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Links
[1] http://galileo.rice.edu/index.html
[2] http://astro.unl.edu/classaction/
[3] http://www.teachersdomain.org/resource/phy03.sci.ess.eiu.galMoon/
[4] http://www.teachersdomain.org/resource/phy03.sci.phys.mfw.zweightlessness/
[5] http://www.teachersdomain.org/resource/phy03.sci.phys.mfw.freefall/
[6] http://phet.colorado.edu
[7] http://essp.psu.edu/sites/default/files/tes_esspissue.pdf