We study by means of numerical simulations the size dependences for sound velocity of model nanostructures. We use molecular dynamics to obtain the zero temperature size dependences of the propagation velocity of mechanical perturbation for rod‐shaped nanostructures with free surfaces. The particles interact with the Stillinger–Weber potential for silicon. We consider the longitudinal sound propagation in the (001) direction only. The bulk limit is reached very quickly and the longitudinal velocity is already independent of the cross section for a nanofiber larger than 40×40 A˚. We also study velocity for structures without free surfaces and the effect of changing the magnitude of the triplet interaction potentials. ©1996 American Institute of Physics.