The mechanics of horses pulling loads

Summary The mechanics of a horse pulling a rolling load is examined. With a draft angle of zero, shafts parallel to the ground, the horse must only exert a horizontal force to move the load. When a draft angleis present, the shafts are at some angle to the ground, the horse must exert the same horizontal force as well as a vertical force since the load is pulling back and down on the horse. This is related to the observation that horses can move faster pulling rather than carrying a given load at a given gait. The horse does not move at constant velocity, at the fast gaits at least, because of air resistance during the time all four feet are off the ground. The horse decelerates while airborne and must reaccelerate when the feet are on the ground. The effect of moving the driver on a cart is examined with the tentative conclusion that any “lightening” effect on the horse may be obviated by the increased rolling friction at the cart wheel. The pathogenesis of two forms of tarsal arthrosis, spavin, is examined in the light of the mechnical observations.