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Main Menu Session 1815

Hands-On Demonstrations in Introductory Mechanics

J. Ledlie Klosky and Reid Vander Schaaf United States Military Academy at West Point

Introduction Students often have difficulty grasping the reality of what is being discussed in introductory courses in mechanics. For some students, especially those who are struggling, physical reality becomes mired in seemingly endless equations and the apparent mish-mash of theory and practical application. This should be prevented if at all possible, as mechanics is the first course in which students can participate in designs that include material type and geometry in a realistic way. One essential method of convincing students of the importance and truth of what you are teaching is to actually show them that truth up close. Student feedback gathered during and after the semester consistently reinforces the effectiveness of hands-on demonstrations in driving home key points in mechanics.

This paper presents several simple, low-cost and rapid classroom demonstrations that enhance student understanding by allowing for the direct observation of physical phenomenon. Included here are demonstrations of shear, stress transformation, pressure vessels, and statically indeterminate systems. Each of these demonstrations has been thoroughly classroom-tested, and comments on the use of each demonstration are presented.

Conversion of Force and Stress Objective: To clearly show the relationship between force, area and stress, while simultaneously demonstrating a key mechanical concept; the pressurized cylinder and piston system.

Equipment: The equipment required for this demonstration is shown in Figure 1. While somewhat more costly and complex than the other systems presented in this paper, the total cost for materials is still less than $250. Some machining is also required. The device consists of a 3 ft acrylic tube having an inside diameter of 3 in, capped at each end with a threaded PVC cap. The top cap has a hole for the pushrod, and the bottom cap has an access port to which a 15 psi pressure gage and bleeder valve is attached. Additionally, the top of the half-inch pushrod is fitted with a load platform. The bottom of the pushrod is fitted with a soft rubber wiper. Initially, a tight-fitting reinforced hard-rubber wiper was contemplated, but the friction from the wiper-cylinder interface was too large and ruined the demonstration. The relatively light friction from the soft rubber wiper should be balanced with the weight of the platform and pushrod assembly, so that the added weight on the platform directly converts to the pressure seen on the gage. A portable scale with a capacity of about 100 lbs is also useful, and a calibrated bathroom scale will serve this purpose nicely.

Proceedings of the 2002 American Society for Engineering Education Annual Conference & Exposition Copyright 2002, American Society for Engineering Education

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Vander Schaaf, R., & Klosky, J. L. (2002, June), Hands On Demonstrations In Introductory Mechanics Paper presented at 2002 Annual Conference, Montreal, Canada. 10.18260/1-2--10783