Measuring the Earth with Traceroute
  The traceroute utility on any computer connected to the Internet can be used to record the roundtrip time for small Internet packets between major Internet traffic hubs. Some of the routes include transmission over transoceanic fiber optic cable. We report on traceroute's use by students to quickly and easily estimate the size of the Earth. This is an inexpensive way to involve introductory physics students in a hands-on use of scientific notation and to teach them about systematics in data. 
Snowflake Kicovic, Loren Webb and Michael Crescimanno (Department of   Physics and Astronomy, Youngstown State University)