Archimedes' principle.
Archimedes' principle is named after Archimedes of Syracuse, who first discovered this law. His
treatise, On floating bodies, proposition 3 states, that:
* Any floating object displaces its own weight of fluid.
For more general objects, floating and sunken, and in gases as well as liquids (i.e. a fluid), Archimedes'
principle may be stated thus in terms of forces:
*Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the
fluid displaced by the object.
With the clarifications that for a sunken object the volume of displaced fluid is the volume of the object,
and for a floating object on a liquid, the weight of the displaced liquid is the weight of the object.
More tersely:
Buoyancy = weight of displaced fluid.
Archimedes' principle does not consider the surface tension (capillarity) acting on the body.
*The weight of the displaced fluid is directly proportional to the volume of the displaced fluid (if the
surrounding fluid is of uniform density). In simple terms, the principle states that the buoyant force on
an object is going to be equal to the weight of the fluid displaced by the object, or the density of the
fluid multiplied by the submerged volume.
Thus, among completely submerged objects with equal
masses, objects with greater volume have greater buoyancy.
Suppose a rock's weight is
measured as 10 Newtons when
suspended by a string in a
vacuum with gravity acting
upon it. Suppose that when the
rock is lowered into water, it
displaces water of weight
6 Newtons. The force it then
exerts on the string from which
it hangs would be 10 Newtons
minus the 6 Newtons of
buoyant force:
10 − 6 = 4 Newtons. Buoyancy
reduces the apparent weight of
objects that have sunk completely to the sea floor.
It is generally easier to lift an object up through the water than it is to pull it out of the water.
Assuming Archimedes' principle to be reformulated as follows:
The buoyant force on a submerged object is equal to the weight of the fluid displace.
FA = ρ* g*V
The buoyant force on a submerged object is equal to the weight of the liquid displaced by the object. For
water, with a density of one gram per cubic centimeter, this provides a convenient way to determine the
volume of an irregularly shaped object and then to determine its density.
The buoyant force on a submerged object is equal to the weight of the liquid displaced by the object. For
water, with a density of one gram per cubic centimeter, this provides a convenient way to determine the
volume of an irregularly shaped object and then to determine its density.
Example: If you drop wood into water buoyancy will keep it afloat.
http://en.wikipedia.org/wiki/Archimedes
http://en.wikipedia.org/wiki/Buoyancy