more on the grip ….4


Figure 15 from Alan Nathan’s paper showing the velocity response as a function of time for a point on the handle of the bat 13cm from the knob due to an impact in the barrel (68cm from the knob). The arrow indicates the time at which the collision is over – the change in momentum of the ball is 99% complete. Notice that the handle has just barely begun to move by the time the collision between bat and ball is complete

Alan Nathan has developed an elegant computational model of the bat-ball collision that supports the idea that the collision between bat and ball is over before any information about the handle end of the bat is available to the ball. Nathan differentiates between the collision time, during which 99% of the impulse is delivered to the ball to change its direction and speed, and the contact time which is the total time the bat and ball are in contact with each other. Because of hysteresis effects in the ball it is possible for the ball to be in contact with the bat even though no forces are being exerted on the ball. Based on experimental data, Nathan calculates uses a incoming ball speed of 67 m/s to obtain an approximate contact time of 1.1 ms with a shorter collision time of 0.6 ms. His computational model allows him to analyze the vibrational behavior of the bat during and after the collision, and he was able to show that under realistic playing conditions the collision time between bat and ball is long over before any information from the handle end of the bat is available to alter the collision. The figure at right shows the velocity response (as a function of time) of the handle of the bat after an impact on the barrel. The arrow identifies the time at which 99% of the impulse has been delivered to the ball. The plot shows that the handle is only just beginning to respond to the impact by the time the collision is over. I have measured similar response plots in my laboratory and the propagation time – the time it takes for a vibrational impulse to travel from the impact location to the handle and back again – is longer than the impact duration. This means that there is not possible for the way in which the handle is gripped to influence the final ball speed since the ball has already left the bat before it even knows the handle exists. As far as the ball is concerned, it has just impacted an infinitely long bat with no ends (with the same inertial properties as the real bat, of course). Only for impacts very close to the handle can the manner of gripping possibly affect the resulting batted-ball speed.

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Wonder, silence, gratitude

one who is going upstream ......

SS24 - in search of the bull !

one who is going upstream ......

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