In this paper we investigate the downward movement of a ball through the air followed by a dive in water. We consider the sphere under action of gravitational force, hydrodynamic drag and buoyancy force, both in air and water. As the buoyancy in water becomes larger than the gravitational force, the ball reaches a maximum depth of dive before returning to the surface. Considering the expression of quadratic drag with constant coefficient in the two fluids, we obtained an analytical expression relating the height of fall with the maximum depth of the dive. We compare this expression with numerical results which considers the drag coefficient dependent on speed and variable buoyancy while the ball passes through the air-water interface. Comparisons between the analytical and numerical results show that the "drag crisis" plays an important role at the first instants after the dive, with a significant influence on the maximum depth reached.
drag coefficient; drag crisis; free fall; plunge dive
