AFTE Store - Lawn Mower Ballistics

Rotating parts of machines carry the risk of causing accidents. In this paper, the case of a piece of stucco being “thrown” by the rotating blade of a rotary lawn mower will be discussed. To reconstruct its ballistic trajectory, among other data, the knowledge of the departure velocity is required. While this is not a major hindrance for bullets fired from a gun, as the muzzle velocity can easily be determined, measurement is not a realistic option for objects being propelled accidentally by a rotating machine. The major challenge of this paper is to determine from pure physical principles a realistic estimate for the departure velocity of an object accelerated by a rotor. Different physical models of the acceleration process are discussed, and the resulting exterior ballistic trajectories will be shown.