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Difference between Buoyancy and Upthrust

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  • Last Updated : 30 Jun, 2022

In fundamental physics, the terms buoyancy and upthrust are sometimes used frequently. Even though some of us use them similarly, in spite of knowing they have different meanings. Buoyancy is an object’s ability to float in a fluid, whereas upthrust is a force imposed on an object by the fluid in which it is submerged. Simply said, buoyancy is the tendency of an object to rise when submerged in a certain fluid. However, upthrust is the buoyant force exerted by the fluid on the object. This is the main difference between buoyancy and upthrust.

Buoyancy-vs-Upthrust

What is Buoyancy?

Buoyancy is defined as the ability of an object to float in a fluid or liquid. The ability of an object depends on the density of the fluid and the properties of the object like size, shape, and density of the object.

However, the ability of buoyancy, or an object’s capability to float, is determined by the density of the fluid as well as the properties of the object (density of the object, shape of the object, etc.). The buoyancy effect of a fluid increases with its density. 

The buoyancy effect of an object increases with its weight. Simply put, the buoyancy power is determined by the density differential between the fluid and the item. The effective density of an object, on the other hand, can be modified in a variety of ways. A hollow cylinder, for example, has a lower effective density than a solid cylinder constructed of the same material.

The buoyancy effect has hundreds of uses, including hydrometers, ships, and submarines. The buoyancy effect can also be used to calculate solid and liquid density.

What is Upthrust? 

Upthrust is defined as the force that is exerted on an object by the fluid when the object is submerged. It is also called as buoyant force. It always acts upwards. It always acts against the weight of an object.

Upthrust is essential in various applications, particularly marine engineering and cargo transport. Ships and boats are built in such a way that the weight of water displaced by the vessel equals the weight of the vessel when partially immersed in the sea. 

As a result, they float in the sea using Archimedes’ principle. With increasing load weight, the volume of the underwater component of the hull steadily increases. To avoid overloading, it is critical to check the power of the upthrust (vessel stability) when loading. 

Normally, the hull of a vessel is marked with load lines (also known as Plimsoll lines), which aid in monitoring the vessel’s stability.

Difference between Buoyancy and Upthrust

Buoyancy

Upthrust

Buoyancy is defined as the ability of an object to float in a fluid or liquid. Upthrust is defined as the force that is exerted on an object by the fluid when the object is submerged.
It is the ability of a fluid or an object. It is the force.
In buoyancy, the main factor is the density of the fluid. In upthrust, the main factor is the weight of the object.
It is the phenomenon that is caused by the buoyant force It is also called buoyant force.

Some applications of buoyancy. that they are 

  • Used in hydrometers.
  • Used is submarines.
  • Used to determine the density of the liquids and solids.

Some applications of upthrust are 

  • It is used in marine engineering.
  • It is used in cargo transport.
  • Used in boats and ships. 
It does not act against the weight of an  object  It always acts against the weight of the object.
It does not act upwards. It acts always upwards.

Sample Questions

Question 1: What does Archimedes’ principle state about upthrust?

Answer: 

Archimedes principle is used to determine the magnitude of the upthrust. It is a law of fundamental physics to fluid mechanics. It states that the buoyant force that is exerted on a body when immersed in the fluid is equal to the weight of the fluid that is

Question 2: What is the formula of buoyant force according to Archimedes’ principle?

Answer:

Buoyant force is defined as the force that is exerted on an object by the fluid when the object is submerged. It is also called as upthrust. It always acts upwards. It always acts against the weight of an object.

Formula: 

Fb = ρ × g × V 

where, 

  • Fb = Buoyant force.
  • ρ = density of fluid.
  • g = acceleration due to gravity.
  • V = volume of the fluid.

Question 3: Find the buoyant force, if a ball of a radius of 40 cm is immersed in water.

Answer:

Given radius of the ball r = 40cm = 0.4m.

Therefore, volume of ball V = (4/3)πr3.

V = (4/3)×3.14×(0.4)3

V =2.68 m3.

ρ = density of water = 1000kg/m3.

g = acceleration due to gravity = 9.8 m/s2.

From Archimedes principle, buoyant force formula,

Fb = ρgV 

Fb = 1000 × 9.8 × 2.68

Fb = 26,264 N.

Therefore, the buoyant force is 26264 N.

Question 4: Where is Archimedes’ principle used?

Answer:

It is used in the design principle of hydrometers, submarines and ships. Archimedes principle is used to determine the magnitude of the upthrust. 

Question 5: What are the units of buoyant force and define them? 

Answer:

Buoyant force is defined as the force that is exerted on an object by the fluid when the object is submerged. It is also called as upthrust. It always acts upwards. It always acts against the weight of an object.

Units:

 S.I units of buoyant force iNewton 

Question 6: What are the types of buoyancy?

Answer:

Buoyancy is defined as the ability of an object to float in a fluid or liquid.

There are three types of buoyancy, they are 

  • Positive buoyancy: When the object immersed is lighter than the fluid displaced it is positive buoyancy. In this the object floats on the fluid.
  • Negative buoyancy: When the object immersed is denser than the fluid displaced it is negative buoyancy. In this the object sinks in the fluid. 
  • Neutral buoyancy: When the weight of immersed object is equal to the fluid displaced it is neutral buoyancy.
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