As a parent of an energetic child of 2+, other than the interrupted sleep schedule, I get to spend a lot of time in playgrounds, watching Vanessa sliding on the slides and swinging on the swings. From one point of view it is a total waste of time for the parent who'd prefer a more productive pastime (e.g. completing the next xplorer² upgrade). However a restless mind can find stimulation in the most unlikely places. So you start wondering how fast is a swing swinging, and does the size of the child matter at all? If you put 2 kids swinging side by side, will they synchronize?
The pendulum is a simple machine with great history, but for the life of me I can't remember being taught about it in school. Perhaps the calculus involved is too hard for high school but considered too plain for college. So it gave me great pleasure discovering a short article on the period of a simple pendulum.
It combines simple first principles physics with experimental derivation that even a "mature" student can follow. In just 2 pages it answered all my questions on swings: you can't move a kid faster by swinging harder; you won't change much feeding your kid more lard to fatten it; but you can make a rough grandfather clock out of it <g>. Thanks Galileo Galilei!