Gear train
Imagine the three circles in the left hand panel to be three meshing gears.
You can animate the entire gear train by clicking on the icon in the lower left hand corner.
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?