The surface tension of water is 72 dynes/cm at 25°C . It would
take a force of 72 dynes to break a surface film of water 1 cm long. The surface
tension of water decreases significantly with temperature as shown in the graph.
The surface tension arises from the polar
nature of the water molecule.
Hot water is a better cleaning agent because the lower surface tension makes
it a better "wetting agent" to get into pores and fissures rather than bridging
them with surface tension. Soaps and detergents further lower the surface
tension.
