Why could not a vertical line appear? Imagining to stop time

This research study concerns 9 year-old children who experienced, through the use of a technological device, position-time graphs that represent a motion happening in a vertical plane. Attention is drawn to moments of a classroom discussion, in which children are thinking of the graphs related to vertical and horizontal trajectories. In these moments, it comes to the fore the big issue of having a vertical line as one of the graphs. We want to analyse the expectation of stopping time that arises from this issue, and grows through a recollection of the past experience with graphs given by horizontal lines. To this aim, we focus on children’s words and gestures.