BlogIIT-JEEImportant Topic of Physics: Buoyancy

Important Topic of Physics: Buoyancy

While underwater, we may see that lifting our entire body’s weight is simple. This is due to a phenomenon known as buoyant force, which we may encounter in the sea. It is a fluid’s upward force. When it comes to pressure in a fluid, buoyancy is a simple notion to grasp. Pressure rises with depth in a fluid, whether it’s a gas or a liquid. The buoyant force offers an object in a fluid its upward lift, but it’s also equivalent to the mass of the fluid it’s displaced. Archimedes discovered this in the third century B.C. This is known as Archimedes’ Principle.

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    A brief outline

    We have a full glass of water in front of us. It’s so full that putting anything else in it will cause the water to spill over the edge. If we collect the water that flows out, we will discover that it has the same volume as the object we placed in the glass. This is what we mean when we say “displace the fluid,” and it’s also a quick way to figure out how big an irregularly shaped object is. As a result, we can state that the buoyant force is equal to the weight of the displaced fluid, not the object’s weight.

    If the weight of the submerged object equals the buoyant force (the weight of the displaced fluid), the object will neither sink nor float. If the thing’s weight is greater than the buoyant force, the object will sink. If the object’s weight is low enough, it will rise to the surface and float. As a result, buoyancy is the Archimedes phenomenon, which states that when an item is entirely or partially immersed in a liquid, it experiences an upward force.

    Important Concepts

    Cause of Buoyancy

    When an object is submerged in water or any other fluid, we notice that the object is subjected to a downward force opposing gravitational attraction, which causes the object’s weight to drop. The weight of an object submerged in a liquid is counteracted by the upward force exerted by the fluid. The pressure in a fluid column increases with depth, as we all know. As an outcome, the pressure at the bottom of a submerged surface is greater than at the top. The difference in pressure causes the material to undergo a net upward force, which we name buoyancy.

    Object float or sink in water

    1. A single column of liquid can be thought of as a concoction of multiple overlapping layers, one on top of the other, with changing pressure.
    2. Because the number of layers of the liquid that are overlying, i.e., the layers one over the other, increases as we go down in the liquid, the pressure at the bottom would be larger than at the top.
    3. Because of the pressure differences between both the layers, a made-up force is imparted to it in the up direction. The object which has been immersed accelerates upward due to this force. The force has always been directed vertically.
    4. The magnitude of the upward force is also equivalent to the difference in pressure between the topmost and last layers, as well as the weight of the fluid expelled.
    5. Floating is the result of the preceding notion. The object must be less dense than water; otherwise, it will sink if its density is higher.

    Buoyant Force formula

    Buoyant force in terms of pressure is given as:

    Fb = PA

    Fb = Buoyant force

    P = Pressure

    A = Area

    Using area, height and volume, the formula becomes,

    Fb= ρ * g * h *A

    Fb = Buoyant force

    ρ = Density of liquid

    g = Gravity

    h = Height of the submerged part

    A = Area

    The buoyant force can be used in a variety of ways. The following are some of the applications: Submarine: The submarine’s enormous ballast tank is very useful for controlling its position and depth. As the submarine submerges in water, the ballast tank allows water to enter the submarine, causing it to weigh more than the buoyant force.

    Balloons in the air

    The hot air balloon is raised and floats thanks to the buoyant force. The buoyant force of the atmosphere acts on the object. When the weight of the hot air balloon exceeds the buoyant force, the balloon drops. When the buoyant force and the weight of the hot air balloon are equal, it becomes stable.

    Types of buoyancy

    • Positive buoyancy, negative buoyancy, and neutral buoyancy are the three main types of buoyancy.
    • The thing floats due to positive buoyancy, which occurs when the immersed object is lighter than the fluid displaced.
    • Negative buoyancy occurs when the buried object is heavier than the displaced fluid, forcing the object to sink.
    • When the mass of an immersed item balances the fluid displaced, neutral buoyancy happens. The scuba diver took a dive.

    Significance of buoyancy in IIT JEE exam

    This unit is where the majority of theoretical questions are asked. Concentrate your efforts on gaining a better knowledge of buoyancy and its force. Because formula-based questions are common in this section, memorize all of the formulas and utilize them appropriately when answering the questions. The physics subject of JEE 2019 was rated as the most difficult of the three divisions. The questions were difficult and time-consuming, and pupils had to put in extra effort to answer them. There were 13 questions on electromagnetic, 8 questions on mechanics, 2 questions on modern physics, 3 questions on optics, 3 questions on thermodynamics, 1 question on SHM, and 1 question on waves.


    What role does buoyant force play in swimming?

    In swimming, buoyancy is crucial because it allows the swimmer to stay closer to the surface. This is due to the fact that the pressure felt by the swimmer beneath the water is greater than the pressure felt above. This is also why swimmers are able to float on the water's surface.

    What is the source of buoyancy?

    The buoyancy is caused by the pressure produced by the fluid in which the object is submerged. Furthermore, because the pressure of the fluid increases with depth, the buoyant force experienced by the object is constantly upwards.

    What is the relationship between buoyancy and density?

    The buoyant force, also known as buoyancy, is proportional to the density of the submerged fluid.

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