Using computers to provide dynamic modelling of physical situations is a valuable teaching tool. This is the first of two articles which look in detail at the use of two tools: this article considers the use of VnR whilst the second considers Modellus. This article provides useful approaches using VnR to teach physics. It also considers the modelling tools themselves, their advantages and the need for teachers to be both developing these tools and searching them out. It concludes with a discussion of the place of mathematics as a way of representing patterns rather than manipulating numbers.