Why does it happen? A ship dips to a larger depth in fresh water as compared to marine water.

Hint: Buoyant force is the main factor that is responsible for floating and sinking of substances in liquids. Linking density with buoyant force is necessary to understand this question. Properties of liquid are important to understand the question and the solution.

Complete step by step answer:
Buoyant Force is an upward force applied by the liquid on any object placed in it. It acts opposite to the weight of object and is given by formula,
\[{F_B} = \rho gV\]
Where, ${F_B}$= Buoyant Force, $g$ = acceleration due to gravity, $V$ = Volume of liquid displaced and $\rho $= density of liquid.

From the formula it is clearly evident that buoyant force is dependent on volume of liquid displaced and density of liquid in which object is placed. Now according to the question the ship is present in two water systems (marine and freshwater). Due to salinity in marine water the density of this water system is increased as compared to fresh water i.e., density of marine water > density of freshwater

It is clearly evident from the formula of buoyant force that buoyant force is directly proportional to density of liquid. So due to the high density of marine water it will apply greater buoyant force than fresh water systems. And greater the buoyant force more will be the upward push on the object and lesser will be the depth of the ship in water.

Hence, we can conclude that; due to lesser density of freshwater, the buoyant force is reduced and resultant will be increased in depth of ship dipped.

Note: Buoyancy force can be of 3 types dependent on the substance density and liquid density (positive, negative and neutral). If the body is floating it is positive buoyancy, if body is sinking it is negative buoyancy and when weight of body equals to fluid displaced it is neutral buoyancy. Each case is density dependent and it is crucial to understand the differences between all cases.