Salt Lake City, Utah
June 23, 2018
June 23, 2018
July 27, 2018
Experimentation and Laboratory-Oriented Studies
BYOE: Activities to Map Intuition to Lumped System Models
Abstract The objective of this series of experimental activities is to create a stronger qualitative connection between observed behaviors of simple systems and the equations, terminology, and graphical methods used to describe and represent them. This work is motivated by an observed inability of students to qualitatively model and predict how a real-life system will behave, despite an understanding of such models in homework and lecture settings. Thus, there is a disconnect between understanding how real-life physical behaviors map to the elemental and system equations of idealized models. The experiments and corresponding qualitative discussion among peers are designed to precede and pair with subsequent course discussion of the concepts involved. During the follow-on lectures, the instructor references, and may repeat, these demonstrations to link the student’s observations to the appropriate terminology, equations, and graphical representations being taught. The four short experiments presented in this paper are described briefly below; a selection of these activities will be demonstrated at the ASEE conference.
Canoe Coast-down: Students study video taken of a canoe in “coast-down”, as its velocity decays. The canoe exhibits a first-order response to this initial condition. Students hypothesize models for their observations, and thus begin developing the skill of system identification. During a subsequent class the instructor leads the students through a more complete analysis.
Playdough Hot Potato: Students are given playdough that represents a “hot potato” and asked to come up with ways to make it cool down as fast as possible. In a follow-on lecture the instructor introduces the parameters of thermal resistance, thermal capacitance, time constant, and step input size; and links the cooling methods proposed by students to the corresponding parameter(s). The open-ended rich solution set of this challenge offers to open discussion in many directions, including the limitations of lumped system modeling.
Fluid in a Tube: This experiment illustrates the step response of a second order fluid system as a function of its damping ratio. Students are asked to observe fluid oscillations in a tube and explore how the size and duration of oscillations varies with restrictions to air flow at the end of the tube. During a follow-on lecture the instructor shows plots of the oscillations observed in this activity for both high and low damping ratios. This provides a lead-in for more extensive discussions on the characteristics and behavior of second order systems.
Slinky and Mass: A small mass attached to a mini-slinky forms a simple spring-mass system which is used to map the observed time domain response of a minimally damped second order system to the graphical representation of its frequency response. Students move one end of the spring up and down, observe the response of the mass on the other end, and qualitatively describe the system behavior for a range of frequencies.
White, R., & Levey, C. G., & Ray, L. (2018, June), BYOE: Activities to Map Intuition to Lumped System Models Paper presented at 2018 ASEE Annual Conference & Exposition , Salt Lake City, Utah. https://peer.asee.org/30168
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