TY - JOUR A1 - Schäfle, Claudia A1 - Kautz, Christian T1 - Student reasoning in hydrodynamics: Bernoulli’s principle versus the continuity equation JF - Physical Review Physics Education Research N2 - We report on an investigation of student thinking about steady-state pipe flow of an incompressible fluid. About 250 undergraduate engineering students were given a test consisting of two hydrodynamics questions, combining multiple-choice format with subsequent open-ended explanations. There is substantial evidence that students have difficulty applying and prioritizing the two basic principles of mass conservation (expressed in the continuity equation) and energy conservation (i.e., Bernoulli’s equation). When faced with questions that involve gravity, dissipative effects (“friction”), or a visible pressure drop, a considerable number of students did not invoke the continuity equation in situations where applying it is a necessary step for arriving at the correct answer. Instead, even after lecture instruction on this topic, many of the first-year students based their answers on ill-supported assumptions about local pressures. Some of them used formal arguments from a simplified Bernoulli equation (“lower pressure means higher velocity”), while others based their answer on intuitive arguments (“higher pressure leads to higher velocity”). We also found reasoning based on analogies to single-particle motion (“flow velocity decreases when flowing upwards or friction is present”). Contrary to other researchers, we did not see any evidence for the hypothesis that students think of water as a compressible fluid. Instead, students’ answers often indicate a lack of understanding of the conservation of mass or its implications for incompressible fluids or of the role that this principle plays in the context of fluid flow. In addition, our data indicate that some students have more general difficulties in describing and reasoning about technical situations, such as applying equations containing multiple variables, distinguishing spatial differences in a quantity from its changes with respect to time, or realizing the meaning of idealizations. We also present some evidence that different levels of activation of students during instruction influence the prevalence of these difficulties and discuss some implications for instruction. KW - Physics Education research KW - Concepts& Principles KW - Instructional strategies KW - Instructional materials development KW - Strömungsmechanik Y1 - 2021 UR - https://doi.org/10.1103/PhysRevPhysEducRes.17.010147 VL - 17 IS - 1 SP - 010147 PB - American Physical Society ER - TY - CHAP A1 - Schäfle, Claudia A1 - Kautz, Christian ED - Lock, Arjan T1 - Students reasoning in fluid dynamics: bernoulli's principle vs. the continuity equation T2 - Proceedings of the 10th international conference on Physics Teaching in Engineering Education N2 - In this work we investigate students’ thinking about and difficulties with incompressible, steady pipe flow. There is substantial evidence that students have difficulty applying and prioritizing the two basic principles of mass conservation (i.e., the continuity equation) and energy conservation (i.e., Bernoulli’s equation). When distracted by questions which involve gravity students based their answers on ill-supported assumptions about local pressures. The predominant arguments use a simplified Bernoulli equation, descriptive arguments or analogies to single-particle motion. Based on these results, an instructional intervention is developed that seems to address the observed difficulties. KW - conceptual understanding KW - students' thinking KW - hydrodynamic Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:861-opus4-13104 SN - 978-90-9031874-5 SP - 1 EP - 8 ER -