Visualisation is a powerful tool in research; visual, dynamic and interactive representations help learners using simulations and microworlds to gain qualitative understanding of concepts. Recorded video can bring reality to computer assisted learning. The author argues that the two approaches, while complementary, are not entirely compatible; that is, the use of video images in simulations often implies a trade-off against qualitative modelling power. Appropriate roles for video are discussed in the light of this contention.