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Dynamics of Spear Throwing

TitleDynamics of Spear Throwing
Publication TypeJournal Article
Year of Publication2003
AuthorsBAUGH, R. A.
JournalAmerican Journal of Physics
Volume71
Issue4
Pages345-350
PublisherAmer Assoc Physics Teachers Amer Inst Physics
Publication LanguageEnglish
ISSN Number0002-9505
Abstract

J. Whittaker: Atlatl is a lever, operating principle is “Wrist torque applied to the length of the atlatl allows wrist rotation to increase the velocity of the dart.” Simple computer model to predict velocity of dart, affected by mass of dart and length and mass of atlatl. Horizontal force and wrist torque versus hand position derived from video record of throws; two other variables are hand mass and hand radius of gyration. Some horizontal force applied by hand, but most force from wrist rotation of the lever arm formed by atlatl. Spear, ball and atlatl throws are all the same except for the length of this lever. Can model a flexible atlatl by inserting a massless spring in model between hook and dart.
Model results: Atlatl length for max velocity is shorter than most actual use, but this may be because model assumes that human effort is not affected by mass of atlatl, or difference in velocity from atlatl length may be too small to be perceptible. Atlatl weights reduce velocity slightly, more as they are larger and further from hand. [His graph suggests up to 30% decrease in velocity with 120 gm wt at 80% of distance from hand.] Flexible atlatl should increase velocity. [But seems to have less effect than weights, maybe 12% increase. Also, his model does not take account of the dart flex, and he uses a range of spring models “representing actual practice” – but nowhere is there evidence that he actually measured atlatl flex.]
[I have a hard time evaluating the mathematical model, but the results make sense. We need more of this kind of work.]