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THERMO Spoken Here! ~ J. Pohl © ~ 2019 | www.ThermoSpokenHere.com (B3680-097) |

A solid in equilibrium on Earth rests upon solid Earth or is supported in some floating freely partially or fully submerged in a fluid, perhaps assisted in equilibrium by an external tether or such which, in turn, rests or anchors to solid Earth. There are a number of possibile arrangements.

Stable solid/fluid configurations depend upon the mass of the solid and fluid densities. Here we consider the case of a solid floating beneath air and above water.

Shown right is sketch of a mass of arbitrary shape. The mass "floats" as we say. The part that floats (notated "**f**") is above the water level surrounded by air. The part of the mass surrounded by water is notated "**s**" for submerged. A vertical projection of the mass (its area seen from the "vertical") is needed: "**A**." What does Newtion's 2nd Law tell us?

The final equation above indicates that the required tension, **T** is diminished by the presence of both the air and the water and this is in proportion to the "displaced " air or water, respectively. Next we do a tad more algebra to obtain as below:

The third, right-most term of the equation above is called the "buoyant force." Notice this is the mass of water displaced. The volume of which is the volume "submerged."