This demonstration was voted 2nd in the Best Demo Competition at the British Interactive Group (BIG) Event held in Manchester from 26th-28th July 2006.
The picture on the right is a still from a Quicktime movie of the demo (about 1 MB). Before you watch the movie, take it from me that the only thing joining the 4 white beams is a very thin and flexible piece of ribbon. Each beam simply hangs from the one to the left of it. You'd expect that when I push the whole assembly off the end of the table, it would dangle down. Instead, it dangles up! Watch the movie to see it in action.
Of course, this is not an anti-gravity machine. In fact, it's gravity that pulls the beams up against your expectations. If you look carefully, you'll see that each beam (which is a very light tube of paper) has a pair of counterweights attached to it. The arms holding the counterweights are particularly obvious on beam A. The counterweights cause this beam to balance pointing upwards as it dangles from beam B. In its turn, beam B has counterweights large enough to make it point upwards as it dangles from beam C, even though it has to support the weight of beam A. The counterweights on beam C are even larger, to make it balance pointing upwards as it dangles from beam D, even though it is supporting the weight of beams A and B. Beam D has the largest counterweights, so that it balances pointing upwards even though it supports the combined weights of beams A, B and C.
How can I claim that gravity pulls the beams up? Although the most visible parts of the whole assembly move upwards as I slide it off the table, its centre of mass has actually moved downwards relative to the point of support (my hand). Most of the mass is concentrated in the inconspicuous counterweights on beam D. This is true also of any subsection of the assembly. For example, most of the mass of beams A and B is concentrated in the counterweights on beam B, and the centre of mass of these two beams moves downwards relative to the support (the end of beam C) as they assume their final position.