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St. Matthew's School

Background Essay

Buoyancy is the tendency of an object to float in a fluid. Buoyancy is controlled by differences in density between the object and the fluid. Salt water is more dense then fresh water so an object will float higher in salt water then in fresh water. Objects that float are positively buoyant. Objects that sink are negatively buoyant. An object that neither floats nor sinks is neutrally buoyant. Archimedes who was a Greek mathematician found the idea of buoyancy. Archimedes Principles is as follows: Any object, wholly or partly immerses in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object. Whether an object floats or sinks is based on the weight of the object and the amount of water it displaces or moves.

A buoyant force is evident in several places for example what keeps a hot air balloon in the air or a ship from sinking. Certain objects are more buoyant then others. When you dive you do not want to float to the surface, people or objects that float are positively buoyant. Some people are to heavy and sink, they are negatively buoyant. People have been using buoyancy for centuries. Prehistoric people who built rafts used buoyancy to keep themselves from swimming. Using neutral buoyancy of air is what a hot air balloon depends on to work. Displacement is used frequently when talking about buoyancy. When an object displaces a fluid it is basically pushing the fluid out of the way. Objects with a large volume displace more water. The more fluid an object displaces the more buoyant that object will be. This is why buoyancy is a lot more important then weight.

An extremely heavy object like an ocean liner must displace the same amount of water as the weight of the ocean liner. If the ocean liner weighs 100 tons it must displace 100 tons of water. If it weighs 100 tons but it only displaces 90 tons of water the boat will sink. Many objects that float in fresh water will not float in salt water so you must test objects before going into the ocean. Salt water has salt diluted into it so it weighs a little more than fresh water. One of the most important skills for a diver to master is neutral buoyancy. If all you have is negative buoyancy you will sink to the bottom of the sea. If all you have is positive buoyancy one you may never sink or if you do get under you will rise to the surface so fast that you will get the BENDZ or you lungs will explode if you hold your breath.

Divers in order to keep neutral buoyancy are required to have weight belts to sink and BCD's. BCD stands for Buoyancy Control Device. This can be inflated and deflated to sink or to rise to the surface or stay neutrally buoyant. When neutrally buoyant divers can do many functions underwater easier. Buoyancy is essential to all areas of diving. Without buoyancy diving would not be possible. A good diver must be able to understand buoyancy and learn to use it through the BCD. Buoyancy is a very important aspect to maritime life.