The force due to the gravitational attraction of the earth acts on the bottle in a downward direction. So the bottle is pulled downwards. But the water exerts an upward force on the bottle. Thus, the bottle is pushed upwards. We have learnt that the weight of an object is the force due to the gravitational attraction of the earth. When the bottle is immersed, the upward force exerted by the water on the bottle is greater than its weight.
Therefore it rises up when released.
To keep the bottle completely immersed, the upward force on the bottle due to water must be balanced. This can be achieved by an externally applied force acting downwards.
This force must at least be equal to the difference between the upward force and the weight of the bottle.
The upward force exerted by the water on the bottle is known as upthrust or buoyant force. In fact, all objects experience a force of buoyancy when they are immersed in a fluid.
The magnitude of this buoyant force depends on the density of the fluid.

Table of Contents

What is Buoyant Force?

What causes Buoyant Force?

Demonstration of Buoyant Force

Why does an object float or sink in water?

Applications of Buoyant Force

Frequently Asked Questions – FAQs

What is Buoyant Force ?

The upward force applied to an object that is fully or partially submerged in a fluid is known as the buoyant force. Upthrust is another name for this upward thrust. A body submerged partially or completely in a fluid appears to lose weight, or to be lighter, due to the buoyant force.

Following factors affect buoyant force:
i) the density of the fluid
ii) the volume of the fluid displaced
iii) the local acceleration due to gravity

A substance that has a density greater than the liquid it is submerged in has a tendency to sink. The force can keep an object afloat if it is either less dense than the liquid or is shaped properly (like a boat).it floats in water and substances with a relative density greater than one sink in water.

What causes Buoyant Force ?

When an object is submerged in water or any other liquid, we notice that it experiences a force opposite the gravitational pull from the downward direction, which results in a loss of weight. The fluid’s upward force works against the weight of an object submerged in the fluid. As we are all aware, a fluid column’s pressure rises with depth. As a result, an object submerged in fluid experiences greater pressure at its bottom than its top. Because of this pressure difference, the object experiences a net upward force that we refer to as buoyancy.

Demonstration of Buoyant Force

When we immerse an object in a fluid, the object feels an upward force. This force, which we refer to as the buoyant force, is applied to the object by the fluid and causes it to rise. This force’s strength is exactly equal to the weight of the liquid that is being displaced.

The Center of Buoyancy is the location of the buoyant force or the location on the object where the force acts.

Why does an object float or sink in water?

The nail sinks. The force due to the gravitational attraction of the earth on the iron nail pulls it downwards. There is an
upthrust of water on the nail, which pushes it upwards. But the downward force acting on the nail is greater than the upthrust of water on the nail. So it sinks

The cork floats while the nail sinks. This happens because of the difference in their densities. The density of a substance is defined as the mass per unit volume. The density of cork is less than the density of water. This means that the upthrust of water on the cork is greater than the weight of the cork. So it floats.

The density of an iron nail is more than the density of water. This means that the upthrust of water on the iron nail is less than the weight of the nail. So it sinks.

Therefore objects of density less than that of a liquid float on the liquid. The objects of density greater than that of a liquid sink in the liquid.

Applications of Buoyant Force

Human swimmers, fish, ships, and icebergs all float because of buoyancy. Below are some examples of buoyancy applications.

Swimmers, fish, ships, and icebergs can all float thanks to buoyancy. Some of the prominent applications of buoyancy are given below:

Hot Air Balloon
Any object will be buoyed by the air that makes up the atmosphere. The buoyant force causes a hot air balloon to rise and float. When the weight of the balloon exceeds the buoyant force, it descends. When the weight and buoyant force are equal, the object becomes stationary.

A ship can displace enough water to have a weight equal to the ship’s weight, which allows the ship to float on the water’s surface. A hollow shape is used in the construction of ships to reduce their overall density below that of seawater. The buoyant force exerted on the ship is therefore sufficient to bear its weight.

A particular species of fish uses the Archimedes principle to ascend and descend the water. The fish will fill the air sacs in its swim bladder with gas in order to rise to the surface. Their body becomes lighter as a result of the gases diffusing from their own body to the bladder. The fish can now rise as a result.

Frequently Asked Questions – FAQs

Q . What are the benefits of buoyant force in swimming?
Ans – Swimming requires buoyancy because it allows the swimmer to stay near the surface. This is so because the pressure beneath the water is greater than the pressure above it for the swimmer. Swimmers can float on the water’s surface for the same reason.

Q . Why is buoyancy caused ?
Ans -The buoyancy of an object is caused by the pressure that the fluid exerts on it while it is submerged. Because the fluid’s pressure rises with depth, the buoyant force that an object experiences is also always upward.

Q. What three types of buoyancy are there?
Ans – Positive buoyancy, negative buoyancy, and neutral buoyancy are the three different types of buoyancy.

The object floats because of positive buoyancy, which occurs when the immersed object is lighter than the fluid displaced.

When an object is submerged and its density is greater than the fluid being displaced, the object sinks due to negative buoyancy.

When the weight of an immersed object is equal to the volume of fluid displaced, neutral buoyancy occurs. The scuba diver’s dive is the perfect illustration of neutral buoyancy.

Q . What are a few buoyancy examples?
Ans – Examples of buoyancy include a ship or boat floating in the water and a cork floating there.

Q. How are density and buoyancy related?
Ans – The buoyant force, also known as buoyancy, is inversely proportional to the fluid’s density.

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