The weight of a book was measured using a scale. The scale showed 15N. Next, the book and the scale were placed in an elevator that does not show the floor number. When the elevator started moving, the reading of the scale has changed, but later was reading 15N again. Using the fact that the scale shows the same value in the elevator, can you tell if the elevator is moving upward or downward? What kind of information would you need to make that assessment? Explain