Abstract
The paper is in two parts. In the first part the reflection and transmission of an incident pulse when it arrives at an interface with a semi-infinite medium is described and the ideas of nonlinear impedance, reflection coefficient and transmission coefficient are introduced. In the second part of the paper a more detailed account is given of what happens when a pulse is partially reflected and partially transmitted at an interface. This is achieved by noting that the responses of many elastic materials can be correlated, both qualitatively and quantitatively, by a family of stress vs. strain laws for which the governing nonlinear equations for this problem can be solved exactly.