In studying sand transport by ocean waves, A. Shields in 1936 postulated that the bottom shear stress required to move particles depends upon gravity g,

In studying sand transport by ocean waves, A. Shields in 1936 postulated that the bottom shear stress τ required to move particles depends upon gravity g, particle size d and density ρp, and water density ρ and viscosity μ. Rewrite this in terms of dimensionless groups (which led to the Shields Diagram in 1936).