Surface tension
Surface tension is the force that makes a liquid surface behave like a stretched skin. It lets insects walk on water and pulls droplets into spheres. It is measured as force per unit length (N/m) or, equivalently, energy per unit area (J/m²).
Laboratory values are normally quoted in mN/m or dyn/cm, which are the same size. Water at 20 °C has a surface tension of about 72.8 mN/m, ethanol about 22 mN/m and mercury about 485 mN/m. Soaps and detergents work partly by lowering the surface tension of water.