Figure 2.

(a) Attempt to fit a sample data set with U(t) as a solution to mdU/dt = −F_D when three different drag forces are considered. U(t) = U₀ exp {−ct} when F_D ∝ U, U(t) = 1/(1/U₀ + ct) when F_D ∝ U² and $U(t)=\mathrm{1/}{(\mathrm{1/}\sqrt{U_0}+ct)}^2$ when F_D ∝ U^3/2, where c is the fitting parameter and U₀ the measured initial speed. The shaded area represents the mean speed over at least 39 runs to within two standard deviations. The slider has radius R = 4.00 ± 0.05 mm and mass m = 61 ± 2 mg, and the fluid kinematic viscosity is ν = 0.0100 ± 0.0002 cm²/s.