Archimedes’ Buoyancy Principle

22.03.2015 |

Episode #4 of the course “Scientific laws and theories everyone should know”

After discovering the principle of buoyancy, ancient Greek scholar Archimedes supposedly said, “Eureka!” and ran through the city of Siracusa, Italy without any clothing. But he may have had a reason to be naked. As the story is told, Archimedes happened upon this amazing discovery after noticing how the water rose when he got into his bathtub.

Floatation as a science is very fascinating. While you may know that every object has a particular volume and that volume has a weight, do you also understand why that object will cause the level of water to rise if placed in the water? This is what Archimedes discovered. The water will move only equal to the volume of the object that was placed in the water. This principle applies to all fluids, whether the liquid is water or something else.

The volume of water that rises and is displaced carries a certain mass, which is explained by this formula: mass of water displaced = volume of water displaced * density of water.

Freshwater usually has a density of 1000 kg/m3 and changes a bit depending on whether the water contains certain levels of salt, among other factors. Archimedes demonstrated that in reality, the mass or amount of water displaced pushes the object upward. This push seems to result in a loss of weight by the same amount of water that was originally displaced.

The exerted force that pushes upward by the volume of water that is displaced is referred to as the power of buoyancy. Most experts accept that this force acts at a specific location on the body, which is referred to as the body’s center of buoyancy. The center of buoyancy always equally relates to the center of gravity of the body part that is under the water. Due to the force of buoyancy, the object is kept afloat, or pushed up, and is in this way prevented from sinking.


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