Buoyancy Explained: The Archimedes’ Principle

Buoyancy Explained: The Archimedes’ Principle

Greek mathematician, physicist, and engineer Archimedes of Syracuse suggested in his 250 BCE work “On Floating Bodies,” that any object, whether totally or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.

The infamous assertion made by the ancient Greek polymath is now known as the Archimedes’ Principle or the physical law of buoyancy. It essentially explains why certain objects float in a fluid and more specifically, why massive objects such as ships float despite their weight.

Buoyancy and Buoyant Force: On Floating Bodies

Basics of Archimedes’ Principle: Explaining Buoyancy

Remember that the Archimedes’ Principle explains buoyancy or more specifically, the upward force exerted by a fluid called buoyant force. The principle states that the buoyant force acting on a submerged object is equal to the weight of the liquid displaced by the object.

It can be summed up as follows: An object sinks if the weight of the water it displaces is less than the weight of that particular object. On the other hand, that object will neither sink nor rise if its weight is equal to the weight of the water it displaces.

Ships are notable examples. When launched into a body of water, a specific ship would naturally sink until the weight of the water it displaces becomes equal to its own weight. However, as the ship is loaded, it sinks further and displaces more water. The magnitude of the buoyant force continuously matches the weight of the ship.

Take note that the principle also explains that an object will rise if its weight is less that of the displaced fluid. Examples of this phenomenon include paper boats, a block of wood, and plastics placed on a body of water.

Shortcomings: Limitations of the Archimedes’ Principle

One of the major problems or limitations of the Archimedes’ Principle is that it does not take into consideration other factors that can affect the dynamics between an object and fluid. Consider surface tension as an example.

Surface tension refers to the tendency of fluid surfaces to shrink into the minimum surface area possible. It is essentially an attractive force exerted upon by liquid molecules on the surface by other liquid molecules beneath. The phenomenon allows certain insects to float and slide on a water surface.

The principle also breaks down in certain conditions, especially in complex fluids. These complexities are present in both natural and deliberate settings. For example, in industrial applications, heavy salts or colloidal nanoparticles are added to fluids to create a density gradient in the solvent needed to separate the various components in suspension.


  • Mohazzab, P. 2017. “Archimedes’ Principle Revisited.” Journal of Applied Mathematics and Physics. 5(4): 836-843. DOI: 10.4236/jamp.2017.54073
  • Wilson, R. M. 2019. “Archimedes’ Principle Gets Updates.” Physics Today. 65(9): 15-17. DOI: 10.1063/PT.3.1701
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