Apparatus Competition

2007 AAPT Summer Meeting

Greensboro, NC

A simple apparatus for use in determining the diameter and location of a hidden circular cavity

A. James Mallmann

Department of Physics and Chemistry

Milwaukee School of Engineering

1925 North Broadway

Milwaukee, WI 53202-3109

414-277-7317

mallmann@msoe.edu

Abstract

This simple, inexpensive apparatus, easily constructed using three sheets of fiberboard, is designed to challenge students to accomplish two goals:

· The easier goal is to determine the diameter of a hidden circular cavity.

· The more challenging goal is to determine the location of the center of the hidden circular cavity.

Construction of Apparatus:

The three-layer sandwich of one-eighth or one-fourth-inch

thick fiberboard sheets shown here

is fabricated by gluing together three identically shaped sheets shown in the lower portion of the photo.

The apparatus will include a single sheet of the fiberboard for use in determining the density of the material.

Use of Apparatus:

This apparatus will be used by students for the first time during the fall of 2007. We believe that the use of the apparatus by students will have several advantages:

• The experimental challenge will be to determine facts about the size and location of a circular cavity that is not visible and for which no direct measurements can be made. This is similar to problems associated with the indirect analysis of data for medical diagnostics, engine analysis, and problems in astronomy.
• The students will be expected to determine what needs to be measured and how to analyze the experimental data to accomplish the goals of determining the diameter of the circular cavity and the location of the center of that circular cavity.
• Achieving the goals of the experiment requires an understanding of the concepts of density and center-of-mass.
• Unlike many introductory experiments that involve the determination of a well known quantity like g or e/m, this experiment involves a true unknown. They will not be able to find the answer on the internet.
• The experiment is appropriate for high school students or college students.

Equipment and costs required to construct apparatus:

Item	Source	Part number	Cost
Fiberboard	Lumberyard or hardware store	-	<$1.00
Ordinary carpentry tools
Total Cost			<$1.00