Experimental verification of fractional history effects on the viscous dynamics of small spherical particles

We investigate the low Reynolds, high-frequency particle response of non-neutrally buoyant particles suspended in a fluid. Gravity effects are suppressed by means of a very thin tether, whose effect on the horizontal movement of the particle is negligible due to the small amplitude, high-frequency nature of the forcing. The measured stationary responses of particles of different densities closely match the theoretical predictions for the full solution, including Basset history effects for both the amplitude ratio and the phase, and clearly differ from the solution where the history force is neglected.