Measuring the Earth
University of Houston
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This page first made public: May 19, 2008
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With a colleague at the University of Kansas, we measure the size of the Earth using the method of Eratosthenese. This is handy because the UH and KU campuses are almost directly on a N-S line.
This is a demonstration I have done in Physical and Historical geology classes. Both are classes with mostly non-majors.
Skills and concepts that students must have mastered
How the activity is situated in the course
a stand alone exercise
Content/concepts goals for this activity
I want to demonstrate that simple measurements can be used to work out big problems. I also use the demonstration to illustrate the problems of precision vs. accuracy and the effect of error magnification. I have several students make the measurements with mm precision and then show how the differences in the values correspond to different final estimates of the size of Earth.
Higher order thinking skills goals for this activity
Other skills goals for this activity
Description of the activity/assignment
Because the campuses of the University of Kansas and the University of Houston are almost directly on a N-S line we can duplicate many aspects of the classic measurement of Eratosthenese in determining the circumference of the Earth. We use a web cast (backed up by cell phones) to communicate between the two campuses in real time. We measure the shadow of a 2 m stick in both locations at the same time and then go through the math required to calculate the size of the planet.
Determining whether students have met the goals
We don't do this during regular class time because it is best to do it near noon and because we have to coordinate between classes on different campuses. Therefore I don't think it is appropriate to require students to be present at the demonstration. However, to give credit to those that show up I as a question on the test that will be considered separately as extra credit.More information about assessment tools and techniques.
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