In a diagnosis survey about ballistics, given to a group of undergraduate students, a high percentage of wrong answers was obtained about estimates of air resistance and other phenomena affecting the movement of a projectile. These mistakes are related to a simplified model widely used in textbooks as well as in lectures. This model assumes that the variation of velocity depends only on gravity. Although this simplification is admissible at this level of teaching, it is not appropriately explained that in many practical cases this idealized model can lead to considerable systematic errors if the hypotheses and validity scope are not duly analyzed. A teaching strategy to overcome these difficulties is proposed. Trajectories of the conventional model are compared with other trajectories computed numerically, including different forces and effects (air resistance, buoyancy, Coriolis force, air density profile). The numerical trajectories are analyzed under different conditions. Also, the viability of some simplifications is discussed, considering the systematic error that they introduce.
Keywords:
ballistics; validity scope; conventional model; numerical analysis; systematic errors
