In this paper we present two simulations designed with GeoGebra that illustrate dynamically a key concept in Vector Calculus: line integrals of vector fields, along with other associated mathematical properties and applications. Students are not required to know the GeoGebra environment: a user-friendly interface with buttons, functionalities and online help and exemplar problems allows immediate use of the simulations. The goal of the simulations is to enhance student insight, in the spirit of learning by experimentation, by analysing the dynamic representations provided by the simulations and by dragging objects and changing the parameters involved. The numerical results can be confirmed for special cases by standard undergraduate calculations.