A Laboratory Exercise To Teach The Hydrostatic Principle As A Core Concept In Fluid Mechanics

Every field of study has core concepts that are essential to the understanding of the material. Students must understand these concepts and use them as a foundation for further study in the field. Most students carry preconceived ideas based on previous life experiences into the classroom which may conflict with the concepts being taught. These misperceptions can be difficult to overcome. It is common for students to take the material presented in a lecture and try to reconcile the new information with their preconceived ideas. This creates problems for both the instructor who is trying to instill these core concepts and the students who struggle with the conflicts. One approach to overcome these problems is to create a laboratory experience that will help the students to face their misperceptions and replace them with the appropriate core concept. The authors are currently investigating this approach as it relates to the fluid and thermal sciences. One of the key core concepts in the area of fluid mechanics is the hydrostatic principle relating the pressure in a fluid to the depth of the fluid. A common misperception is that the pressure is a function of the weight of the fluid above the point of interest when it is actually a function of the depth of the fluid column. This paper describes a laboratory exercise designed to teach this concept to the students. While a description of the apparatus and the test will be included, the focus of the paper will be on some of the results of the exercise to date, qualitative conclusions based on observing the exercise, and some suggestions for further refinements of the exercise. The assessment data which is discussed in the paper tends to indicate that students do not have a hard time comprehending the basic principle but do run into difficulty when trying to apply their understanding to practical problems. The laboratory exercise has been used during three different courses covering Mechanical Engineering, Civil Engineering, Mechanical Engineering Technology and Electrical Engineering Technology students at both Penn State Erie and Portland State University. Different assessment tools were used each time the exercise was run since they were being developed and modified during that time. Each time the results related to applications have been similar. This is discussed in the paper.