The paper is devoted to the estimation of hydrodynamic forces induced by different flows around an isolated solid sphere. The goal of the study is to relate the stresses exerted by the flow around the particle to the upstream flow characteristics, in particular in terms of velocity gradient in the case of pure shear flow. Three-dimensional numerical simulations have been performed. Fluent(R) code has been used. The computational flow dynamics (CFD) code has been first validated in classical cases of (i) uniforrn flow around a fixed spherical particle at low and finite Reynolds numbers (1 to 300) and (ii) linear shear superimposed to a uniform flow past a fixed spherical particle at finite Reynolds numbers (10 to 100). After the validation step of the study, the CFD code has been applied to pure linear shear flow around a fixed spherical particle. The effect of free rotation of the sphere has been analysed. The magnitude of the forces exerted on each hemisphere of a spherical particle is derived in this paper compared to forces inducing floc breakup.