12. COOLING TOWERS AND THE HYPERBOLOID OF ONE SHEET

Driving out of the township of Soweto in South Africa you pass two unusually decorated cooling towers. One carries an advertisement for the FNB Bank, the other, scenes from township life.

Mathematically, cooling towers are of interest because of their shape. If we take a hyperbola and rotate it about the axis it does not intercept, we obtain a solid of revolution called a hyperbola of one sheet. The towers demonstrate a truncated version. One of the most interesting properties of the hyperboloid of one sheet is that the curved surface contains two intersecting families of straight lines or generators which lie within the surface. Older viewers may remember the old wire waste paper baskets which illustrated this concept.

http://en.wikipedia.org/wiki/Hyperboloid