Table of Contents
Introduction:
Why our body feels lighter in a swimming pool? Why does an object’s weight decrease in the water? How can heavy ships float in the water while a needle sinks in it? All these questions can be answered through Archimedes’ Principle.
To understand Archimedes’ Principle, we are going to take an example of object A. Let’s say this object A has X kg of weight in air and V cubic meter of volume. Now take a bucket of water and fully submerged object A in it. After that take a spring weight machine and measure the weight of object A while it is fully submerged. Now note down the weight. Let’s say we got Y kg. Now if you compare both the weight you will find that the submerged weight is less than the air weight. That means Y kg is less than X kg in this case. So now a question arises. Why suddenly did the weight of object A get reduced when it submerged into the water?
That’s what Archimedes’ Principal explains. According to Archimedes’ Principal weight of the object, A got reduced due to the upward force applied by the water in which it got submerged. This upward force is called Buoyancy Force and the magnitude of the buoyancy force which reduces the weight of the object exactly equals the weight of the water displaced by it.
In our example object, A has V cubic meter volume. Since it is fully submerged so it will displace V cubic meter of water in the bucket and the buoyancy force will be equal to the weight of this V cubic meter volume of displaced water.
So, whenever we enter the swimming pool our body displaces some water, and because of its water applies buoyancy force on our body and that’s we feel lighter in the pool. The same thing happens in the case of any object when it is partially or fully submerged in any fluids. Its weight got reduced due to the buoyancy force.
The big heavy ships do not sink in water because they displace the amount of water which have more weight than the ship itself while the needle is not able to displace enough amount of water that’s why it sinks.
Archimedes’ Principal:
So, from all the discussed examples, we can summarize Archimedes’ Principal as –
Whenever a body is partially or fully submerged in the fluid then fluid exerts an upward force which is called Buoyancy force on the submerged body. The magnitude of the buoyancy force which fluid exerts on the submerged body equals the weight of the fluid displaced by the body.
Note – The deeper we go in a liquid the more pressure we feel but buoyancy force does not depend on the depth of the fluid it only depends on the weight of the liquid displaced.
Archimedes’ Principal Formula:
Fb = ρ× g× V
Fb = Upward force or buoyancy force applied by the liquid on the submerged body.
ρ = Density of the fluid.
V = The amount of volume which has been submerged into the fluid.
g = Acceleration due to gravity.
Apparent Weight = Weight of an object in the air – Magnitude of Buoyancy force
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