IT'S A SCIENTIFIC FACT
'(<a href="http://www.j-archive.com/media/2011-07-06_DJ_14.wmv">Here is the clue. Pay attention to Sarah.</a>) Chairs, a broom, some string, and a can full of sand are all you need for the experiment that creates one of these swinging devices, similar to the one physicist Foucault used to show the earth's rotation'
a pendulum