A test instrument, made up of 25 items, derived from existing standardized tests from literature, was used to probe for the students' knowledge and understanding of basic mechanics concepts, as well as the confidence in the correctness of their answers. The test was administered to 982 first entering physics students; enrolled at three South African universities, at the beginning of the year before any formal instruction could take place. Data collected for this study included students' responses from multiple-choice questions and open-ended explanations to their chosen answers. The analysis of the multiple-choice responses and the written explanations revealed the existence of alternative conceptions among students and that the students' accuracy of judgment about their knowledge and understanding of basic mechanics concepts is different among the different cohorts. Physics education research, has over a number of years, revealed that students have alternative conceptions about physical processes. These alternative conceptions are accumulated from the students' past personal experiences, interactions with people around them and the environment they live in. It was found from the study that the strength of the known alternative conceptions differs among the different cohorts. There are those alternative conceptions that are easier to correct with sound teaching. These alternative conceptions exist mostly in worst performing cohorts and less so in the best performing cohorts. There are those alternative conceptions that persisted despite better teaching. These alternative conceptions are found in all the cohorts. The certainty of response analysis revealed the differences in the relationship between performance and confidence among the students from the three universities. It was also found that students make incorrect judgment about their knowledge and understanding of basic mechanics concepts. The overall trend emerging from the study was that students seem to be overconfident about their knowledge and understanding of basic mechanics concepts, but that students with a good command of mechanics concepts made the best judgment about the correctness of their answers. The item-by-item analysis of students' responses revealed that in most cases the best performing students make quality judgment about their performance, while poor perfOlming student always make inaccurate judgments about their performance. Analysis of the students' written explanations and item difficulty revealed that the Hasan et al. (1999) study is lacking in the differentiation between lack of analytical skills and the presence of alternative conceptions. Lack of analytical skills cannot be classified as evidence of the presence of alternative conceptions. The student may be having knowledge of the necessary concepts, but lack higher order analytical skills to be able to interpret situation presented. / Dissertation (MSc)--University of Pretoria, 2009. / Chemistry / unrestricted

Master’s theses “Application Physics Practical Tasks and Reasoning Schemes in Teaching Mechanic Concepts“ consists of an introduction, 3 sections, conclusions, references to literature and 3 annexes. 8 tables and 18 pictures are presented in the work. The work comprises 72 pages (83 with annexes). Application physics practical task and reasoning schemes, teaching mechanic concept is examined in the theses. The problem of pedagogical and psychological concepts’ formation is examined in section I. In section II all the methodological material (the reasoning of the tasks system, structure and content is presented). The results of the pedagogical experiment are presented in section III. The pedagogical experiment showed, that practical tasks and their conceptional schemes help pupils to improve knowledge in physics as well as an effective way to raise the motivation.

This thesis aims to reveal the correlation between stress corrosion cracking propagation behavior and Schmid and Taylor factor mismatch using EBSD analysis. <div><br></div><div>Chloride induced stress corrosion cracking (CISCC) is one of the most vulnerable weaknesses for the widely used austenitic stainless steel in many industries. The complex nature of CISCC involves mechanical, electrochemical, and microstructural perspectives. The objective of this thesis is to assess CISCC phenomenon in austenitic stainless steel from the mechanical and crystallographic perspective, specifically on the effect of local strain and stress and anisotropic plastic deformation. Austenitic stainless steel 304L test coupons are bent in four-point bending fixtures to obtain tensile stress for CISCC, followed by corrosion experiment in boiling magnesium chloride solution. Stress state of the sample is evaluated by finite element analysis (FEA) and X-ray Diffraction Crystallography (XRD) prior corrosion test. Cross section of the cracked region are analyzed with Electron Backscatter Diffraction (EBSD) to analyze the relationship between CISCC behaviors and crystallographic features in the sample. Schmid factor and Taylor factor are used to quantitatively evaluate CISCC initiation and propagation behavior. It is learned that in polycrystalline FCC stainless steel, mismatch of Schmid factor and Taylor factor values in adjacent grains along crack path governs CISCC propagation susceptibility and path selection. Crack propagation factor competition model is proposed based on observations from EBSD maps, incorporating Schmid factor and Taylor factor mismatch, electrochemical condition of crack tip, and anisotropic properties. <br></div>