A body sinks in water when

A body sinks in water when its density is greater than the density of water. According to Archimedes' Principle, an object submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces [1]. If the object's density is higher than the fluid's density, its weight will exceed the maximum possible buoyant force, causing it to sink [2]. Conversely, if the object is less dense than the fluid, it will rise or float [2]. For example, a stone sinks because it is denser than water, while an air bubble rises because it is less dense [2]. Therefore, the condition for sinking is that the density of the water must be less than the density of the body. This relationship between average density and buoyancy determines the vertical movement of objects in any fluid.

Sources

1. [1] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 5: Exploring Forces > Activity 5.13: Let us investigate > p. 76
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 22: Vertical Distribution of Temperature > Adiabatic Process: Temperature Changes In A Parcel of Rising or Falling Air > p. 296