What is engineering? What do engineers do? How is engineering related to, but distinct from, science? These questions all relate to the nature of engineering (NOE), and as engineering is incorporated into K-12 education across the United States (Moore et al., 2015), the nature of engineering is becoming increasingly important for students and teachers. While many policy documents call for students to learn more about the structure of the engineering discipline (e.g., NAE, 2008; NAE & NRC, 2009; NRC, 2014), little has been done to define the NOE construct. This paper presents key dimensions of the nature of engineering via a framework synthesized from studies of the engineering discipline from philosophical, historical, and sociological perspectives, as well as perspectives from within the engineering field. The framework identifies and elaborates nine features of engineering, each of which capture an important aspect of the nature of engineering. For teachers, these features serve as points of entry for discussing nature of engineering ideas with students. For researchers, the features provide a set of constructs to guide future inquiries into teachers' and students' nature of engineering knowledge.

X-ray reflectivity and fluorescence near total reflection experiments were performed to examine the affinities of divalent ions (Ca(2+) and Ba(2+)) from aqueous solution to a charged phosphatidic acid (PA) surface. A phospholipid (1,2-dimyristoyl-sn-glycero-3-phosphate, DMPA), spread as a monolayer at the air/water interface, was used to form and control the charge density at the interface. We find that, for solutions of the pure salts (i.e., CaCl(2) and BaCl(2)), the number of bound ions per DMPA at the interface is saturated at concentrations that exceed 10(-3) M. For 1:1 Ca(2+)/Ba(2+) mixed solutions, we find that the bound Ca(2+)/Ba(2+) ratio at the interface is 4:1. If the only property determining charge accumulation near PA were the ionic charges, the concentration of mixed Ca(2+)/Ba(2+) at the interface would equal that of the bulk. Our results show a clear specific affinity of PA for Ca compared to Ba. We provide some discussion on this issue as well as some implications for biological systems. Although our results indicate an excess of counterion charge with respect to the surface charge, that is, charge inversion, the analysis of both reflectivity and fluorescence do not reveal an excess of co-ions (namely, Cl(-) or I(-)).

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To effectively incorporate engineering into their instruction, K-12 teachers need sufficient knowledge of the engineering discipline. An important component of teachers' engineering knowledge is their understanding of the nature of engineering: what engineers do, the epistemological underpinnings of engineering, and the relationships between engineering and other fields of study. In this study, we present a quantitative tool that was developed to assess teachers' knowledge of a particular nature of engineering dimension: the scope of engineering, which describes the demarcation between engineering and non-engineering. This tool was used to assess the knowledge of teachers and engineering graduate students, before and after they participated in a research project focused on improving elementary science and engineering instruction. Our results indicate that the scope of engineering knowledge of all participants, including the engineering graduate students, improved over the course of the project. Unexpectedly, we found that engineering graduate students were no more knowledgeable about the scope of engineering than the teachers in the study. We explore potential reasons for this result, propose recommendations for future use of the scope of engineering instrument, and discuss promising avenues for future instrument development.

Refraction is a foundational concept within introductory physics. Physics students need a deep understanding of refraction, including Snell’s Law, in order to progress towards more complex optics topics such as lenses and images. Unfortunately, many physics students obtain only a superficial understanding of refraction. Although many students can use Snell’s Law to perform basic calculations, the mathematical relationship is often divorced from students’ conceptual knowledge, which often harbours misconceptions. In this article, we describe a sequence of instructional activities that we have used in an introductory optics course that aims to address common issues of students’ learning of optics. Instead of leading with Snell’s Law and emphasising calculations, the instructional sequence places conceptual understanding in the foreground. Mathematical representations are introduced only after students have developed a conceptual foundation; in this way, mathematics becomes integrated with students’ conceptual understanding rather than existing apart from it. After describing the instructional sequence, we present the impacts of instruction on student thinking and also suggest potential applications of the instructional principles that guided our decision-making.