@font-face { font-family: "Times New Roman"; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0cm 0cm 4pt; text-align: justify; font-size: 9pt; font-family: "Times New Roman"; }table.MsoNormalTable { font-size: 10pt; font-family: "Times New Roman"; }div.Section1 { page: Section1;Mechanics, first experienced by engineering students in introductory physics courses, encompasses an important set of foundational concepts for success in engineering. However, although it has been well known for some time that acquiring a conceptual understanding of mechanics is one of the most difficult challenges faced by students, very few successful attempts to engender conceptual learning have been described in the literature. On the contrary, research has shown that most students participating in university levelcourses had not acquired a Newtonian understanding of mechanics at the end of their respective course. Recently I have described more than 10 years of experiences of designing and using conceptual labs in engineering education that have successfully fostered insightful learning. In the framework of the larger project I have developed labs applying variation theory in the design of task structure and using sensor-computer-technology (“probe-ware”) for collecting and displaying experimental data in real-time. In previous studies, I have shown that these labs using probe-ware can be effective in learning mechanics with normalised gains in the g≈50-60% range and with effect sizes d≈1.1, but that this technology also can be implemented in ways that lead to low achievements. One necessary condition for learning is that students are able to focus on the object of learning and discern its critical features. A way to establish this, according to the theory of variation developed by Marton and co-workers, is through the experience of difference (variation), rather than through the recognition of similarity. In a lab, an experiential human–instrument–world relationship is established. The technology used places some aspects of reality in the foreground, others in the background, and makes certain aspects visible that would otherwise be invisible. In labs, this can be used to bring critical features of the object of learning into the focal awareness of students and to afford variation. In this study, I will account for how the design of task structure according to variation theory, as well as the probe-ware technology, make the laws of force and motion visible and learnable and, especially, in the lab studied make Newton’s third law visible and learnable. I will also, as a comparison, include data from a mechanics lab that use the same probe-ware technology and deal with the same topics in mechanics, but uses a differently designed task structure. I will argue that the lower achievements on the FMCE-test in this latter case can be attributed to these differences in task structure in the lab instructions. According to my analysis, the necessary pattern of variation is not included in the design. I will also present a microanalysis of 15 hours collected from engineering students’ activities in a lab about impulse and collisions based on video recordings of student’s activities in a lab about impulse and collisions. The important object of learning in this lab is the development of an understanding of Newton’s third law. The approach analysing students interaction using video data is inspired by ethnomethodology  and conversation analysis, i.e. I will focus on students practical, contingent and embodied inquiry in the setting of the lab. I argue that my result corroborates variation theory and show this theory can be used as a ‘tool’ for designing labs as well as for analysing labs and lab instructions.  Thus my results have implications outside the domain of this study and have implications for understanding critical features for student learning in labs.