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The Physics of Javelin Throwing

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The Physics of Javelin Throwing

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  1. The Physics of Javelin Throwing

  2. How to Make the Javelin Fly Far 101 • Maximize release velocity • Maximize the aerodynamic efficiencies of the javelin • Maximize the height of release without compromising the first two items

  3. Qualities of the Javelin and How They Affect Flight The Evolution of Javelin Design MattiJarvin - 1932

  4. And Then Came the Scientific Application of Bernoulli’s Principle • Bernoulli's Principle states increased air velocity produces decreased pressure on the top of an airfoil (top) • Lift is produced by an airfoil through a combination of this decreased pressure above the airfoil and increased pressure beneath it (bottom) Credits - AVStop Magazine Online, Helicopter Handbook

  5. 1986 Rule Change 2011-2012 NCAA Rule Book

  6. Maximizing Aerodynamic Gaines Release velocity and aerodynamic efficiency are not correlated. Therefore, additional distance can be gained independent of release speed by maximizing aerodynamic efficiency. Aerodynamic gains are achieved by increasing lift and decreasing drag simultaneously

  7. Optimizing Release Angles The javelin’s vertical orientation angle describes the angle of the javelin in relation to the ground. The angle of attack is the angle between the release speed the vertical orientation angle of the javelin

  8. Optimizing Release Angles The javelin’s horizontal orientation angle describes the direction of the javelin to the left or right. The angle of sideslip is the angle between the release speed and javelin’s horizontal orientation.

  9. Creating Lift By utilizing a negative horizontal javelin angle and adding a slight negative sideslip angle in combination with a clockwise rotation about the javelin shaft, additional lift can be created. The rotation of the javelin causes air hitting the side of the javelin to increase the air flow over the top of the javelin, decreasing air pressure, and creating lift as described in Bernoulli's Principle.

  10. Decreasing Drag A small angle of attack reduces the surface area exposed to the air. A throw with a 0 degree angle of attack creates 10 times less drag than a javelin thrown with a 10 degree angle of attack. If all other variables remain consistent, this translates to a 7 meter difference in the throw’s distance.

  11. Decreasing Drag Similarly, increasing sideslip angles also increases drag.

  12. Decreasing Drag Rotation about the long axis of a javelin can also reduce drag. Just as the spinning wheels of a bicycle keep it from tipping side to side, the spinning of the javelin around the long axis helps it to resist forward rotation. The spinning of the javelin also stabilizes the vibration in the shaft similarly to how the rifling of a gun stabilizes the bullet.

  13. Angular Velocities and Aerodynamics Angular velocity about the center of mass in the vertical plane (forward rotation) should be no greater than 9 degrees per second. Rotation faster than this, cancels out gains due to lift. A throw rotating at 18 degrees per second will result in a throw roughly 25m less than a throw rotating under 9 degrees per second.

  14. Angular Velocities and Aerodynamics Angle of attack also affects angular velocity. A positive angle of attack creates drag on the underside of the tail and will cause the javelin to pitch forward. A negative angle of attack creates drag on the top side of the nose and will not cause the same pitching reaction.

  15. Angular Velocities and Aerodynamics Trunk Tilt Angle The trunk tilt angle represents the lean of the torso relative to true vertical. It describes the orientation of the trunk, the line of the hips and the shoulders. An excessive trunk tilt angle will result in an increase in angular velocity

  16. Angular Velocities and Aerodynamics Drills that address excessive angular velocity in the vertical plane due to trunk tilt by setting up an effective block: • Sprint drills to promote good running posture • Transition Drill to set up good posture in the cross overs • Special Strength Drills for the C Position (Square throws, Three Step Tire Drills, Static Holds) • Staggered Square Drills to promote proper hip position in the block

  17. Angular Velocities and Aerodynamics Similarly, angular velocities in the horizontal plane also effect aerodynamic efficiencies. The greater the horizontal rotation, the faster the angle of sideslip will increase. Christian Nicolay

  18. Angular Velocities and Aerodynamics Drills to address excessive angular velocities in the horizontal plane do to shoulder Rotation: • Pullie Drill • Poll Drill • Basketball Throws • Reverse Pulls

  19. Maximizing Release Velocity Release velocity is directly correlated to a throw’s distance. There is both a horizontal and vertical component to release velocity. Because humans are far more efficient at creating horizontal speed, vertical speed should only be increased so long as the horizontal component isn’t diminished.

  20. Technical Elements Affecting Release Velocity Temporal Rhythm • Time of throwing procedure (time from contact of the last right foot to release) • Time of the single support phase (time spent on the last right foot until the left foot hits) • Time of the delivery phase (time from left foot contact to release)

  21. Technical Elements Affecting Release Velocity Maintenance of Runway Speed Through the Throwing Procedure Jan Zelezny

  22. Technical Elements Affecting Release Velocity Drills that Address Inefficient Maintenance of Runway Speed: • Running Mechanics to address posture in the carry and transition phases of the throw • Crossover drills addressing posture and stride length, and footfall frequency • Right foot action (Soft Step): One step off a low box, 3 step off a low box, down hill throws

  23. Technical Elements Affecting Release Velocity Left Lower Extremity Angles • Left knee flexion angle - left leg should be straight at during the delivery phase • Left leg angle – the angle should increase in the delivery phase

  24. Technical Elements Affecting Release Velocity Hip Shoulder Separation Hip shoulder separation represents trunk twist. Trunk twist is used to convert linear motion to rotational. It can also be very effective in increasing the speed of each body segment in order away from the trunk out to the javelin in a whipping motion.

  25. Technical Elements Affecting Release Velocity Efficient Summation of Joint Speeds: the Whipping Action

  26. Technical Elements Affecting Release Velocity Drills Addressing Efficient Summation of Joint Speeds: • Hip activation drill series (low, mid and high positions) • Leverage drills (double arm wall drill, single arm wall drill, alternate wall drill, one or two hand square throws with medicine ball, turbo javelin, or javelin)

  27. Additional Elements Affecting Distance • Height of Release - as high as possible without reducing speed • Angle of Release – between 29 and 35 degrees to maximize speed of release and lift. Tom Petronoff

  28. Special Thanks To: Steve Leigh, M.S. And Bing Yu, Ph.D. Center for Human Movement Science Division of Physical Therapy The University of North Carolina at Chapel Hill Under the USATF Scientific Services Project For providing the biomechanical analysis of the javelin throw cited in this presentation.