Buoyancy As Expressions Of Pj Problems
Peter Oye Sagay
The Earth's surface is mostly water and its atmosphere is an invisible mixture of gases (mostly nitrogen and oxygen) called air. Water and air belong to the group of substances called fluids (substances like liquids and gases that flow and take the shape of their containers).
An object placed in a fluid experiences an upward force of the fluid that act against the weight of the object plus the weight of the fluid above th object. This force is called the buoyant force and the phenomenon is called buoyancy. The great mathematician Archimedes of Samos (born about 287BC) discovered the method for determining the buoyant force. This method is known as the Archimedes Principle: the buoyant force on an object is equal to the weight of the fluid displaced by the object. An object placed in a fluid floats when its weight is less than or equal to the buoyant force. This condition for floating is also stated in terms of density: an object floats in a fluid if the density of the object is less than the density of the fluid. If the weight of a submerged object is exactly equal to the buoyant force (weight of the volume of fluid displaced by the object), the object will float at a constant depth. The buoyant force plays an important role in the motion of objects in fluids. For example, the volume of the gas-filled bladder of most fishes changes inorder to adjust to the buoyant force at various depths. Similarly, submerged submarines take on or discharge sea water to adjust to the buoyant force at various depths. The hot-air balloon pilot matches the buoyant force of air by adjusting the weight of the hot-air balloon.
The fluid, the object placed in the fluid, the weight of the volume of fluid displaced by the object and the buoyant force are all Pj Problems. Therefore, buoyancy is an expression of Pj Problems.