Measuring the Gravity Field: "The Stairwell Lab"

Samuel T. Peavy
Georgia Southwestern State University
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This lab teaches the student how to use a gravimeter by measuring gravity in a stairwell. A plot of the data set will yield and estimate of the elevation correction.

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Undergraduate geophysics course
Designed for a geophysics course

Skills and concepts that students must have mastered

They must be able to do simple mathematical calculations (algebra) and make a simple graph, fit a line to their data and find the slope.

How the activity is situated in the course

This exercise is usually used to introduce the function of the gravimeter to the students.


Content/concepts goals for this activity

Introduction to using a gravimeter; making measurments and accurately recording the data.

Higher order thinking skills goals for this activity

Analyzing the data for drift and correcting it; plotting the resulting gravity value vs. elevation; finding the slope and comparing their value to the elevation correction.

Other skills goals for this activity

They must work with a their fellow students to collect the data, then analyze the results and write a report for a grade in the course. There are two follow-up labs where the knowledge they gain on the use of the meter is critical to their success.

Description of the activity/assignment

Students will prepare for the lab by reading a description of gravity meter operation. After a brief quiz, the students will assemble with the meter in the stairwell of the building and measure the elevation to each level. After this, they will take multiple measurements on each level going up the stairwell, and then repeat the measurements on the way down, making sure to record the data values and the time. They will then convert the raw data to mGal using the conversion factor from the meter, and then use the data from the lower level to correct for drift. The corrected data are then plotted vs. elevation, a slope determined and the slope compared to the elevation correction term. The students will then write a lab report describing the procedure, presenting the data and their analysis, example calculations and their results.
Has minimal/no quantitative component

Determining whether students have met the goals

I read over the lab reports to make sure they have understood the assignment a correctly analyzed the collected data. I then assign a grade based upon how well they have done. I don't look so much at the final answer, but more at the procedure - a calculator (or their fingers!) can malfunction, but if they understand meter operation well enough to collect good data and can analyze it properly, I think the goals for this lab are met.

More information about assessment tools and techniques.

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Supporting references/URLs

This is the web site I started for this class before 15-contact hours a week bogged me down:

I reference them to a link to John Louie's web page on how to use a Worden gravimeter.

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