Water/Food colours (any four colours)
4 drinking water glasses
1 small glass
Fill the 4 glasses with equal amounts of water.
Add one spoon of sugar to the first glass, two spoons to the second glass, three spoons to the third glass, and four spoons to the fourth glass. Make it a point that the sugar is completely dissolved. (If not, heat the water so that the sugar dissolves completely. Heat the water only under adult supervision.)
Add different food/water colours to the 4 different glasses with the help of the dropper. Add red to the glass with one spoon of sugar, yellow to the glass with two spoons of sugar, green to the glass with three spoons of sugar and blue to the glass with four spoons of sugar.
Now, with the help of the dropper, pick up some green coloured water and drop it in the glass with blue coloured water. Similarly, pick up some water from yellow and red one after the other from the dropper and put it in the glass containing blue sugar water.
We can notice that colours sit one above the other like a rainbow, without mixing.
How it works? It is density which plays an important role here. The differently coloured solutions do not mix with each other because of the difference in their densities. The solution with 4 spoons of sugar is denser than the one with 3 spoons of sugar. Thus, they do not mix. Similarly, none of the solutions mix with each other, forming layers of different colours, forming a rainbow of colours in a glass.