Biology 438 April 5 th , 2012 Parth Patel Biomechanics of a Wrist Shot - PowerPoint Presentation

Biology 438April 5th, 2012Parth Patel Biomechanics of a Wrist Shot

Basic PrinciplesThree types of shotsSlap ShotSnap ShotWrist ShotPower generation Weight transfer Stick Flexion Wrist Snap

Muscles Used for Power GenerationLegs – Weight TransferHamstringsQuadricepsGluteus maximus Gluteus medius Gluteus minimus Hips / Core - Rotation Hip abductorsRectus AbdominusObliques

Muscles Used for Power GenerationUpper BodyEnergy Harnessing and ReleaseShouldersBiceps/TricepsForearms Uses the momentum created from weight transfer and rotation, converts it into a quick, powerful wrist snap Recruits the use of fast-twitch fibers in the forearms High V max , high force, and high power

More About Stick FlexDuring any kind of shot, the stick turns into a spring storing energyWhen the spring is released, the energy accelerates the puckProper slap shot techniqueSource: http://hockeystickexpert.com/hockey-stick-flex/

Wrist Shot FlexStick flex is usually seen in more violent movementsIt takes a considerable amount of force to “load” the shaftDo the principles of stick flex for slap shots and snap shots apply to wrist shots?

Experimental QuestionHow does shaft stiffness on a hockey stick influence potential energy storage and subsequent shot velocity during a wrist shot?Approach:Analyze and compare the biomechanics of wrist shots with both a flexible composite stick, and a stiffer wooden stick

Wood Stick

Composite Stick

Kinematic Descriptions Composite Wood Lower hand acceleration Lower hand peak velocity Composite Wood Lower hand acceleration 45.40 m/s 2 45.64 m/s 2 Lower hand peak velocity Composite Wood Lower hand acceleration 45.40 m/s 2 45.64 m/s 2 Lower hand peak velocity 7.295 m/s 7.064 m/s

Kinematic Descriptions Composite Wood Stick Blade Velocity Puck Speed Composite Wood Stick Blade Velocity 19.24 m/s 17.60 m/s Puck Speed Composite Wood Stick Blade Velocity 19.24 m/s 17.60 m/s Puck Speed 28.32 m/s (63.7 mph) 25.22 m/s (56.7 mph)

Narrowing Our QuestionAssuming that wrist, arm, and body movements are identical regardless of which stick is being usedCan we explain the extra shot speed from the flex in the stick?And assuming that the wrist snap is the same with both sticksCan we explain the extra stick speed from the flex in the stick?

Force and Energy MeasurementsIn a three-point bending test:Where E is the Young’s Modulus of the material I is the second area moment of the cross section L is the length of the beam 𝛿 is the static deflection at the midpoint of the beam Source: Russell, Dan, and Linda Hunt. "Spring Constants for Hockey Sticks."

Flex RatingsAll composite sticks have a flex rating on the shaftFlex is measured by the number of pounds of force needed to bend the shaft 1 inch from its equilibrium

Converting Flex to SI UnitsComposite stick with Flex rating of 6565 lbs of force needed to bend the shaft at the midpoint by 1 inchWooden stick with approximated Flex of 100100 lbs of force needed to bend the shaft at the midpoint by 1 inch

Comparisons to LiteratureMost professionals use sticks with Flex Ratings anywhere from 80 – 160According to the cited study, shaft stiffness was classified under four categories:Medium (13 kN m-1) Stiff (16 kN m-1) Extra Stiff (17 kN m-1)Pro Stiff (19 kN m-1 ) Source: Pearsall, D. J., D. L. Montgomery, N. Rothsching , and R. A. Turcotte . "The Influence of Stick Stiffness on the Performance of Ice Hockey Slap Shots."

Potential Energy Storage U = ½ (11,383) (.07837) 2 U = ½ (17,513) (.04237) 2 U =34.96 Joules U = 15.72 Joules

What happens to this energy?Obviously, this energy is not released back into the shotFor reference, there were 35 (composite) and 16 (wood) joules stored in the sticks. The launch velocities measured correspond to 40 (composite) and 32 (wood) joules into the puck. But can it at least account for the difference in stick blade velocity at the release point?

Elastic Energy to Rotational EnergyThe motion we’re interested in is the speed of the stick blade as it rotates through the puckChoose to ignore the loss of stored energy, and instead focus on how much energy goes into rotating the stick bladeRotational kinetic energy can be calculatedKE = ½ I ω 2

Elastic Energy to Rotational EnergyConsider the upper hand as stationary, and assume that the stick rotates around that point

CalculationsVelocity = R ωComposite stick blade release velocity = 19.24 m/sRadius = 1.12 meters ω = V/R = 17.18 radians/sec (2.7 rev/sec) Wood stick blade release velocity = 17.60 m/s Radius = 1.12 meters ω = V/R = 15.71 radians/sec (2.5 rev/sec)

CalculationsI = moment of inertia = Istick + I blade+puck I = moment of inertia = 1/3 ML 2 + MR 2 I = 1/3 (.400 kg) (1.20 m)2 + (.100 kg + .102 kg) (1.20 m)2 I = 0.4829 kg m 2 Difference in Kinetic Energy KE = ½ I ω composite 2 – ½ I ω wood 2 KE = ½ I ( ω c 2 – ω w 2 ) KE = ½ (0.4829) [17.18 2 – 15.71 2]KE = 11.67 joules

CompositeWood Spring Constant, k 11,383 N/m 17,513 N/mMax Deflection, Δ x 0.07837 m 0.04237 Potential Energy Stored 34.96 J 15.72 J Potential Energy Difference 19.24 Joules Results Composite Wood Spring Constant, k 11,383 N/m 17,513 N/m Max Deflection, Δ x 0.07837 m 0.04237 Potential Energy Stored34.96 J15.72 JPotential Energy Difference 19.24 Joules Angular Speed of Stick at Time of Puck Release 17.18 radians/sec 15.71 radians/sec Rotational Kinetic Energy 71.26 J 59.59 J Kinetic Energy Difference 11.67 Joules Composite Wood Spring Constant, k 11,383 N/m 17,513 N/m Max Deflection, Δ x 0.07837 m 0.04237 Potential Energy Stored 34.96 J 15.72 J Potential Energy Difference 19.24 Joules Angular Speed of Stick at Time of Puck Release 17.18 radians/sec 15.71 radians/sec Rotational Kinetic Energy 71.26 J 59.59 J Kinetic Energy Difference 11.67 Joules Storage Efficiency 60.65%

SummaryThe composite stick is able to store more energy than the wood stickThe excess energy storage is used to increase the rotational kinetic energy of the stick at the time of puck releaseThe efficiency of this conversion from elastic potential to rotational kinetic energy is 60%Under the same movement, the composite stick is able to launch the puck 7 miles per hour faster than the wood stick

ImplicationsThis supports evidence that advises hockey players to buy the stiffest hockey stick they can flex easilyAlso explains why only a handful of NHL players still use wood sticks

ConclusionsThis finding should not be surprising, as this relationship is also common in nature.Recover the most energy from a given force using a spring with the lowest spring constant

Further InvestigationThe effect of different kickpoints on shot velocityMid flex vs. Low kickpoints

Sources"Ice Hockey Sticks | Hockey Stick Flex: Produce Better Shots With The Right Flex/Stiffness." Web log post. Hockey Stick Flex: Produce Better Shots With The Right Flex/Stiffness. Web. 28 Mar. 2012. <http://hockeystickexpert.com/hockey-stick-flex/>.Russell, Dan, and Linda Hunt. "Spring Constants for Hockey Sticks." The Physics Teacher (2009). Print.Laliberte, David. "Biomechanics of Ice Hockey Slap Shots: Which Stick Is Best?" Biomechanics of Ice Hockey Slap Shots: Which Stick Is Best? The Sports Journal, 2009. Web. 02 Apr. 2012. <http://www.thesportjournal.org/article/biomechanics-ice-hockey-slap-shots-which-stick-best>. Pearsall, D. J., D. L. Montgomery, N. Rothsching , and R. A. Turcotte. "The Influence of Stick Stiffness on the Performance of Ice Hockey Slap Shots." Sports Engineering 2.1 (1999): 3-11. Print.