Archive for April, 2012
Archimedes’ Principle is a law of physics stating that the upward buoyant force exerted on a body immersed in a fluid is equal to the weight of the fluid the body displaces. In other words, an immersed object is buoyed up by a force equal to the weight of the fluid it actually displaces.A practical example of this principal in action is the use of Lift Bags to recover sunken objects such as boats, anchors, motors and antiquities.
Check out the video below of a snowmobile retrieved by Atlantis Diving Ltd of Alberta, Canada, when it went through the ice. This clip illustrates the use of a 250lb lift bag to bring the snowmobile to the surface, with the help of an additional 75lb lift bag on the back. The snowmobile was running again in two days after all the water was drained out. You can see the lift bags sliding along the underside of the ice surface.
A Lift Bag is an item of diving equipment consisting of a robust and air-tight bag with straps, which is used to lift heavy objects underwater by means of the bag’s buoyancy. The heavy object can either be moved horizontally underwater by the diver or sent unaccompanied to the surface.
A Lift Bag works by displacing water inside a flexible container with a pressure slightly exceeding the surrounding water. This creates a ‘hole in the water’ with a buoyancy equal to the volume of water displaced. A lift bag going down is compressed and provides decreasing buoyancy while a bag coming up expands and provides increasing buoyancy. This is a practical example of Archimedes’ Principle in action.