This model uses the electrically operated blackboards in the physics lecture halls to model a focal plane shutter.
Move the rear board to its lowest visible position and move the front board out of sight (down). Now start the rear board moving up; this is the shutter opening. Then start the front board up; this is the shutter closing. If you allow the rear board to get to the top before you start the front one, this illustrates how the shutter works at slow shutter speeds. If you start the front board up before the rear one gets to the top you simulate faster shutter speeds. Stop the boards when the entire area is covered. Move them back down together to show how winding works to reset the shutter.For obvious reasons, this demonstration is only feasible in the large Physics lecture halls.