From the time a baseball leaves a pitcher's hand to its arrival at the bat, about one-half second elapses, according to Porter Johnson, a retired physics professor and the creator of the website, "The Physics of Baseball." A proper hit strikes the baseball with the sweet spot of the bat, an area only 1 square cm in size. Only about one-hundredth of a second in timing separates a hit and a foul. The combination of all forces involved determines the speed of the struck ball.
History
In the early years of professional baseball, home run hitters like Babe Ruth and George Sisler favored heavy baseball bats ranging from 42 to 54 oz. Some players even weighted bats by driving nails or phonograph needles into the wood, believing that heavier bats knocked the ball a greater distance. Since ball speed depends on the speed of the swing, as well as the mass of the bat, professional hitters later shifted to lighter and faster bats. Today's bats typically weigh between 31 and 35 oz. Although hit distance drops compared with the heavier bats, today's lighter bats offer more control.
Considerations
Ideally, when a swung baseball bat strikes a thrown baseball, the struck ball's speed equals the speed of the swing plus the speed of the pitch. In the real world, many other factors reduce this speed. The baseball distorts slightly on impact, absorbing some of the force of the strike. Efficiency of transfer of momentum depends upon hitting the ball with the bat's center of mass, or sweet spot. A hit outside the sweet spot expends energy through vibration of the bat. Hits above or below the sweet spot put some of the force into ball spin instead of speed.
Size
Physics calculations show that the best weight for a bat in terms of energy transfer is between 15 oz. and 18 oz.--about half the weight of a modern baseball bat. Finding the best bat weight depends on the capability of the player. Keeping the bat heavier adds velocity to the ball, and so does swinging faster. Players strong enough to swing a heavier bat benefit from the extra weight.
Types
Today's players choose between wooden bats and aluminum bats, both of which produce different average ball speeds. The National Collegiate Athletic Association determined that the standard 34-inch wooden bat, when swung at 66 mph against a ball traveling at 70 mph, resulted in a ball speed of 97 mph. Different types of hardwood and the speed and strength of players shifted that speed to above 110 mph. Metal bats could add another 5 mph to 10 mph of ball speed because of the trampoline effect, or the compression and rebound of the metal bat.
Misconceptions
Estimates of maximum batted-ball speed when hit by high performance metal bats range as high as 123 mph, according to Daniel Russell, professor of applied physics at Kettering University and creator of the website, "Physics and Acoustics of Baseball & Softball Bats." Metal bats meeting standards set by the NCAA and National Federation of State High School Associations in 1999 drop that maximum speed to only 5 mph faster than the 110-mph upper level for wooden bats. Exceptional players might exceed that batted-ball speed slightly.
References
- Daniel A. Russell, Ph.D.: Bat Weight, Swing Speed and Ball Velocity
- Daniel A. Russell, Ph.D.: Should Metal Baseball Bats Be Banned Because They are Inherently Dangerous?
- Porter W. Johnson, Illinois Institute of Technology : The Physics of Baseball
- American Journal of Physics: Dynamics of the Baseball--Bat Collision
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