by Raymond Alexander Kukkee

Created on: July 21, 2008   Last Updated: November 19, 2011

 Why do things Float?

Buoyancy is partially responsible for the ancient art of naval warfare, the floating of the simplest wooden raft in back yard ponds, and the sailing of the largest ocean liners in the world. Lack of buoyancy caused the greatest oceanic disaster in history, the sinking of the Titanic. Buoyancy also saved individual lives in the same tragic incident, as a few lucky survivors not only observed, but participated in. What is buoyancy?.

Buoyancy is the tendency or ability of any object to float in a liquid, or rise in a gas. It is a curiosity that the materials involved do not themselves create buoyancy. Steel sinks in water, yet a steel-hulled ocean liner floats easily. A concrete block sinks, but cement-hulled yachts float elegantly. Some individual people can float, while others sink. Why? Let us examine the physics behind the phenomenon known as buoyancy.

Each individual material in the universe has mass and volume. When mass and volume are expressed in a ratio, the concept of specific gravity is created. What is specific gravity? Specific gravity is an international standardized measurement of weight (or mass) per unit of volume, usually expressed as compared to that of water . Each cubic centimeter (c.c.) of water weighs 1.0 gram. A metal that weighs 5 grams per cubic centimeter and is 5 times heavier than water would therefore have a specific gravity of 5.0 and sink quickly in water-a lack of buoyancy.

It is the physical characteristics of mass and specific gravity and the resultant differential between the specific gravity of different materials that really causes the phenomenon known as buoyancy, or floating. As Archimedes principle may be paraphrased, when an object is placed into water, the buoyancy provided by the water is precisely the weight of the volume of water displaced, regardless of the shape of the object. Archimedes was reported to have said " Eureka!" when he made that discovery, and no wonder, for it is an amazing concept.
In simple, practical application, if the weight of an object exceeds the weight of the water it displaces, the object will sink. If lighter, it will float.

Let us examine what actually causes buoyancy. When an object of any shape and specific volume is placed in water, it attempts to displace exactly the same volume of water. Coincidentally, the weight of the water displaced equals the weight of the object. The weight of the water displaced  provides buoyancy, or flotation for the object,

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