Teach the Earth > Geophysics > Teaching Activities > Free-Air Gravity

# Free-Air Gravity

Jeffrey A. Nunn
,
Louisiana State University
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This activity has benefited from input from faculty educators beyond the author through a review and suggestion process. This review took place as a part of a faculty professional development workshop where groups of faculty reviewed each others' activities and offered feedback and ideas for improvements. To learn more about the process On the Cutting Edge uses for activity review, see http://serc.carleton.edu/NAGTWorkshops/review.html.

#### Summary

Students use gravity measurements to estimate the height to the top of a platform in the Howe-Russell Attrium. This assignment is used to show the precision of gravity measurements and the Free-Air correction

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## Context

#### Audience

Designed for a geophysics course

#### Skills and concepts that students must have mastered

Gravity corrections for instrument drift, earth tides, latitude, and Free-Air

#### How the activity is situated in the course

A stand alone exercise

## Goals

#### Content/concepts goals for this activity

Estimate the height of a platform in the Howe-Russell Atrium using gravity measurement.

#### Higher order thinking skills goals for this activity

Students learn how to correct gravity data for instrument drift, earth tides, latitude, and free-air as well as how to deal with noisy data (as they collect the data)

#### Other skills goals for this activity

operating a gravimeter, learning the precision required in taking a gravity survey, working in a group

## Description of the activity/assignment

Students take a series of gravity measurements to estimate the height of the walkway near the top of the atrium in Howe-Russell. Students turn in a copy of the data sheet plus 1) an explanation of how they converted dial measurements to mgals; 2) plot of instrument drift/Earth tides correction; 3) estimate of elevation of the walkway using a Free-Air Correction; and 4) a brief (paragraph or two) discussion of potential errors in the survey.

## Determining whether students have met the goals

The laboratory exercise report is graded based on accuracy of calculations, correctly apply principles of instrument drift, earth tides, and Free-Air. The concluding essay is also help to see if students grasp how accurate gravity measurements can be and how important it is to take measurements and do corrections with a high level of precision.