Many prominent lines of research on students' reasoning and conceptual change within learning sciences and physics education research have not attended to the role of learners' affect or emotions in the dynamics of their conceptual reasoning. This is despite evidence that emotions are deeply integrated with cognition and documented associations between emotions and academic performance. I present the case for research aimed at integrating emotions with models of learners' cognition. I present a case-study to argue that, in physics learning environments, learners' emotions can be intertwined with the unfolding conceptual and epistemological reasoning at fine time-scales. This case-study draws on video-taped interactions of a small group of students working on a physics tutorial. The analysis of the conceptual and epistemological substance of students' talk and the associated emotions draws on a combination of methodologies from knowledge analysis, interaction analysis, and conversation analysis traditions. I end with implications for research and instruction.