The wobbly table problem
Stories from Physics for 11-14 14-16
A physicist working in the CERN café became frustrated with its wobbly tables and began to study their stability. André Martin found that it was always possible to rotate the table so that all four legs stood firmly on the ground. He later published a proof that, for a square table with four legs on irregular ground, an equilibrium state can be found by rotation through an angle of less than 90°.