Experimental Investigation of the Hydrodynamic Interactions between a Sphere and a Large Spherical Obstacle J. Phys. The displacement of the particle is followed by laser interferometry with a 100 nm resolution. The large obstacle is either convex, plane or concave. The experimental results for the drag coefficient on the particle are compared to the theoretical results written as three terms expansions for small gaps, viz.
Excellent agreement is found between the experimental and the theoretical results for all cases.