Why do heavier objects not always sink in water?

Heavier objects do not always sink in water due to their density relative to the density of water.

In more detail, whether an object sinks or floats in water is determined by the principle of buoyancy, which is related to the densities of the object and the fluid in which it is submerged. Density is defined as mass per unit volume. If an object is denser than the fluid, it will sink. If it is less dense, it will float.

Water has a density of 1 gram per cubic centimetre (g/cm³) at standard temperature and pressure. If an object has a density greater than 1 g/cm³, it will sink in water. If its density is less than 1 g/cm³, it will float. This is why a heavy steel ship can float on water. Although steel is much denser than water, the ship is designed to displace a volume of water that weighs more than the ship itself. The air inside the ship reduces its overall density, making it less dense than the water it displaces.

The principle of buoyancy was first discovered by the ancient Greek scientist Archimedes. According to Archimedes' principle, an object submerged in a fluid experiences an upward force equal to the weight of the fluid displaced by the object. This is why objects seem to weigh less in water than in air.

In conclusion, the weight of an object is not the only factor that determines whether it will sink or float in water. The object's density relative to the water's density is the key factor. This principle is fundamental in many areas of physics and engineering, including the design of ships and submarines.