Why a glass rod coated with wax does not become wet when dipped in water?
Answers
Not only a glass rod but anything that is coated with wax do not get wet. This is due to Property called as angle of contact. Basically angle of contact is ,
The angle between the tangent to the liquid surface at the point of contact, and solid surface, inside the liquid is called angle of contact for a given pair of solid and liquid.
As angle of contact of water and wax coating object will be obtuse, i. e, (>90°) the wax coated object acts as a wafter proofing agent.
Water does not wet waxed surfaces because the cohesive forces within the drops are stronger than the adhesive forces between the drops and the wax. Water wets glass and spreads out on it because the adhesive forces between the liquid and the glass are stronger than the cohesive forces within the water.