Visit this site, from the U.S. Geological Survey, for an introduction to the motions of tectonic plates. You'll find descriptions of each of the four types of plate boundaries along with illustrations of the motions associated with each. The site also shows examples of each type of boundary, such as the San Andreas Fault in California.
6-8: 4C/M2a. Some changes in the earth's surface are abrupt (such as earthquakes and volcanic eruptions) while other changes happen very slowly (such as uplift and wearing down of mountains).
6-8: 4C/M11. The outer layer of the earth—including both the continents and the ocean basins—consists of separate plates.
6-8: 4C/M12. The earth's plates sit on a dense, hot, somewhat melted layer of the earth. The plates move very slowly, pressing against one another in some places and pulling apart in other places, sometimes scraping alongside each other as they do. Mountains form as two continental plates, or an ocean plate and a continental plate, press together.
9-12: 4C/H3. The outward transfer of the earth's internal heat causes regions of different temperatures and densities. The action of a gravitational force on regions of different densities causes the rise and fall of material between the earth's surface and interior, which is responsible for the movement of plates.
%0 Electronic Source %D May 5, 1999 %T Understanding Plate Motions %I United States Geologic Survey %V 2014 %N 30 September 2014 %8 May 5, 1999 %9 text/html %U http://pubs.usgs.gov/gip/dynamic/understanding.html
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