At a drop height of 1 cm above the water surface, the ball speed decreased from about ${v}_{1}=0.7$ m s−1 to about ${v}_{2}=0.42$ m s−1 over the 10 cm fall distance shown in figure 2. A typical result is shown in figure 3, where the vertical height of the bottom of the ball above the bottom of the tank, y, is shown as a function of time. All y(t) data for all drop heights could be fitted accurately by a quadratic with a correlation coefficient greater than 0.9999. In figure 2(a), $y=0.146-0.693t+0.746{t}^{2}$, indicating that $v=-0.693+1.492t$ and ${
m{d}}{v}/{
m{d}}{t}=1.492$ m s−2.