From Wikipedia:  A Rube Goldberg machine, device, or apparatus is a deliberately over-engineered or overdone machine that performs a very simple task in a very complex fashion, usually including a chain reaction. The expression is named after American cartoonist and inventor Rube Goldberg (1883-1970).

The girls designed elaborate, comical machines using pulleys, levers, dropping marbles, planes, inclines, fulcrums – you name it and they used it!