Edwin F. Greco

Thermocapillary migration of interfacial droplets

We study the thermocapillary driven motion of a droplet suspended at an interface of two fluid layers subjected to an imposed temperature gradient parallel to the interface. We compute the temperature and velocity fields inside and outside of the droplet using a boundary collocation numerical scheme in the limit of small capillary and thermal Peclet numbers and compare the results with the classical problem of thermocapillary migration of a droplet in the bulk. In particular, we find that, for typical values of parameters, interfacial droplets migrate in the direction opposite to the temperature gradient, while in the classical problem migration is always in the direction of the gradient. Furthermore, we find that a rich variety of flow structures can emerge inside interfacial droplets. We also confirm that for parameters matching a recent experimental study of mixing inside interfacial microdroplets [R. O. Grigoriev, V. Sharma, and M. F. Schatz, Lab Chip 6, 1369 (2006)] the interior flow can be approxima...

Comparing large lecture mechanics curricula using the Force Concept Inventory: A five thousand student study

The performance of over 5000 students in introductory calculus-based mechanics courses at the Georgia Institute of Technology was assessed using the Force Concept Inventory (FCI). Results from two different curricula were compared: a traditional mechanics curriculum and the Matter & Interactions (MI the differences between curricula persist after accounting for factors such as pre-instruction FCI scores, grade point averages, and SAT scores. FCI performance on categories of items organized by concepts was also compared; traditional averages were significantly higher in each concept. We examined differences in student preparation between the curricula and found that the relative fraction of homework and lecture topics devoted to FCI force and motion concepts correlated with the observed performance differences. Concept inventor...

Do-It-Yourself Whiteboard-Style Physics Video Lectures

Video lectures are increasingly being used in physics instruction. For example, video lectures can be used to “flip” the classroom, i.e., to deliver, via the Internet, content that is traditionally transmitted by in-class lectures (e.g., presenting concepts, working examples, etc.), thereby freeing up classroom time for more interactive instruction. To date, most video lectures are live lecture recordings or screencasts. The hand-animated “whiteboard” video is an alternative to these more common styles and affords unique creative opportunities such as stop-motion animation or visual “demonstrations” of phenomena that would be difficult to demo in a classroom. In the spring of 2013, a series of whiteboard-style videos were produced to provide video lecture content for Georgia Tech introductory physics instruction, including flipped courses and a MOOC. This set of videos (which also includes screencasts and live recordings) can be found on the “Your World is Your Lab” YouTube channel. In this article, we de...

Peer Assessment of Student-Produced Mechanics Lab Report Videos.

We examine changes in students’ rating behavior during a semester-long sequence of peer evaluation laboratory exercises in an introductory mechanics course. We perform a quantitative analysis of the ratings given by students to peers’ physics lab reports, and conduct interviews with students. We find that peers persistently assign higher ratings to lab reports than do experts, that peers begin the semester by giving high ratings most frequently and end the semester with frequent middle ratings, and that peers go through the semester without much change in the frequency of low ratings. We then use student interviews to develop a model for student engagement with peer assessment. This model is based on two competing influences which appear to shape peer evaluation behavior: a strong disinclination to give poor ratings with a complementary preference to give high ratings when in doubt, and an attempt to develop an expertlike criticality when assessing peers’ work.

Exploring physics students’ engagement with online instructional videos in an introductory mechanics course

The advent of new educational technologies has stimulated interest in using online videos to deliver content in university courses. We examined student engagement with 78 online videos that we created and were incorporated into a one-semester flipped introductory mechanics course at the Georgia Institute of Technology. We found that students were more engaged with videos that supported laboratory activities than with videos that presented lecture content. In particular, the percentage of students accessing laboratory videos was consistently greater than 80% throughout the semester. On the other hand, the percentage of students accessing lecture videos dropped to less than 40% by the end of the term. Moreover, the fraction of students accessing the entirety of a video decreases when videos become longer in length, and this trend is more prominent for the lecture videos than the laboratory videos. The results suggest that students may access videos based on perceived value: students appear to consider the laboratory videos as essential for successfully completing the laboratories while they appear to consider the lecture videos as something more akin to supplemental material. In this study, we also found that there was little correlation between student engagement with the videos and their incoming background. There was also little correlation found between student engagement with the videos and their performance in the course. An examination of the in-video content suggests that students engaged more with concrete information that is explicitly required for assignment completion (e.g., actions required to complete laboratory work, or formulas or mathematical expressions needed to solve particular problems) and less with content that is considered more conceptual in nature. It was also found that students’ in-video accesses usually increased toward the embedded interaction points. However, students did not necessarily access the follow-up discussion of these interaction points. The results of the study suggest ways in which instructors may revise courses to better support student learning. For example, external intervention that helps students see the value of accessing videos may be required in order for this resource to be put to more effective use. In addition, students may benefit more from a clicker question that reiterates important concepts within the question itself, rather than a clicker question that leaves some important concepts to be addressed only in the discussion afterwards.