Thursday, February 13, 2014
StimulusA news bulletin about a prototype device surprised me today, describing the device as a "handheld cell counter the size of a Rubik’s Cube," then as "a simple, solid-white cube measuring 2x2x3 inches". (my emphasis).
It is dismaying to observe that cube may be following literally in the path to uselessness, if a cube no longer has to be cubic. That is, as every schooled person ought to know, a "regular polyhedron having six identical square faces."
What should have been said is a block, or a cuboid, or--my preference--a square cylinder.
- A block, I think most would agree, is rectangular but not necessarily square on any side. It may be a bit oblong, like a brick. It may be, as Wiktionary notes, "approximately cuboid." But what is cuboid?
- A cuboid is a rectangular parallelepiped, of which the cube is the special case where the rectangular faces are congruent squares. The cuboid generalizes the cube by allowing the edges to lengthen or shorten as long as the opposing faces remain parallel to each other. The cube might be flattened and stretched to become brick-like: a little longer than twice the width, and wider than it is high (240 × 115 × 71 mm, e.g.). Or, it might extend a two inch cube to a 2x2x3 inch cuboid.
- Whereas a cylinder may usually be circular (and right) in non-mathematical usage, it may be any "surface created by projecting a closed two-dimensional curve along an axis intersecting the plane of the curve." (source: Wiktionary). A dowel is a cylinder and, yes, one can buy square dowels (ask your search engine).
ConclusionIf the three-dimensional rectangle has edges of more than one length, i.e. one cannot say it is a some length cube but must say it is a width by depth by height something, it is not a cube.
ReferencesA 'game-changer' for HIV/AIDS -- UC Berkeley College of Engineering