In the First Day, Galileo addressed topics that were discussed in Aristotle's Physics and also the Aristotelian school Mechanics. It also provides an introduction to the discussion of both of the new sciences. The likeness between the topics discussed, specific questions that are hypothesized, and the style and sources throughout give Galileo the backbone to his First Day. The First Day introduces the speakers in the dialogue: Salviati, Sagredo, and Simplicio, the same as in the Dialogue. These three people are all Galileo just at different stages of his life, Simplicio the youngest and Salviati, Galileo's closest counterpart. It also provides an introduction to the discussion of both of the new sciences. The second day addresses the question of the strength of materials.