2D Projectile Motion Tutorial #7

In the this tutorial, after we got most of the trajectory calculation concentrated in just two columns, we will write a custom VBA function (dual output) to replace the spreadsheet computations used. This process of  starting with very simple models, then refining the calculations and then learning how to write custom functions for those calculations will be extremely useful later for developing more complex models.

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This article has 2 Comments

  1. Thanks for the comment Mark. Your formulas and assumption are too obvious to mention. Contrary to what you are saying my model was designed for static air and it does take into account the relative speed of the projectile relative to air. To give you the proof, take your formulas and plug in zero wind speed and you shold get the same result. My goal was rather proving the numeric method and not getting into the little details (there are much better free tools out there I believe which have all the options that shooters could use). Had I done that, I would have considered the correct Cx in the first place (sub, trans and supersonic) and the wind on both coordinates, transversal Cx, Coriolis acceleration, Magnusson effect with the rotation of projectile etc etc. The correct Cx has a far larger effect than say, few meters of frontal wind. George

  2. I too have been modeling projectile motion in excel but for particulates in an air stream. The way the drag force equation, F_d = 1/2 * rho_air * C_d * A * V^2, is used in your models, it only takes into account the velocity of the projectile itself. The velocity in this equation actually refers to the relative velocity of the projectile in the medium it is traveling in. For example, if a projectile is fired horizontally at 5 m/s into a tailwind also at 5 m/s, then the V in F_d in the X direction is zero. The projectile would only experience drag forces in the Y direction as it falls. The corrected equation for drag is F_d = 1/2 * rho_air * C_d * A_projectile * (V_projectile – V_air)^2. This small change adds a lot of accuracy to your model.

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