Tuesday, April 04, 2006

Learn Kepler's Second Law with Satellite data

If you use the Union of Concerned Scientists satellite database you can do all sort of fun stuff with the data. For instance, Kepler discovered that the square of the period of a satellite would be inversely proportional to the cube of the long axis (or semi-major axis) of the orbit. Kepler only had planets to work with, we have our artificial satellites.

For circular orbits, the semi-major axis is just the radius of the orbit (don't forget to add the radius of the earth, 6378.1km, to the perigee to get the radius counted from the center of the earth). If Kepler had a bunch of satellite data to work with he might have discovered his second law even faster. Here it is demonstrated in this chart (click for a larger view)

Of course you need to understand Kepler's laws to be clever enough to launch a satellite into orbit in the first place, but it is a great example of learning with data how the physical law does apply.

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