Quantifying the Aerodynamic Forces Acting on Objects During a Fall

This article analyzes the aerodynamic forces which act on a vehicle and a human in the context of a fall calculation in order to determine the effect of aerodynamic forces on launch velocity calculations. For large bodies moving at ordinary speeds, such as a car moving through the air, the flow of air past the body creates an aerodynamic drag force which results from a combination of skin frictions and pressure drag. Including air resistance introduces variable acceleration in the direction directly opposite to a projectile's velocity. Air resistance works in conjunction with the vertical acceleration due to gravity and it changes the otherwise uniform horizontal component of motion to a decelerated motion. This change in acceleration results in a reduced maximum height and also a decreased distance traveled for an object. In a scenario involving a car that traveled through the air after being launched at a 30° angle at a speed of 45 mph, exclusion of air resistance resulted in a .9% increase in the vehicle's distance traveled and a .3% increase in the vehicle's calculated initial speed. For a scenario involving a human, the exclusion of air resistance resulted in a 4.5% increase in the human's distance traveled and a 2.2% increase in the individual's calculated initial speed. Although these particular differences in initial speed are of no significance in the context of an accident reconstruction, they do illustrate that the effect of air resistance can be quantified.