Although this may be better digested by a high school crowd, the metaphor that this instructor uses to simulate space-time is extremely visual. I would LOVE to have this in my classroom one day. In the video, Mr. Burns simulates how masses are gravitationally attracted to each other, why smaller objects orbit larger objects, why the planets are moving in the same direction around the Sun and how the moon can orbit the Earth, whilst also orbiting the Sun. Should someone physically recreate this metaphor in their room, I think that it would satisfy most of, if not all, the requirements for an effective metaphor.