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From my local blog

My son is doing a science experiment for school and his chosen problem is "What has a greater effect on hitting a baseball for distance. Bat speed or bat weight?" In researching this for him, because I had to reach way back to my physics classes for this, I came across some great findings... Remember this when buying your equipment this year. From http://paws.kettering.edu/~drussell/bats-new/batw8.html

Bat Weight and Batted Ball Velocity

To see the effects of bat weight and bat speed, here is a summary of an experiment that I found summarized in a 1980 high-school textbook, Physics of Sports developed by Florida State University.[6] For this experiment, the ball mass, pitch speed, and bat swing speed were all kept constant. Only the bat mass was changed. The data shows that a heavier bat produces a faster batted ball speed. This makes intuitive sense since a heavier bat brings more momentum into the collision. Doubling the mass of the bat results in an increase of almost 12mph. So, using a heavier bat should result in faster hit balls, which means the hit ball will travel farther. If a player can maintain the same bat swing speed with a heavier bat, the heavier bat will produce higher batted ball velocity and an increase in distance. But, any player who has experimented swinging bats with widely different weights knows that it is easier to swing a light bat than a heavier bat. Put another way, it takes more effort to swing a heavy bat with the same speed as it does a lighter bat, and most players cannot swing a heavy bat as quickly as they can a bat which is half the weight. So, we need to see how the batted ball speed depends on bat swing speed.
Bat Weight Batted Ball Velocity
20oz (0.57kg) 68.5mph (30.6m/s)
25oz (0.71kg) 73.0mph (32.6m/s)
30oz (0.85kg) 76.2mph (34.0m/s)
35oz (0.99kg) 78.6mph (35.1m/s)
40oz (1.14kg) 80.4mph (35.9m/s)

Bat Swing Speed and Batted Ball Velocity

A similar experiment (from the same 1980 high-school textbook Physics of Sports developed by Florida State University[6]) changed the bat swing speed while the the ball mass, pitch speed, and bat mass (30oz) were all kept constant. The data shows that a faster bat swing produces a faster batted ball speed. Doubling the swing speed of the bat results in an increase of almost 22mph. So, it would seem that swinging the same bat faster is more beneficial than swinging a heavier bat at a the same speed. Ideally, the best result would be to swing a heavier bat faster. But, as I already stated, it is harder to swing a heavier bat with the same speed, let alone swing a heavier bat faster. So, it looks like we have two different effects (increasing bat weight and increasing bat swing speed) which both result in faster batted ball speeds. However, it does not seem possible to get both effects at the same time. In fact, increasing bat weight might decrease bat swing speed. So, we need to see how these two parameters are related before we can answer the question "what is the final batted ball speed?"
Bat Swing Speed Batted Ball Velocity
20.5mph (9.2m/s) 62.0mph (27.7m/s)
27.3mph (12.1m/s) 68.8mph (30.7m/s)
34.3mph (15.3m/s) 76.2mph (34.0m/s)
41.0mph (18.3m/s) 83.8mph (37.4m/s)
47.9mph (21.4m/s) 91.4mph (40.8m/s)

Bat Weight, Swing Speed, and Batted Ball Velocity

Anyone who has swung a bat knows that it is easier to swing a lighter bat than it is to swing a heavier bat. More importantly, it is possible to swing a lighter bat faster than a heavier bat. Exactly how the bat swing speed is related to bat weight for a given player is a little harder to determine. Terry Bahill[2,7,8] and his colleague have extensively studied the relationship between bat swing speeds and bat weights for a wide variety of players. Bahill developed the Bat ChooserTM machine to measure bat swing speed, and uses the results to determine the Ideal Bat WeightTM for an individual player. This device has been successfully used by numerous players who have greatly increased their batting averages after correctly choosing an appropriate weight bat, as well as by several college teams who have gone on to win championships after finding their correct bat weights. His data shows definitively that players cannot swing heavy bats as quickly as they can lighter bats, and the details vary somewhat from player to player and vary more considerably depending on the technical playing ability of the individual. Both plots show that the batted ball velocity initially increases as the bat weight increases until the bat swing speed drops below a certain level after which the batted velocity begins to decrease again. This results in an "optimum" bat weight for each player, indicated by the black arrows in the plots. This optimum bat weight is the bat weight which will result in the fasted batted ball velocity for each player. The optimum bat weight for the professional power hitter is about 41oz, and about 16oz for the Little Leaguer. Perhaps a pertinent question is why a major league power hitter would choose to use a lighter bat (say 32oz) when an optimal 41oz bat would produce a higher batted ball velocity? Two possibilities come to mind. First, the fact that you can swing a lighter bat faster means that you can wait just a little bit longer before committing to a swing. For a professional, the ability to wait even 1/10th of a second longer to watch a pitched ball can result in a considerable improvement in the chance of making contact. Secondly, most hitters can control a lighter bat more effectively than they can a heavier bat. Bat control affects the location of the bat as it crosses the plate, and more control over bat location is definitely a good thing when the pitched ball crosses the plate considerable variation in height or distance from the batter. Notice further, from the plot for the major league power hitter, that for bat weights in the range of 35oz to 45oz there is very minor change in the batted ball velocity. Using a 33oz bat instead of a 41oz bat will only very slightly reduce the batted ball velocity, but it will have a significant affect on the bat swing speed and the resulting swing time. Based on such a trade-off between ball speed and bat control, Bahill has defined the Ideal Bat WeightTM as the weight at which the batted ball speed drops 1% below the speed of the optimum batted ball speed bat weight. As shown in the plot, the Ideal Bat Weight for the power hitter is about 32-33oz. This is right in the weight range used by most professional players. The results for the Little League player are quite different. The optimum bat weight, for maximum batted ball speed, is about 16oz, and the Ideal Bat Weight is about 12-13oz. As was shown in the table at the top of this page, most available 30-inch wood and aluminum Little League bats weigh between 20 and 26oz, which is well above both the optimum and ideal weights for this player. From the plot we can see that if this player used a 23oz bat he would have a much lower bat swing speed and a significantly lower batted ball velocity. Most young players are forced to use bats which are heavier than the ideal bat weight because light enough bats are not available. Only this year (2003) have composite bats become available that begin to approach 16oz for a 30-inch bat.

Rules of Thumb for Recommended Bat Weights

The plots above were obtained by using the Bat ChooserTM machine to determine the Ideal Bat WeightTM for a specific player. The data proves the point that bat weight affects both swing speed and batted ball velocity. But, how does an amateur player, without access to this machine, estimate his/her optimum (or ideal) bat weight in order to get the best batted ball speed and still maintain control over the bat? Using the results of a large database of measurements* from the Bat Chooser instrument, Bahill and his colleagues have come up with up set of basic rules of thumb which can help any player estimate the recommended bat weight he or she should be using in order to obtain the highest performance possible. If you want more detailed rules, or information about how Bahill and his colleagues arrived at these rules of thumb I would strongly recommend reading his book.[8] (Note: For calculating bat weight from the formulas in the table, use height in inches, weight in pounds and age in years.) Conclusion: Reno Baseball and Sparks Baseball little leaguers should concentrate on lighter bats to increase bat speed and focus on their form.

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