Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies...
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![Page 1: Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies indicated that the COP is the sweet spot, the best place.](https://reader030.fdocuments.in/reader030/viewer/2022032704/56649d545503460f94a30cb2/html5/thumbnails/1.jpg)
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
![Page 2: Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies indicated that the COP is the sweet spot, the best place.](https://reader030.fdocuments.in/reader030/viewer/2022032704/56649d545503460f94a30cb2/html5/thumbnails/2.jpg)
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.
![Page 3: Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies indicated that the COP is the sweet spot, the best place.](https://reader030.fdocuments.in/reader030/viewer/2022032704/56649d545503460f94a30cb2/html5/thumbnails/3.jpg)
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)
![Page 4: Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies indicated that the COP is the sweet spot, the best place.](https://reader030.fdocuments.in/reader030/viewer/2022032704/56649d545503460f94a30cb2/html5/thumbnails/4.jpg)
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
![Page 5: Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies indicated that the COP is the sweet spot, the best place.](https://reader030.fdocuments.in/reader030/viewer/2022032704/56649d545503460f94a30cb2/html5/thumbnails/5.jpg)
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?
![Page 6: Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies indicated that the COP is the sweet spot, the best place.](https://reader030.fdocuments.in/reader030/viewer/2022032704/56649d545503460f94a30cb2/html5/thumbnails/6.jpg)
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
![Page 7: Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies indicated that the COP is the sweet spot, the best place.](https://reader030.fdocuments.in/reader030/viewer/2022032704/56649d545503460f94a30cb2/html5/thumbnails/7.jpg)
Kansas State University Biomechanics Lab
Bat Vibrations During Swing & Impact
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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Time (s)
Str
ain
(v
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Horiz DirVert DirMagnitudeHoriz DirVert DirMagnitude
Begin Swing 233ms PC
Peak 41 ms PC
Horiz Pk 38 ms PC
Bat bending during swing and impact
![Page 8: Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies indicated that the COP is the sweet spot, the best place.](https://reader030.fdocuments.in/reader030/viewer/2022032704/56649d545503460f94a30cb2/html5/thumbnails/8.jpg)
Kansas State University Biomechanics Lab
![Page 9: Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies indicated that the COP is the sweet spot, the best place.](https://reader030.fdocuments.in/reader030/viewer/2022032704/56649d545503460f94a30cb2/html5/thumbnails/9.jpg)
Kansas State University Biomechanics Lab
Begin swing 183 ms PC
Peak bending and peak torque ~ 50 ms PC
Impact – bat still bentback approx 20% of max
![Page 10: Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies indicated that the COP is the sweet spot, the best place.](https://reader030.fdocuments.in/reader030/viewer/2022032704/56649d545503460f94a30cb2/html5/thumbnails/10.jpg)
Kansas State University Biomechanics Lab
Wood vs Aluminum Bats
• Estimates of post-impact ball velocity of wood and aluminum bat
• Aluminum bats are better because– COR is higher– Length and weight are independent– Aluminum bats have lower
Moment of inertia– Stiffness can be a design feature– Node-COP location can be a
design feature
![Page 11: Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies indicated that the COP is the sweet spot, the best place.](https://reader030.fdocuments.in/reader030/viewer/2022032704/56649d545503460f94a30cb2/html5/thumbnails/11.jpg)
Kansas State University Biomechanics Lab
Conclusions: Bat Vibrations During Swing and Impact
• During the swing, the bat bends back and stores elastic energy that is released during impact
• Thus, a more flexible bat would appear to be more effective if the ball impacts at the sweet spot
• During impact, the bat behaves as a free-free body• A stiffer bat would appear to be more effective if the ball
does not impact at the sweet spot.• Perhaps a stiff bat is better for baseball and fast-pitch
softball and a flexible bat is better for slow-pitch softball
![Page 12: Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies indicated that the COP is the sweet spot, the best place.](https://reader030.fdocuments.in/reader030/viewer/2022032704/56649d545503460f94a30cb2/html5/thumbnails/12.jpg)
Kansas State University Biomechanics Lab
So, Where and What is Sweet Spot?• It is the best place on the bat to hit the ball,
considering– Annoyance/comfort– Post-impact ball velocity
• This location is:– Location of minimal vibrations (approx 6.5 in from
barrel end)– Location of COP with axis approx 6 in from knob end
(approx 6 in from barrel end)– Preferably these two areas are close together
![Page 13: Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies indicated that the COP is the sweet spot, the best place.](https://reader030.fdocuments.in/reader030/viewer/2022032704/56649d545503460f94a30cb2/html5/thumbnails/13.jpg)
Kansas State University Biomechanics Lab
Criteria for evaluating baseball & softball bats
• Overall feel, grip, how does it fit your hand(s)• Post impact ball response
– Control– Power
• Durability– Resistance to denting, cracking, etc. under normal playing
conditions
• Forgiveness – size of sweet spot• Construction quality
– End cap, knob, welds, finish
• Would you buy the same bat again?
![Page 14: Kansas State University Biomechanics Lab Center of Percussion & the sweet spot Earlier studies indicated that the COP is the sweet spot, the best place.](https://reader030.fdocuments.in/reader030/viewer/2022032704/56649d545503460f94a30cb2/html5/thumbnails/14.jpg)
Kansas State University Biomechanics Lab
Softball bat websites to check out
• Technical notes on bats: Baseball & Softball Knowledge Base
• Product reviews: http://www.batreviews.com/
http://www.bandnsoftball.com/ (costs $50 per year)
• Where to buy them: BallGloves.com
• Physics of baseball bats - Alan Nathan
• UMass Bat Research Center
• Physics and acoustics of bats - Dan Russell