Editing Archimedes' principle (section)

==Principle of flotation==
Archimedes' principle shows the  buoyant force and displacement of fluid. However, the concept of Archimedes' principle can be applied when considering why objects float. Proposition 5 of Archimedes' treatise ''[[On Floating Bodies]]'' states that
{{Quotation|Any floating object displaces its own weight of fluid.| [[Archimedes]] of [[Syracuse, Sicily|Syracuse]]<ref name=archimedes>{{cite web|url=https://archive.org/stream/worksofarchimede00arch#page/256/mode/2up|title=The works of Archimedes|page=257|access-date=11 March 2010|quote=Any solid lighter than a fluid will, if placed in the fluid, be so far immersed that the weight of the solid will be equal to the weight of the fluid displaced. |publisher=Cambridge, University Press|year=1897}}</ref>}}

In other words, for an object floating on a liquid surface (like a boat) or floating submerged in a fluid (like a [[submarine]] in water or [[dirigible]] in air) the weight of the displaced fluid equals the weight of the object. Thus, only in the special case of floating does the buoyant force acting on an object equal the objects weight. Consider a 1-ton block of solid iron. As iron is nearly eight times as dense as water, it displaces only 1/8 ton of water when submerged, which is not enough to keep it afloat. Suppose the same iron block is reshaped into a bowl. It still weighs 1 ton, but when it is put in water, it displaces a greater volume of water than when it was a block. The deeper the iron bowl is immersed, the more water it displaces, and the greater the buoyant force acting on it. When the buoyant force equals 1 ton, it will sink no farther.

When any boat displaces a weight of water equal to its own weight, it floats. This is often called the "principle of flotation": A floating object displaces a weight of fluid equal to its own weight. Every ship, submarine, and dirigible must be designed to displace a weight of fluid at least equal to its own weight. A 10,000-ton ship's hull must be built wide enough, long enough and deep enough to displace 10,000 tons of water and still have some hull above the water to prevent it from sinking. It needs extra hull to fight waves that would otherwise fill it and, by increasing its mass, cause it to submerge. The same is true for vessels in air: a dirigible that weighs 100 tons needs to displace 100 tons of air. If it displaces more, it rises; if it displaces less, it falls. If the dirigible displaces exactly its weight, it hovers at a constant altitude.

While they are related to it, the principle of flotation and the concept that a submerged object displaces a volume of fluid equal to its own volume are ''not'' Archimedes' principle. Archimedes' principle, as stated above, equates the ''buoyant force'' to the weight of the fluid displaced.

One common point of confusion{{by whom|date=May 2018}} regarding Archimedes' principle is the meaning of displaced volume. Common demonstrations involve measuring the rise in water level when an object floats on the surface in order to calculate the displaced water. This measurement approach fails with a buoyant submerged object because the rise in the water level is directly related to the volume of the object and not the mass (except if the effective density of the object equals exactly the fluid density).<ref>{{cite book |last1=Mohindroo |first1=K. K. |title=Basic Principles of Physics |date=1997 |publisher=Pitambar Publishing |isbn=978-81-209-0199-5 |pages=76–77 |url=https://books.google.com/books?id=xsffXbNqpOsC&q=a+buoyant+submerged+object+because+the+rise+in+the+water+level+is+directly+related+to+the+volume+of+the+object+and+not+the+mass&pg=RA7-PA77 |language=en}}</ref><ref>{{cite book |last1=Redish |first1=Edward F. |last2=Vicentini |first2=Matilde |last3=fisica |first3=Società italiana di |title=Research on Physics Education |date=2004 |publisher=IOS Press |isbn=978-1-58603-425-2 |page=358 |url=https://books.google.com/books?id=tv59xh7lmykC&q=a+buoyant+submerged+object+because+the+rise+in+the+water+level+is+directly+related+to+the+volume+of+the+object+and+not+the+mass&pg=PA358 |language=en}}</ref><ref>[http://www.carpeastra.co.uk/showpage.php?pageName=04_proof  Proof of Concept] carpeastra.co.uk</ref>