Forces on a saltating grain in air.

A wind tunnel experiment was performed to measure the trajectories of individual sand grains. Then, the acceleration given by the numerical differentiation was used to assess the relative importance of different external forces on a saltating sand grain in air. It is reconfirmed that the gravitational force and drag are the most important to grain motion. The lift also has certain influence. However, the present research does not support that the electrostatic force is significant.