The underlying structure of web pages can allow them to contain images that are moved by software algorithms. With little effort, simulations can be animated by software that is on open view to the student and that will be modified 'there and then' as part of the learning exercise. The JavaScript environment allows instant execution of code with visualisations unsurpassed by many massive and expensive packages. Examples are given of dynamic demonstrations and the simple means of achieving them. With a little more effort, graphical clients can be written and embedded into web pages which r allow students to try tutorial exercises, interacting with the exercise in a diagrammatic form. Examples are given of applet and XML techniques that can make these graphical components interact with the page they are embedded in and also with the server.