Buoyancy

2.3.0    Buoyancy:

    When an object is immersed in a fluid, such as a li quid, it is buoyed UPWARD by a force called the BUOYANT FORCE. When the object is placed in fluid is DISPLACES a certain amount of fluid. If the object is completely submerged, the VOLUME of the OBJECT is EQUAL to the VOLUME of FLUID it displaces.

2.3.1 Archimedes’s Principle:

An object is buoyed up by a force equal to the weight of the fluid displaced.

2.3.2 Stability:

           A floating body as in Fig.27 may not approve of the position in which it is floating. If so, it will overturn at the first opportunity, and is said to be “unstable”, like a pencil balanced on its point. The way to make sure whether a floating body is stable is to disturb the body slightly and see if it develops a restoring moment that will return it to its original position. If so, it is “stable”; if not, “unstable”.

2.3.3 Floating Bodies:

                     Here we’ll consider transverse stability. In actual applications both transverse and longitudinal         stability are important.

The center of buoyancy (centroid of the displaced volume) shifts laterally to the right for the case shown because part of the original buoyant volume (wedge of emersion) is transferred to a new buoyant volume (wedge of immersion).

The point of intersection of the lines of action of the buoyant force before and after heel is called the metacenter M and the distance GM is called the metacentric height. If GM is positive, that is, if M is above G, then the ship is stable; however, if GM is negative, the ship is unstable.