Billiard-Ball Computing is a pretty fun computation model based on newtonian mechanics.

Dunno if it's a bit hard as a project, but for example explaining a little why reversible computation is interesting (make sure you mention Landauer's Principle: basically, erasing information increases the temperature of the system, and this cannot be avoided), then showing a simulation of, say, an And gate (you can find a pretty good simulator here as a java applet, you could do some other gate too but they can get seriously tricky) could already make for a really cool presentation, and I at least would be perfectly willing to consider the computer simulation as an "experiment" - but otherwise, implementing an "and" gate for reals should be also possible.