#density
#float#sink
#engaging_activities

Take some fruits like chikoo orange, banana, apple, pomegranate, lime, lemon etc. and a bowl of water.
Put the fruits in water one by one like a chikoo followed by an orange.
You will be surprised, the chikoo #sinks but the orange despite being bigger floats.
Let's try with an apple. It #floats !
A banana floats too.
Pomegranate also floats.
Try some other fruits too , like lime and lemon.
The lime floats while the lemon sinks.
Moreover the lime with rind floats while the one without rind sinks.
So what we see here that some fruits sink in water while some float. Whether an object floats or sinks depends upon a characteristic property of the object called #density.
Density is the #mass_per_unit _volume.
To calculate density we divide mass of the object by its volume.
Thus the object which has more mass in equal volume is more #denser.
SI unit of density is #kg/ m³
The objects having density lower than that of water float while those with density higher than water sink.
The fruits which have density less than water so they float in water. While chikoo and lemon being denser than water, sink in it.
Put a lemon in water. It sinks to the bottom.
Add some salt into water and see what happens.
The lemon slowly rises up and later on floats in water.
Why did this happen?
The salt dissolved in water and this increased the density of water.When most of the salt was dissolved the lemon comes up to the top.
So the density of the lemon is less than salt water but more than normal, right?
We compared the densities of different solids with the density of water. But different liquids too have different densities.
Let's take some dish washing liquid soap, water and vegetable oil in a glass. Allow them to settle for some time. We get different layers of the liquids. Liquid soap being the most dense of the three settles at the bottom, water forms the middle layer, vegetable oil forms the top layer. Thus liquid soap's density is more than water but oil's #density is less than that of water Here we are comparing density of these two liquids with respect to water.
Such comparison of density of one substance with respect to the other is called #relative _density or #specific_gravity. Thus relative density is the ratio of density of a substance to the density of the reference substance.
Since it is the ratio of two densities relative density has no unit.
Here the reference substance is water.Density of water is around 1000 kg/m3 , however it can vary depending on the temperature. Density of vegetable oil is around 950 kg/ m³
So relative density of vegetable oil is 0.95 and since this value is less than 1, oil floats on water.
While relative density of soap is greater than 1 hence it sinks.
You know that ice floats on water because its relative density at 4⁰C is 0.92
Wood has relative density 0.8.
While glycerine has relative density 1.26, so it sinks in water.