Tuesday, 13 February 2018

DEFINE BUOYANCY AND BUOYANCY FORCE

DEFINE BUOYANCY AND BUOYANCY FORCE

We were discussing the basic definition and derivation of total pressurecentre 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.

 

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.

 

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.

 
We will see another topic i.e. Centre of buoyancy in our next post.

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

Reference:

Strength of material, By R. K. Bansal
Image Courtesy: Google

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