to be just right, it’s amazing there are as many home runs as there are. Baseball fans should be grateful that baseball changed the ball in 1920 to make it livelier and encourage more power hitting.

It makes it harder on the pitcher, though. Sure am glad I retired in 1915.

Permanent link to this article: https://edwardwillett.com/1997/10/home-runs/

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