- a plate
- a cup of milk
- food coloring
- soap solution
- cotton swab
How do I do ?
Take the plate and add milk in it. Drop a pinch of each food coloring one by one on the surface of milk at the center.Next add a drop of soap solution gently on the surface using a cotton swab.Soap has started its magical art work on milk. Amazing but simple.
Soap molecules reduce the surface tension of water and milk and separates the molecules from each other increasing the distance them.
Want to know more? Soap breaks the fore of attraction between the molecules of milk.The force of attraction is termed as” COHESIVE FORCE”.This force accounts for the stretched elastic membrane like nature of the liquid surface.
What is surface tension?
Molecules of the same substance are called “LIKE MOLECULES”.There are only air molecules above the surface of milk or any liquid taken in a vessel…meaning no like molecules above the surface.This leads to stronger force of attraction (cohesive force) among the molecules on the surface.Hence the stretched skin like nature of the surface of liquids called”SURFACE TENSION”.
Water molecule is made of one oxygen atom and two smaller hydrogen atoms.The hydrogen atoms hold a slight positive charge.This makes water molecule polar.Hydrogen atoms of one water molecule attract oxygen atoms of other water molecules.Thus each water molecule is pulled by other water molecule from all directions.Since there are no like molecules on the surface,they have more force of pull from the molecules below and sideways.The net cohesive force aligns the water molecules closer together on the surface.These molecules give the skin like nature for the surface of the liquid.
Soap molecules also have two ends.One end of the soap molecules moves away from water molecules to the surface. This reduces the force of attraction of the water molecules on the surface thereby breaking the surface tension.
The link to the video :