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Dynamics of Spear Throwing presented to The American College of Sports Medicine by Richard Baugh, May 30, 2003, based on a paper published in the American Journal of Physics, 71, (4), April 2003. Pp 345 - 350. Introduction Spear thrower = atlatl = woomera = propulsore = propulseur
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Dynamics of Spear Throwingpresented to The American College of Sports Medicineby Richard Baugh, May 30, 2003, based on a paper published in the American Journal of Physics, 71, (4), April 2003. Pp 345 - 350
Spear thrower = atlatl = woomera = propulsore = propulseur
Efficient propulsion of a lightweight projectile
Dave Engvall threw 848 feet = 258.5 meters,
Dave’s average speed > 165 feet/sec
Spearthrower carved from
Late Magdalenian spear thrower, horse effigy carved in reindeer antler
An ibex kid, reindeer antler
Projectile velocity depends on Dimensions,
Weight distribution and Flexibility
Human effort is inconsistent so…
Simple enough to be tractable
Detailed enough to give useful results
Same moderate physical effort applied to all throws
Forward force and wrist torque are functions only of horizontal hand position.
Muscles contract with a force that is independent of contraction rate
Consequently physical effort is independent of mass and dimensions of the projectile or spear thrower
Vertical force can be absorbed into the applied torque
Hand has measurable mass and radius of gyration.
Heavy projectile: Throw from palm
Baseball: Throw from finger tips
Lighweight spear: Throw from the end of a stick
Measure position and angle versus time
Numerically differentiate twice
Do inverse dynamics using the known masses and moments of inertia
Experimental data obtained at UC Davis (Mont Hubbard)
.005 second increments
Initial position on the left, final on the right.
(Note added spring)
Negative angular acceleration is due to forward force
The longer the lever arm, the more significant the negative angular acceleration becomes
A simple computational model for the spear thrower
Opportunities for improvement:
More accurate model of muscle contraction force versus contraction rate
How is accuracy is affected by atlatl and projectile dimensions and mass distribution?
More experimental data