Upwards-flowing water

by Marek Kordos


Seemingly Archimedes's screw is indeed Archimedes's invention. Its mathematical name - or rather that of its ideal model - is helicoid. This is a surface generated by a straight line uniformly rotating around a fixed axis orthogonal to it, and simultaneously sliding in a uniform and rectilinear way along the axis. If you replace the straight line by a segment meeting the axis at its midpoint, make the surface of sheet metal, choose a strong rod for the axis and place the whole thing within a tube, the device will pump water.

That's what it looks like, more or less.

You must place the axis at a slant and turn the crank fixed to it as if it were a hand-operated mincer. The water inside the tube will constantly stream down the sheet metal to compensate for the upwards-directed force due to rotation. It will not entirely succeed, so after some (how large) number of rotations, it will start overflowing at the top of the tube. This is how poor Egyptian peasants still pump the water from one irrigation channel to another.

If you don't believe in the efficiency of the device, try it with a spiral tube wound round the axis.