Online Google Dictionary

archimedes principle wordnet sense
  1. In physics, buoyancy is an upward acting force, caused by fluid pressure, that opposes an object's weight. If the object is either less dense than the liquid or is shaped appropriately (as in a boat), the force can keep the object afloat. ...
  2. Any object wholly or partly immersed in fluid will be buoyed up by a force equal to the weight of the fluid displaced by the object.