Physics and Acoustics of Baseball & Softball Bats Daniel A. Russell, Ph.D. Graduate Program in Acoustics The Pennsylvania State University The contents of this page are ©2003-2011 Daniel A. Russell

# What Happens when Ball Meets Bat?

## Baseball Impacting a Baseball Bat

The movies below were extracted from high speed camera recordings of the impact between a baseball shot out of a cannon and a stationary baseball bat barrel segment made from composite materials. The difference between the movies is a factor of two in the initial ball speed prior to to the collision (movie on the right has the faster ball).

These movies are owned by CE Composites Baseball (combatbaseball.com), designers and manufacturers of composite baseball bats,
Ottawa, Ontario, Canada, and are shown here with their permission.

Observing the movies we can notice that......
1. The ball experiences a significant amount of deformation during the collision, much more so than the bat. By comparing the two movies we can also see that the amount of deformation is noticeably larger for the faster incoming ball speed.
2. The speed of the ball is considerably less after the collision than it was before the collision. This effect is usually measured as the coefficient of restitution (COR), which is the ratio of incoming velocity to outgoing velocity. Research has shown that the COR roughly decreases linearly with increasing ball velocity.
The movie below shows a baseball impacting a metal baseball bat barrel at approximately 100mph. This movie clearly shows that the bat undergoes some compression during the collision. It is a little hard to tell from this movie, but the barrel appears to show both flexing along its length and some compression of the cylinder as well.

This movie is owned by CE Composites Baseball (combatbaseball.com),
designers and manufacturers of composite baseball bats,
Ottawa, Ontario, Canada, and are shown here with their permission.

## Softball Impacting a Softball Bat

The two movies below show the impact between a softball, with an initial velocity of approximately 90mph, impacting a stationary softball bat barrel segment.

These movies are owned by CE Composites Baseball (combatbaseball.com), designers and manufacturers of composite baseball bats,
Ottawa, Ontario, Canada, and are shown here with their permission.

Watching the movies (and comparing with the baseball movies above) we can notice several things:
1. The contact time between the softball and softball bat is longer than it is for a baseball (hardball) and bat. (a little less than two frames of the movie).
2. A softballs experiences an amazing amount of deformation during the collision, much more than the baseballs in the above movies. The amount of deformation is even more astounding when you consider how "hard" a softball feels when you hold it in your hands. The movies also show that, as was the case for the baseballs above, the softball is compressed (deformed) much more than the bat is. Furthermore the softball does not spring back to its original shape immediately after the collision with the bat. In fact, both movies show that the softball is still significantly deformed several milliseconds after the ball has separated from the bat.
3. As was the case for the baseballs, the speed of the softball is considerably less after the collision than it was before the collision. A significant portion of the initial kinetic energy was lost to friction forces during the compression and relaxation of the ball while is distorts during impact.
4. In this experimental setup the bat was simply supported at each end (which is different from the boundary conditions for a hand held bat). During the collision the bat flexes (bends slightly) and after the collision the bat oscillates back and forth indicating that some of the initial kinetic energy of the ball was transferred to vibrational energy in the bat.
5. During the collision the barrel of the bat compresses and expands, appearing to throw the ball away. This phenomenon is unique to hollow (metal and composite) bats and gives rise to what is called the "trampoline effect". In the two movies below I've isolated the two frames which show the barrel compression/expansion during the collision.

These movies are owned by CE Composites Baseball (combatbaseball.com), designers and manufacturers of composite baseball bats,
Ottawa, Ontario, Canada, and are shown here with their permission.

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