This lab uses one of the excellent online simulations at PhET: http://phet.colorado.edu
From the PhET site: "In order to help students visually comprehend these concepts, PhET simulations animate what is invisible to the eye through the use of graphics and intuitive controls such as click-and-drag manipulation, sliders and radio buttons. In order to further encourage quantitative exploration, the simulations also offer measurement instruments including rulers, stop-watches, voltmeters and thermometers. "
The sims are free to use, run on Mac, PC, and Linux platforms, can be downloaded to run locally (in the case of no or slow internet).
This mostly inquiry-based lesson/lab allows students to investigate the effects of mass and velocity on an orbiting satellite (planet). Students will increase and decrease mass, increase and decrease velocity in both the x and y plane, make predictions and then compare their predictions to actual results. Covers concepts of velocity (speed AND direction), and mass and their effect on orbital motion.
Other lesson plans are available at the PhET site; this 5 page lab was adapted drastically to make it more appropriate for 7th - 9th grade classes.
zip file contains both a .doc and a .pdf