# the physics of javelin throwing

Post on 23-Mar-2016

80 views

Category:

## Documents

Tags:

• #### drag rotation

Embed Size (px)

DESCRIPTION

The Physics of Javelin Throwing. 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. Qualities of the Javelin and How T hey A ffect F light. - PowerPoint PPT Presentation

TRANSCRIPT

The Biomechanics of Javelin Throwing

The Physics of Javelin Throwing

How to Make the Javelin Fly Far 101Maximize release velocity

Maximize the aerodynamic efficiencies of the javelin

Maximize the height of release without compromising the first two itemsQualities of the Javelin and How They Affect FlightThe Evolution of Javelin Design

Matti Jarvin - 1932

And Then Came the Scientific Application of Bernoullis PrincipleBernoulli'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

1986 Rule Change2011-2012 NCAA Rule Book

Maximizing Aerodynamic GainesRelease 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

Optimizing Release AnglesThe javelins 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

The javelins 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 javelins horizontal orientation.

Optimizing Release AnglesCreating 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. Decreasing DragA 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 throws distance.

Similarly, increasing sideslip angles also increases drag.

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.Decreasing DragAngular Velocities and AerodynamicsAngular 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.

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.

Angular Velocities and AerodynamicsAngular Velocities and AerodynamicsThe 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 velocityTrunk Tilt Angle

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 blockAngular Velocities and AerodynamicsAngular Velocities and AerodynamicsSimilarly, angular velocities in the horizontal plane also effect aerodynamic efficiencies. The greater the horizontal rotation, the faster the angle of sideslip will increase.

Christian NicolayDrills to address excessive angular velocities in the horizontal plane do to shoulder Rotation:

Pullie DrillPoll DrillBasketball ThrowsReverse PullsAngular Velocities and AerodynamicsMaximizing Release Velocity Release velocity is directly correlated to a throws 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 isnt diminished.Technical Elements Affecting Release VelocityTemporal RhythmTime 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)

Technical Elements Affecting Release VelocityMaintenance of Runway Speed Through the Throwing Procedure

Jan Zelezny

Drills that Address Inefficient Maintenance of Runway Speed:Running Mechanics to address posture in the carry and transition phases of the throwCrossover drills addressing posture and stride length, and footfall frequencyRight foot action (Soft Step): One step off a low box, 3 step off a low box, down hill throwsTechnical Elements Affecting Release VelocityTechnical Elements Affecting Release VelocityLeft Lower Extremity AnglesLeft knee flexion angle - left leg should be straight at during the delivery phase

Left leg angle the angle should increase in the delivery phase

Technical Elements Affecting Release VelocityHip 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.Technical Elements Affecting Release VelocityEfficient Summation of Joint Speeds: the Whipping Action

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)

Technical Elements Affecting Release VelocityAdditional Elements Affecting DistanceHeight of Release - as high as possible without reducing speedAngle of Release between 29 and 35 degrees to maximize speed of release and lift.

Tom Petronoff

Special Thanks To:

Steve Leigh, M.S.AndBing Yu, Ph.D.

Center for Human Movement ScienceDivision of Physical TherapyThe University of North Carolina at Chapel Hill

Under the USATF Scientific Services ProjectFor providing the biomechanical analysis of the javelin throw cited in this presentation.

Recommended