Kansas State University Biomechanics Center of Percussion & the sweet spot • Earlier studies indicated that the COP is the sweet spot, the best place to hit the ball (Bryant, RQES 1977; Noble, ISB Proc 1983) • The sweet spot has since been defined in terms of two criteria: – The most comfortable location • The COP has a direct effect on pain/annoyance at impact (Noble, JAB 1994; Noble) • Fundamental vibrational node location also has a profound effect on impact pain/annoyance (Noble, JAB 1994) – The location for maximum post-impact ball velocity • Determined by characteristics other than COP (Brody, Am J Phys 1986) – e.g., bat/ball mass and bat vel/ball vel ratios • Vibrational node locations
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Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies indicated that the COP is the sweet spot, the best place.
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Kansas State University Biomechanics Lab
Center of Percussion & the sweet spot• Earlier studies indicated that the COP is the sweet spot, the best
place to hit the ball (Bryant, RQES 1977; Noble, ISB Proc 1983)• The sweet spot has since been defined in terms of two criteria:
– The most comfortable location • The COP has a direct effect on pain/annoyance at impact (Noble, JAB 1994; Noble)• Fundamental vibrational node location also has a profound effect on impact
pain/annoyance (Noble, JAB 1994)
– The location for maximum post-impact ball velocity• Determined by characteristics other than COP (Brody, Am J Phys 1986)
– e.g., bat/ball mass and bat vel/ball vel ratios
• Vibrational node locations
Kansas State University Biomechanics Lab
Impact vibrations and annoyance• Node of fund mode approx 17 cm (6.7 in)
from each end and 170 Hz (Cross, Am J Phys 1998)
• First harmonic is approx 530 Hz with nodes at approx 13 cm from BE, 5 cm from COM toward hands, and 7 cm from KE.
• Impacts on the node will not excite that mode.
• Mode excitation increases linearly with impact-node distance
• Thus we have a “sweet vibrations” zone approx 13-17 cm (5-6.7 in) from BE.
Kansas State University Biomechanics Lab
Vibrations, COP & Impact Annoyance• Node-COP distance is determinant of bat
preference (Noble & Dzewaltowski, Tech Report to Easton Aluminum1994)
• Impact annoyance is least at a point between node of fundamental & COP (Noble & Walker Proc ISBS, 1994)
Kansas State University Biomechanics Lab
Vibrations and Post-impact Ball Velocity
• Estimates of exit speed with 90 mph ball colliding with wood bat with COM speed of 54 mph and rotational speed about COM of 51 sec-1. Red curve is for rigid bat, blue curve is for flexible bat.
• More recently, empirical data supports these estimates
Kansas State University Biomechanics Lab
Bat Vibrations During Swing
• Manufacturer’s are claiming “diving board effect”
• This implies that bat bends back during the swing and “releases the stored elastic energy at impact, as depicted here
• Is this implication valid?
Kansas State University Biomechanics Lab
Bat Flexibility Field Test• Effects of bat handle flexibility on performance and preferences• First, a controlled blind field test involving 6 different bat flexibilities
with 32 elite softball players was funded by a bat manufacturer• Results indicated that these hyper-flexible bats resulted in greater
post-impact velocity and were preferred by elite slow-pitch hitters over stiffer bats • An examination of bat
bending characteristics during the swing followed this study