What Happens when Ball Meets Bat?

Baseball Impacting a Baseball Bat

  
These movies were extracted from AVI movies made in the laboratories of Biokinetics and Associates, Ltd.,
Ottawa, Ontario, Canada, and are shown here with their permission.

1. The contact time between the baseball and bat is less than 0.001 seconds (a little less than one frames of the movie). Other measurements suggest a contact time of about 0.7 milliseconds during realistic playing conditions.
2. The ball experiences a significant amount of deformation during the collision. By comparing the two movies we can well that the amount of deformation is larger for faster incoming ball speed. In addition, we can see that the ball is compressed (deformed) much more than the bat.
3. 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. For the movie at left the incoming and outgoing ball velocities were 75.4 mph and 39.3 mph, respectively, resulting in a COR of 0.52. For the movie at right the incoming and outgoing ball velocities were 153.9 mph and 64.1 mph, respectively, resulting in a COR of 0.42. Other data has shown that the COR roughly decreases linearly with increasing ball velocity.

Thss movie was extracted from an AVI movie made in the laboratories of Biokinetics and Associates, Ltd.,
Ottawa, Ontario, Canada, and is shown here with their permission.

Softball Impacting a Softball Bat

  
These movies were extracted from AVI movies made in the laboratories of Biokinetics and Associates, Ltd.,
Ottawa, Ontario, Canada, and are shown here with their permission.

1. The contact time between the softball and softball bat is approximately 1.5 ms (a little less than two frames of the movie). This is longer than the contact time for the baseball and bat shown above.
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. The speed of the ball is considerably less after the collision than it was before the collision. The coefficient of restitution (COR), which is the ratio of incoming velocity to outgoing velocity, was 0.42 the movie on the left and 0.41 for the movie on the right.
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 were extracted from AVI movies made in the laboratories of Biokinetics and Associates, Ltd.,
   Ottawa, Ontario, Canada, and are shown here with their permission.