Why Do Things Float?

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People wonder why massive ships and boats float on water even though they are very heavy. Some ask themselves why both one kilogram of wood and a hundred kilograms of wood can float on water. For a thing to float in water, it must be less dense than water. However, the number of atoms in an object and its buoyancy determine whether an object floats or sinks.

The Difference in Number of Atoms

‘œMatter’ consists of tiny particles that have some minute holes. These particles have a weight that makes them defy gravity. Different objects exhibit a different number of particles that result in different masses. The quantity of mass in a given quantity of space is what physics experts refer to as ‘œdensity.’ For example, fresh water differs in density when compared to salty water. For instance, take a liter of fresh water, pour it in a container, and measure its mass. Take the same quantity of salt water and measure its mass. You will realize that salty water is heavier than the fresh water. Salt water has some additional mass of salt particles. The additional salt particles explain why ocean water is denser than fresh water.

  • The Case of Clouds

Clouds float because they have less density than air. Steam has less density and, therefore, rises. The water droplets spread out to form clouds. The spread water droplets are very light compared to the air. The spread droplets make the clouds less dense than air and then eventually float.

  • The Case of Ships and Boats

A ship is made up of steel, whose material composition is denser than water. Nevertheless, an enormous ship is observed floating comfortably on the water. Experts fill most parts of the ship with materials that have less density than air. These materials make the whole ship light and, hence, floatable.


Floating of objects on the water depends on buoyancy. Also, swimmers float when they take in air and sink when they breathe out, though the weight is just the same. All these descriptions explain buoyancy. Buoyancy is an upward pressure that an object feels when placed on water. The upward force is as a result of water being denser than the object. The object has numerous microscopic air spaces that result in less density than that of water (1g/cm3). Nevertheless, objects sink when their weight exceeds upward force. When an object does not sink or rise in water, the object is neutrally buoyant.

The Archimedes’ Principle

The Archimedes’ principle states that the upward force exerted on an object is equal to the mass of the displaced amount of water. For this reason, one calculates buoyancy by finding the amount of volume of the liquid displaced by the object. After finding the volume, one can determine the amount of mass of the displaced object. For one to calculate the flotation needed to neutralize the upward buoyancy, we need to conduct a simple experiment and use the equation:


Just to conclude, objects that float on water have several factors that affect their buoyancy. These factors include density and the volume of the object put in the water. For example, a fish is denser than water; hence, it sinks. When one immerses the same egg in water with a small amount of salt, the egg floats but is still submerged. When one puts the same egg in water with a significant sample of salt, the egg floats completely on the water. Buoyancy is directly proportional to density. The extent of buoyancy also depends on the volume of the object immersed in the water. An object with a greater volume can disperse too much water as compared to an object with a small volume.

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