Haptic interactions with stiff virtual surfaces feel more realistic when a short-duration transient is added to the spring force at contact. But how should this event-based transient be shaped? To answer this question, we present a targeted user study on virtual surface realism that demonstrates the importance of scaling transients correctly and hints at the complexity of this dynamic relationship. We then present a detailed examination of the dynamics of tapping on a rigid surface with a hand-held probe; theoretical modeling is combined with empirical data to determine the influence of impact velocity, impact acceleration, and user grip force on the resulting transient surface force. The derived mathematical relationships provide a formula for generating open-loop, event-based force transients upon impact with a virtual surface. By incorporating an understanding of the dynamics of real interactions into the re-creation of virtual contact, these findings promise to improve the performance and realism of a wide range of haptic simulations.