The number of molecules at the surface is proportional to the surface area. The resistance to flow of a liquid is called the liquid's viscosity . The viscosity of the oil lubricating your car engine is an important part of engine performance and longevity. You change your oil when the viscocity of the engine oil 'breaks down' or decreases. You use in different oil in your car during the winter than in the summer because viscocity is effected by temperature.
Viscosity is a measure of the ease with which molecules move past one another.
Viscosity depends on the attractive force between the molecules. Viscosity decreases with increasing temperature - the increasing kinetic energy overcomes the attractive forces and molecules can more easily move past each other. Surface tension determines the pressure inside of a bubble . Our understanding of surface tension was made more complete by our understanding of intermolecular forces, i.e., the energetics of making and breaking of molecular 'neighbors'. Such energies can be determined experimentally by calorimetry , or the measure of the heat flow during a chemical or physical process.