Why do some Objects sink in Water
Those objects which have density more than water sink in water
We can also say that those having Relative Density more than 1 sink in water
Example
Iron floats in water because Iron has more density than water
(Density of iron is 7800 kg/m 3 but water is 1000 kg/m 3
Relative Density of Iron = Density of iron/Density of Water = 7800/1000 = 7.8
We can also say that since relative density of object is more than 1, it sinks in water
Reason for Sinking
The object sinks in water because buoyant force is less than force exerted due to weight of object due to its high density
Why do Some Objects float in water
Those objects which have density less than water float in water
We can also say that those having Relative Density less than 1 sink in water
Example
Cork floats in water because cork has less density than water
(Density of Cork is 240 kg/m 3 but water is 1000 kg/m 3
Relative Density of Cork = Density of Cork/Density of Water = 240/1000 = 0.24
We can also say that since relative density of object is less than 1, it floats in water
Reason for Floating
The object floats in water because buoyant force is more than force exerted due to weight of object due to its low density
Ships are made of iron built still it floats in Water. Why?
Ship is made of iron and steel
But is a hollow object containing lot of air
Air has lower density than water
So upward buoyant force of water is high which keeps ship afloat
Questions
NCERT Question 21 - The volume of 50 g of a substance is 20 cm 3 . If the density of water is 1 g cm –3 , will the substance float or sink?
