Polymer-coated nanoparticles have a wide variety of applications including drug delivery, adhesives, coatings, and magnetics. Although their complexity precludes atomistic simulations of large numbers of nanoparticles in solution, using large-scale molecular dynamics simulations, it is possible to study the interaction between pairs of nanoparticles in an explicit solvent and express these interactions in terms of empirical forces such as solvation, depletion, and lubrication forces. From these simulations, we can compute the forces exerted on nanoparticles treated with explicit-atom models, which can be used in coarse-grained simulations at larger length and time scales. In particular, we present results between two bare or polymer-grafted silica nanoparticles as a function of chain length, core size, and approach velocity. We show the work required to bring together two bare silica nanoparticles in water, alkylsilane-coated nanoparticles in decane, or poly(ethylene oxide)-coated nanoparticles in water, and compare them to the expected behaviors of nanoparticles in solution. We also examine the “equilibrium” forces on a pair of stationary nanoparticles, as well as the work required to retract the particles following an approach.