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Fluids thread

Page history last edited by Joe Redish 2 years, 3 months ago

NEXUS/Physics > Threads



This page includes an instructional "thread" on random motion and diffusion. While the physics associated with these concepts are not covered in traditional introductory physics classes, these topics are of great importance in biology and chemistry, especially in cellular and subcellular biology and in biochemistry. For this reason, we have chosen to include a significant consideration of the physics underlying these phenomena in NEXUS/Physics. The materials provided include:


  • Readings -- text describing the random motion model and thermal fluctuations;
  • Homework problems -- tasks for out-of-class work for students to complete on their own;
  • Peer instruction questions -- clicker questions for encouraging in-class discussion;
  • Recitation activities -- guided activities for use in recitation sections with students working together in groups;
  • Quiz and exam problems -- problems that can be used for either formative or summative assessment throughout the class.
  • Laboratories -- a set of laboratories that permit students to make direct observations and measurements of random motion and diffusion, including observations within a living biological system. 





The reason that random motion models and diffusion are so important at the cellular and sub-cellular scale is the fact that thermal energy is associated with the random motion of molecules. As a result, a deeper understanding of random motion at the micro- (and nano-) level requires an understanding of the basic concepts of statistical mechanics: thermal energy, equipartition, the Boltzmann factor, and entropy. While a full treatment of these sophisticated topics is beyond the scope of an introductory physics class, some basic elements need to be included in order to build a coherent discussion of both diffusion and essential thermodynamics. Some of our readings related to basic statistical mechanical issues are here:




Homework problems:


The out-of-class activities are intended to be done by students out of class working together. These are intended to be challenging problems that require deep thought about the fundamental concepts and a bringing together of concepts learned in biology and chemistry with the physics that is being studied. Problems include a wide range of activities, from multiple choice to essay questions and estimation problems. Solutions are available for those items followed by an asterisk (*). The solutions may be reached by certified instructors by clicking on the asterisk. To get certified for these solutions, contact Joe Redish.




Peer Instruction Questions:


These are presented as slides in PowerPoint booklets to allow faculty to easily include them in their lectures. The clicker slides in this booklet are meant to be used as stimuli to encourage class discussion. They are intended for use in a class that attempts to help students develop a coherent and sophisticated understanding of scientific thinking. They are NOT intended as items to test whether students are “right or wrong” or “know” the correct answer by one-step recall if enough cues are given. (The direct links yield the PowerPoint versions some of which contain notes giving suggestions for use. The "pdf" links are PDF files of the slides without the notes.)


The topics covered in this packet include random motion and kinetic theory.




Recitation activities


These tasks are intended for small group problem-solving and discussion, and are intended to help students build strong conceptual fundamental understanding of the physics and to make the connection with what they know from biology and chemistry. They are not intended to be collected and graded. They are most effective when students work in groups of 3 to 5 and are given encouragement to think about the questions and bring in their knowledge from biology and chemistry where relevant. (Guidance for facilitating these activities are similar to those given for facilitating University of Washington-style Tutorials. See for example, Facilitating in Tutorials from the UMd-PERG.)



Some of our homework problems have also been successfully used in small group problem solving and discussion. In particular, the following pair makes a good 50 minute group session.





Quizzes and Exams:


Quizzes are intended as formative assessment, not summative. It is intended for these to be challenging and for there to be potentially extended discussions about the answers when they are handed back. Exam questions are intended as summative. A few sample questions and formatting are provided here as document files for easy cutting and pasting into a printed quiz or exam. (Use of these files are limited to faculty. Please contact Joe Redish for access.)







The first semester laboratory for the University of Maryland's NEXUS/Physics is essentially all about random motion. It uses powerful microscopes and video capture technology to study the difference between directed and random motion. The lab begins with an activity examining videos of cell motion, follows with a study of the motion of a macroscopic object through a fluid and terminal velocity, and follows with microscopic observations of micron sized beads in a fluid. The lab sequence is finished with a capstone experiment in which students observe tubules inside a living onion skin cell and study their motion and what it can tell about the internal workings of a cell.


The labs are Scientific Community Labs in structure — set up to be "data rich" and "instructions thin". Instead of students being given detailed instructions to make certain they wind up with a particular result, they are given a question to answer and powerful tools with which to explore it. The labs are challenging and encourage students to think about what they are doing and why, and to require them to develop a good conceptual understanding of the physics going on. Many labs are two to three two-hour sessions and the students work cooperatively in groups of four.


The labs and instructions for delivering them can be found at the link below.



A published paper describing the development of the labs can be found below.





Joe Redish 12/27/17


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