Archimedes’ Scale operates on the principle of buoyancy, submerging part of its body up to the appropriate line to measure the dry ingredients within.That is pretty darn brilliant.
Or how about the Principle of Communicating Vessels?
This principle states that the liquid levels in two “communicating” containers will stay at equal levels in both. By making use of this principle, these vessels keep potted flowers and cut flowers supplied with fresh water.And there's more amazing product designs from Acquacalda Designs on their site here!
Where were these when I was in grade school!? via