Buoyancy, inertia, the Stroop effect and other scientific laws and phenomena are explained with cranks, bubbling tubes and even a mechanical elephant at this hands-on science museum. Operated by the University of Wollongong, the Science Centre is very much geared towards kids (though adults might be pleased to learn how much they'd weigh on the planet Mercury). Planetarium shows ($6 extra) run regularly on most days.
You can get here on the free shuttle buses (55A and 55C) from Wollongong Station; they stop right outside.