Measuring the vertical gradient of gravity
Summary
The free-air effect tells us that as elevation above sea level increases, gravitational acceleration g decreases at the rate of about 0.3086 mgal/meter. This effect is routinely corrected for when making gravity surveys. We will use the LaCoste & Romberg gravimeter to measure the free-air effect in a tall building on campus, and compare with the theoretical value.
keywords: gravity; vertical gradient; gravimeter
keywords: gravity; vertical gradient; gravimeter
Context
Audience
undergraduate elective course in geophysics
Skills and concepts that students must have mastered
follow instructions to use an expensive and delicate instrument
use a spreadsheet to tabulate, graph and analyze numerical data
use a spreadsheet to tabulate, graph and analyze numerical data
How the activity is situated in the course
As a two-week lab exercise, one week for measurement in small groups, and one week for analysis
Goals
Content/concepts goals for this activity
effects on gravitational acceleration
Higher order thinking skills goals for this activity
analysis of data acquired
formulation of hypotheses why experimental value may not agree with accepted value
consideration of accuracy, precision, and replicability of results
formulation of hypotheses why experimental value may not agree with accepted value
consideration of accuracy, precision, and replicability of results
Other skills goals for this activity
writing of lab report in scientific paper format
operating analytical equipment
working in groups to collect data and interpret results
operating analytical equipment
working in groups to collect data and interpret results
Description and Teaching Materials
Vertical gradient of gravity lab handout (Microsoft Word 2007 (.docx) 19kB Apr30 12)
Teaching Notes and Tips
Needs a gravimeter
Data must be reviewed by instructor and errors parsed, especially if data are to be shared among groups
Data must be reviewed by instructor and errors parsed, especially if data are to be shared among groups
Assessment
Writeup of lab report in scientific paper format