Less lively aluminum baseball bats change game
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(HealthNewsDigest.com) – Baseball is considered relatively safe, but its reputation was established in the era of wooden bats. Aluminum bats, introduced in the 1970s, had an enormous “trampoline effect” and made the game more dangerous.
The Not So Sweet spot on the BBCOR aluminum bat
A 90-mph pitch could come off a lively aluminum bat at 108 mph and reach the pitcher 0.375 seconds later, leaving him no time to react when the ball was hit right back at him.
In fact, several high school players were severely injured and at least two killed by scorching line drives.
In 2003, 18-year-old Brandon Patch was killed by a line drive when he was pitching for his team in Montana. In 2009, his family won a verdict against the maker of the Louisville slugger for his death.
In 2010, a 13-year-old Vermont pitcher also was killed by a line drive.
Last year, the National Collegiate Athletic Association required all aluminum bats used in college play to meet a new performance standard designed to limit the exit speed of the ball off the bat. This year, the National Federation of State High School Associations also has implemented the new standard.
With spring training beginning at all levels this month, David A. Peters, PhD, the McDonnell Douglas Professor of Engineering in the Department of Mechanical Engineering & Materials Science at Washington University in St. Louis, explains the new standard.
WUSTL baseball head coach Steve Duncan, and WUSTL hitting coach and Rawlings category manager for bats Kyle Murphy also comment on the new bats and how they have affected play.
First the balls
Peters, an avid baseball fan, has made 32 video vignettes about the physics of baseball for Cardinal Nation, the St. Louis Cardinals fan club.
“Three things come into play when a baseball comes off a bat,” Peters says. “The speed of the balls coming in; the speed the bat’s being swung – the speed of the bat hit; and then how much energy is lost in that collision.”
The energy lost in the collision depends on how bouncy the ball is and how springy the bat. That bounciness, or springiness, is technically known as the coefficient of restitution, a measure of how much energy the ball or bat gives back after being deformed by an impact.
As a general rule, wood bats made of white ash, the traditional material, give very little and store little energy. But what little they store they give back efficiently. The ball, on the other hand, distorts a lot under impact but is relatively inefficient in giving it back, losing the kinetic energy as heat. This is why a game played with wood bats is relatively safe.
But players are always trying to figure an angle, Peters says.
In the early days of the game, it was often the ball that was “cooked” or “juiced,” so in the late 1960s a standard was introduced to limit variations among balls.
The rule is that a ball shot from an air cannon at 85 feet per second at a wall of northern white ash must rebound with a speed of 54.6 [plus or minus symbol] 3.2 percent of the initial speed.
That gives it a coefficient of restitution of about 0.5, meaning the ball loses in the impact roughly half the energy it had coming in.
In contrast, a golf ball is much bouncier; it has a coefficient of restitution of about 0.78.
Then the bats
Hot bats became an issue when aluminum bats were introduced in the 1970s. Because aluminum bats are lighter, they can be swung faster than a wooden bat, and that made the balls come off faster.
The big difference between the wooden and aluminum bats, however, was again the coefficient of restitution, called the trampoline effect in the case of the bats.
The hollow aluminum bats flex more when they’re hit and allow the bat to stay in contact for a longer time, imparting more energy to the ball.
Peters says we’ve all seen the difference this makes in the sport of pole vaulting. The poles, like the bats, were originally made of ash but are now made of tubular aluminum.
“The old poles were rigid,” he says, “but now the pole bends halfway down and springs back, flipping the vaulter over the bar.
“Aluminum bats can be engineered to have any amount of rebound one wants by designing the thickness and shape distribution of the bat,” he says.
In fact, after the introduction of aluminum bats, bat designers went a bit overboard. Bats made of titanium, for example, had such an enormous trampoline effect that they were quickly banned.
Another troublesome design that resulted in law suits was the “Air Attack” bat made by Louisville Slugger. It has a pressurized bladder inside that compresses on impact and then expands fast enough to help propel the ball.
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