We
were discussing the basic definition and derivation of total
pressure; centre
of pressure and we have also secured the expression for total
pressure and centre of pressure for inclined plane surface submerged in liquid in
our previous posts.

Today
we will start a new topic i.e. Buoyancy and floatation, in the subject of fluid
mechanics, with the help of this post. We will see here the basic concept of
Buoyancy, Archimedes principle, Centre of buoyancy, Metacentre, Metacentric
height etc.

We
will first see here the basic concept of buoyancy or buoyancy force with the
help of this post.

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Buoyancy or buoyancy force

When
a body is immersed in fluid, an upward force is exerted by the fluid on the
body. This force will be equal to the weight of the fluid displaced by the body
and this force will be termed as force of buoyancy or buoyancy.

Let
us consider we have one container filled with water as displayed here in
following figure. We have one object of weight 7 N. Let us think that we are
now immersing the object in to the liquid i.e. water.

Once
object will be immersed in the water, some amount of water will be displaced by
the object and one upward force will be applied over the object by the water.

Weight
of the displaced water will be equal to this upward force which will be exerted
by the water on the object. As we can see from above figure that, water of
weight 3N is displaced here and one upward force of 3N is exerted by the water
over the object.

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Conclusion for buoyancy
force

Buoyancy
force is the force which will be exerted on the object by the surrounding fluid.
When one object will be immersed in the water, object will push the water and
water will push back the object with as much force as it can.

Force
of buoyancy = Weight of the displaced fluid

Force
of buoyancy = Weight of the object in air – Weight of the object in given water

####
**Positive buoyancy**

Force
of buoyancy will be greater than the weight of the object. Hence, object will
float and this case will be termed as positive buoyancy.

####
**Neutral buoyancy**

Force
of buoyancy will be equal to the weight of the object. Hence, object will be
suspended in the fluid and this case will be termed as neutral buoyancy.

####
**Negative buoyancy**

Force
of buoyancy will be less than the weight of the object. Hence, object will be
sunk and this case will be termed as negative buoyancy.

Do
you have any suggestions? Please write in comment box.

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**Reference:**

Strength
of material, By R. K. Bansal

Image
Courtesy: Google