This is an odd concept I have tinkered with for a while.
It is a known fact that a string of dominos, or jenga bricks, or similar objects, when placed in a row, standing on their thinner 'ends', provided they are close enough together, can be knocked over simply by pushing the one at the end over. It will then cause the next one to fall, and that knocks the next one down, and so one, creating a visually pleasing way of spending time.
My idea is, that, given enough dominos and space, simple computers could be developed as such. Note that they would have to set again up after each calculation is made, which is a tedious process. To this end, I have already built and tested AND, OR, NOR, and NAND gates using a simple set of switches.
I think that the idea is possible, if not entirely reasonable. Although such computers would be almost useless, on the grounds that they would be huge and slow, it would be an interesting challenge for someone with too much time on their hands, or other suitable domino-placing apendage.
The stuff
Switches
The entire chain is built on a slightly raised platform, which must have quite a bit of depth. To make a switch, a gap is left in the platform, and another piece (I confess, I used toy bricks) is placed so as to slant between the platform, with one end at the bottom of the raised area on one side, and one balanced on the edge on the other platform. The clever part is, a 'signal', ie, a series of falling dominos, will only cross the switch in one direction (namely, uphill). So changing the switches position from slanting one way to slanting the other creates an 'off' or 'on' effect.
This is simple: two switches in a row, when both are set to 'on', there is an output.
Not quite so easy, this time the 'flow' of falling domino(e)s is split, and both pass over a switch, before they are rejoined and sent to the output. If either or both of the switches are 'on', then there is an output.
More complex...this time, the 'flow' is split once, then one branch is split again. The remaining branch curves a long way around to an output. The split branch is just an OR gate, as above. The split branches combine, as normal, then they cut across the path to the output. If either of the switches is on, there is no output, because the path to the output is cut in half by the other set of dominos.
This is very similar to the NOR gate, but the two switches are in series, so both need to be on in order for the output to be off.
note:my computer has developed a virus(hopefully not avian flu),so I can't download anything (filled all space). This means no ASCII stuff 'till I can download a converter for pictures.