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How to Calculate Buoyant Force


Welcome to this comprehensive guide on how to calculate buoyant force. Whether you are a physics student, an engineer, or simply curious about the principles of buoyancy, this article will provide you with a detailed understanding of how to determine the buoyant force acting on an object submerged in a fluid.

We will look into the underlying concepts, equations, and practical applications of buoyancy calculations. So, let us begin!

How to Calculate Buoyant Force: Explained

Understanding Buoyancy

Before we go into the specifics of calculating buoyant force, let us first understand what buoyancy is.

Definition of Buoyancy: Buoyancy is the upward force exerted by a fluid on an object immersed in it. This force opposes the weight of the object and enables it to float or be suspended in the fluid. Archimedes’ principle, formulated by the ancient Greek mathematician Archimedes, states that the buoyant force acting on an object is equal to the weight of the fluid displaced by that object.

How to Calculate Buoyant Force
How to Calculate Buoyant Force

The Equation for Buoyant Force

The equation for calculating buoyant force is relatively straightforward. It can be expressed as follows:

Buoyant Force (Fb) = ρ × V × g


  • Fb represents the buoyant force in Newtons (N).
  • ρ denotes the density of the fluid in kilograms per cubic meter (kg/m³).
  • V is the volume of the fluid displaced by the object in cubic meters (m³).
  • g represents the acceleration due to gravity, approximately 9.8 m/s².

Step-by-Step Calculation Process

To calculate the buoyant force exerted on an object, follow these steps:

  1. Determine the density of the fluid in which the object is immersed. This information can usually be found in reference materials or obtained through experimentation.
  2. Measure or calculate the volume of the fluid displaced by the object. This can be determined by various methods, such as measuring the change in fluid level or using geometric formulas for regular-shaped objects.
  3. Multiply the density of the fluid by the volume displaced and the acceleration due to gravity to obtain the buoyant force.

Example Calculation: Buoyant Force of a Submerged Object

Let us solve a problem to illustrate the process of determining the buoyant force. Suppose we have a solid iron sphere with a density of 7,800 kg/m³ submerged in water.

Step 1: Density of Water
The density of water is approximately 1,000 kg/m³.

Step 2: Volume Displaced
For a sphere, you can calculate the volume by using the formula: V = (4/3) × π × r³.
Let’s assume the radius of the sphere is 0.5 meters. Plugging this value into the formula, we find: V = (4/3) × 3.14 × (0.5)³ = 0.524 m³.

Step 3: Calculation
Now, we can calculate the buoyant force using the formula: Fb = ρ × V × g.
Substituting the values, we get: Fb = 1,000 kg/m³ × 0.523 m³ × 9.8 m/s² = 5,131.93 N.

Therefore, the buoyant force exerted on the iron sphere submerged in water is approximately 5132 Newtons.

Frequently Asked Questions (FAQs)

  1. What is the formula for calculating density?
  • A: We calculate Density by dividing the mass of an object by its volume. The formula is Density (ρ) = Mass (m) / Volume (V).

2. Can the buoyant force ever be greater than the weight of the submerged object?

  • A: No, the buoyant force can never exceed the weight of the object. If it did, the object would accelerate upwards and eventually escape the fluid.

3. Are there any real-world applications of buoyancy calculations?

  • A: Absolutely! Buoyancy calculations are essential in various fields, including shipbuilding, aerospace engineering, and even everyday activities like swimming and hot air ballooning.

4. Does the shape of the object affect the buoyant force?

  • A: Yes, the shape of an object plays a role in determining the buoyant force. Objects with larger volumes displace more fluid, resulting in a greater buoyant force.

5. Can you provide an example where buoyancy is not applicable?

  • A: Buoyancy is not applicable in a vacuum or when dealing with gases, as they do not exert a buoyant force on objects.

6. How does the buoyant force change with the depth of immersion?

  • A: The buoyant force remains constant regardless of the depth of immersion, as long as the volume of fluid displaced remains the same.


In conclusion, understanding how to calculate buoyant force is crucial for comprehending the principles of buoyancy. By following the simple equation and step-by-step process outlined in this article, you can determine the upward force exerted on an object submerged in a fluid.

Whether you are learning the physics of floating objects or applying buoyancy calculations to practical engineering problems, this knowledge will prove invaluable. So go ahead, apply your newfound expertise, and unlock the mysteries of buoyancy!

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