Question

Give reason as to why an iron needle sinks in water but a ship made of iron floats in water.

Answer 1

Hint To answer this question we should use the Archimedes’ Principle. The principal says that the greater will be the volume of the water displaced, the upthrust will be more. On the other hand, if the amount of water displayed is less then the upthrust will also be less on the object.

Complete step by step answer:
We know that the iron ship is constructed in such a way that it is mostly hollow from within.
Hence, the average density of the ship is less than that of water (i.e. less than$\dfrac{{1g}}{{c{m^3}}}$) whereas iron needle bring compact and its density is $\dfrac{{7.6g}}{{c{m^3}}}$ which is more than $\dfrac{{1g}}{{c{m^3}}}$ (density of water).

Hence, the needle sinks in water.

Note The Archimedes’ principle gives us an idea that when a body which is in a fluid is at rest then there will be a force acting on the body which will push the body upward. This force is known as the buoyant force and this force will be equal to the weight of the fluid that is displayed by the body. On the other hand, if the body is completely submerged in the fluid, then in that case the volume of the fluid that is displayed is equal to the volume of the body that is submerged.