First up is the Merry-Go-Round:
This model you put together and the gears operate the spinning discs! A nifty demonstration of cetripital force!
Next up is the Clock
This is not an operational clock, but it does show how gears are used so that the hour hand moves as you rotate the minute hand. An excellent demonstration of gear ratios!
Next we have the Koontz Safe
Here you build the safe and set the combination lock. Then you can see how you need to turn the dials just right to open the lock!.
Finally, getting back to the world of optics, we have the Periscope!
With the included two mirrors and the frame you build you can construct a device that lets you see over walls, around corners and other locations! See without being seen!