Buoyancy. Archimedes’ Principle and density
The online buoyancy simulations on this page will help you understand the physical fundamentals that make some objects float and others not. We will discover Archimedes’ Principle and we will see what is the relationship between buoyancy and density.
This Thematic Unit is part of our Physics collection

STEM OnLine mini dictionary
Apparent Weight
Net force acting on a submerged body, resulting from the difference between its real weight and the buoyant force (Pa = P – E) in the SI.
Archimedes’ Principle
Law stating that any body immersed in a fluid experiences an upward buoyant force equal to the weight of the displaced fluid.
Buoyant Force
Upward vertical force exerted by a fluid on a submerged body, calculated as E = ρ * V * g in the SI (in Newtons).
Center of Buoyancy
Point where the buoyant force is considered to be applied, coinciding with the center of gravity of the displaced fluid volume.
Density
Scalar quantity expressing the amount of mass per unit volume of a substance, measured in kg/m³ in the SI.
Displaced Volume
Space occupied by the fluid that has been moved aside by the body upon immersion, measured in m³ in the SI.
What is buoyancy
Buoyancy is the ability of bodies to stay on the surface of a liquid or in the air without sinking. It is a fundamental physical principle governed by Archimedes’ Principle, enunciated by the Greek scientist of the same name.
Archimedes’ principle. Buoyancy force
Archimedes’ principle is a physical law established by the Greek scientist Archimedes, which describes the behavior of bodies immersed in fluids, either liquids or gases. This principle states that a body fully or partially immersed in a fluid will experience a vertical and upward thrust equal to the weight of the fluid displaced by the body. When a body is immersed in a fluid, either completely or partially, the fluid exerts a pressure on the body in all directions. The thrust is the resultant force of all these pressures and is equal to the weight of the fluid displaced by the body. If the weight of the object is less than the thrust, the body will float. If the weight is greater, the body will sink.
Relationship between buoyancy and density
Density is a physical property that relates the mass of an object to its volume, in the SI it is expressed in kilograms per cubic meter (kg/m³). It is a key factor in understanding buoyancy, as it determines whether an object sinks or floats when immersed in a fluid. This relationship is fundamental in the study of Archimedes’ principle and therefore, knowing the density of materials allows us to predict their behavior in water or other fluids.
Applications of the buoyancy principle
The principle of buoyancy is applied in many areas, such as ship design and construction. In the case of ships, for example, the shape and volume of the hull allows enough water to be displaced so that the total weight of the ship is less than the thrust generated by the water, thus ensuring its buoyancy.
The online buoyancy simulations on this page are an excellent tool to learn more about this important physics concept, to know Archimedes’ principle and to understand the relationship between buoyancy and density. Don’t miss them!

STEM OnLine mini dictionary
Apparent Weight
Net force acting on a submerged body, resulting from the difference between its real weight and the buoyant force (Pa = P – E) in the SI.
Archimedes’ Principle
Law stating that any body immersed in a fluid experiences an upward buoyant force equal to the weight of the displaced fluid.
Buoyant Force
Upward vertical force exerted by a fluid on a submerged body, calculated as E = ρ * V * g in the SI (in Newtons).
Center of Buoyancy
Point where the buoyant force is considered to be applied, coinciding with the center of gravity of the displaced fluid volume.
Density
Scalar quantity expressing the amount of mass per unit volume of a substance, measured in kg/m³ in the SI.
Displaced Volume
Space occupied by the fluid that has been moved aside by the body upon immersion, measured in m³ in the SI.
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Buoyancy simulations
Buoyancy I
With this simulation, you can easily explore the fundamental principles of flotation. Adjust the mass, volume, and material type of a block and observe how its behavior changes in different fluids. Check under what conditions an object sinks or floats, and see how relative density determines equilibrium, putting Archimedes’ principle into practice interactively.
Buoyancy II
This simulation takes the study of flotation a step further. Experiment with objects of different shapes and materials, change the fluid, and observe how the forces involved act: gravity, buoyancy, and contact. Explore more realistic scenarios, such as bottles and ships, to understand how Archimedes’ principle applies in everyday life and in the design of floating objects.
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“If I have seen further, it is by standing on the shoulders of giants”
Isaac Newton
Robert Boyle
–
Blaise Pascal
–
Become a giant
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“If I have seen further, it is by standing on the shoulders of giants”
Isaac Newton
Daniel Bernoulli
–
Archimedes
–
Become a giant
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Test your knowledge
What is buoyancy, and how does Archimedes’ Principle explain the behavior of objects in a fluid?
How are density, buoyant force and the behavior of submerged objects related?
Why do some objects float while others sink?
What does Archimedes’ Principle say in simple terms?
Why is buoyancy important in everyday life?
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