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Buoyancy. Archimedes’ Principle and density

28/03/2026

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.

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!

Explore the exciting STEM world with our free, online, simulations and accompanying companion courses! With them you’ll be able to experience and learn hands-on. Take this opportunity to immerse yourself in virtual experiences while advancing your education – awaken your scientific curiosity and discover all that the STEM world has to offer!

Buoyancy simulations

Buoyancy and density


This simulation allows us to understand the relationship between buoyancy and density. See how the density of an object changes as its mass or volume changes and how this affects its buoyancy.
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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.


Licencia de Creative Commons

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.


Licencia de Creative Commons

Archimedes’ principle


This simulation of Archimedes’ principle allows us to study the fundamental concepts of Archimedes’ principle. Change the mass and volume of the object and see what happens.






Buoyancy lab


Balance


Immerse the two objects in water. Why are they unbalanced? How do you achieve the point of equilibrium? Can you explain it?






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Buoyancy is the ability of an object to remain afloat or rise within a fluid. It is explained by Archimedes’ Principle, which states that any object fully or partially submerged in a fluid experiences an upward force equal to the weight of the fluid it displaces. This force arises because fluid pressure increases with depth, so the bottom of the object receives a stronger push than the top. The difference between these pressures creates the upward buoyant force. If this force is greater than the object’s weight, the object floats; if it is smaller, it sinks. Buoyancy is essential for understanding natural phenomena and technological applications such as ship design, submarine operation and density‑based measurement devices.
Density is crucial for predicting whether an object will float, sink or remain suspended in a fluid. According to Archimedes’ Principle, the buoyant force depends on the volume of displaced fluid. If an object is less dense than the fluid, it displaces enough fluid to generate a buoyant force greater than its weight, so it floats. If it is denser, the buoyant force is insufficient and it sinks. When densities match, the object stays in equilibrium. This relationship is fundamental in naval engineering, oceanography, meteorology and the design of instruments such as hydrometers. Understanding how density and buoyant force interact allows us to predict material behavior, optimize floating structures and analyze natural processes like iceberg stability.
It depends on density. If an object is less dense than the water, it displaces enough water to receive a buoyant force greater than its weight, so it floats. If it is denser, the buoyant force is too small and it sinks. That is why wood floats and rocks sink. It is not about how “heavy” something feels, but about how much mass it has compared to its volume.
It says that when you put an object in a liquid, the liquid pushes it upward with a force equal to the weight of the water the object displaces. If that upward push is stronger than the object’s weight, it floats; if not, it sinks. It is like the water giving the object a lift from below.
Buoyancy is essential for designing ships, submarines, buoys and floating structures. It also explains why hot‑air balloons rise, why we float more easily in saltwater and how aquatic animals stay at certain depths. In engineering, meteorology and oceanography, buoyancy helps predict how fluids and objects interact. It is a simple idea with huge practical impact.

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