Buoyancy is the upward force exerted by a fluid on an object submerged or partially submerged in it. The buoyant force depends on the volume of fluid displaced by the object and the density of the fluid. Objects with densities lower than the fluid they displace will float due to positive buoyancy, while objects with higher densities will sink due to negative buoyancy. The location of an object's center of buoyancy relative to its center of gravity determines its stability in a fluid.

2. Buoyancy is the ability of an object to float when
submerged in a fluid. Any object completely or partially
submerged in a fluid will experience an upward buoyant
force that is equal to the weight of the fluid that is
displaced.

4. Buoyant force can be defined as an upward force
exerted on an object that is completely or partially
submerged in liquid. The unit of the buoyant force is
Newton. Buoyancy force depends upon two factors:
• Amount (Volume) of liquid displaced by the object
• The density of the object.

5. • In the first example, the iron nail has less volume and
displaces a very less amount of water, so there is less
buoyant force (upward force), and therefore sinks.
Whereas ships have more volume, displace more
water, and therefore have greater buoyant force
(upward force) by water, and it floats. When talking in
terms of relative density, if the relative density is less
than 1, the object floats in water, and if the relative
density is more than 1, the object sinks.

6. • Positive buoyancy: When the weight of an object is
lighter than the fluid it displaces is called positive
buoyancy. For example, a boat that weighs (3000 kg)
but displaces (4500 kg) of water will easily float
• Negative buoyancy: When the weight of an object is
greater than the fluid it displaces is called negative
buoyancy. For example, an iron nail may weigh 27
grams, but if it only displaces 17 grams of water, it will
sink.
• Natural buoyancy: When the weight of an object is
equal to the fluid it displaces. For example, a
submarine can adjust its weight by adding or
expelling water in special tanks called ballast tanks is
an example of natural buoyancy.

7. How much of an object's surface touches
the water has an effect on its buoyancy. A
very large ship has a lot of surface area,
which means that the ship's weight is
spread out over a lot of water, all of which
is pushing up on the ship. If the same ship
was in the water with the bow pointing
down, it would start to sink because all of
the weight is concentrated in one small
area, and the water it is displacing weighs
less than the weight of the ship.

8. A common example used to demonstrate
this is a person floating in water. If the
person floats on her back, her entire body
can stay at or near the water's surface.
When she floats in the water with her feet
down, she'll sink farther; typically, only her
upper body will stay at the top of the
water.

9. Stability in a fluid depends on the location
of an object's center of buoyancy in
relation to its center of gravity. An object's
center of gravity is the point in the object
where all of the object's weight appears to
be concentrated; it can also be thought of
as the average location of the object's
weight. The center of buoyancy is the
center of gravity of the water that the
object has displaced. This is not in the
water, but in the object floating on it.

11. Reserve buoyancy is the volume of
the enclosed spaces above the
waterline. Reserve buoyancy is a
very important factor in determining
a ship’s seaworthiness minimum
freeboards are assigned to a ship to
ensure that there is adequate
reserve buoyancy at all times.

13. A ship’s waterline is the line
where its hull meets the surface
of the water. A load line, also
called Plimsoll mark,1 is a
marking indicating the extent to
which the weight of a load may
safely submerge a ship, by way
of a waterline limit.

14. The purpose of the load line is to ensure
that a ship has sufficient freeboard (the
height from the waterline to the main deck)
and thus sufficient reserve buoyancy
(volume of ship above the waterline). It
should also ensure adequate stability and
avoid excessive stress on the ship’s hull as
a result of overloading. Ships intended for
the carriage of timber deck cargo are
assigned a smaller freeboard as the deck
cargo provides protection against the
impact of waves.