Gear train

Imagine the three circles in the left hand panel are three meshing gears. You can move the entire gear train by dragging the large BLUE dot. [You can also animate the motion.] How are the radii of the three gears related? How are the angular velocities of the three gears related? How are the linear speeds of BLUE, YELLOW & GREEN dots related? How would you introduce the practical uses of gear trains to your students? What other questions could/would you ask of your students based on this applet?