Measuring the Effects of Lift and Drag on Projectile Motion

The trajectory of a projectile through the air is affected both by gravity and by aerodynamic forces.¹ The latter forces can conveniently be ignored in many situations, even when they are comparatively large. For example, if a 145-g, 74-mm diameter baseball is pitched at 40 ms⁻¹ (89.5 mph), it experiences a drag force of about 1.5 N. The gravitational force on the ball 1.42 N. Nevertheless, the trajectory of a baseball pitched without spin is not strongly affected by the drag force. Because the ball is relatively heavy and the flight distance is relatively small (about 60 ft), the drag force reduces the ball speed by only about 10% by the time it reaches the batter. As a result, the time taken for the ball to reach the batter is only about 5% longer than in a vacuum, and the actual trajectory is also very similar.²