force per unit area is a measure of pressure.
force per unit area is a measure of pressure.
force per unit area is a measure of?
pressure
consider a column of water in hydrostatic equilibrium. all the forces on the water are in balance and the water is motionless. on any given drop of water, two forces are balanced. the first is gravity, which acts directly on each atom and molecule inside. the gravitational force per unit volume is , where is the gravitational acceleration. the second force is the sum of all the forces exerted on its surface by the surrounding water. the force from below is greater than the force from above by just the amount needed to balance gravity. the normal force per unit area is the pressure . the average force per unit volume inside the droplet is the gradient of the pressure, so the force balance equation is
momentum
surface stress was first defined by josiah willard gibbs (1839-1903) as the amount of the reversible work per unit area needed to elastically stretch a pre-existing surface. a suggestion is surface stress define as association with the amount of the reversible work per unit area needed to elastically stretch a pre-existing surface instead of up definition. a similar term called “surface free energy”, which represents the excess free energy per unit area needed to create a new surface, is easily confused with “surface stress”. although surface stress and surface free energy of liquid–gas or liquid–liquid interface are the same, they are very different in solid–gas or solid–solid interface, which will be discussed in details later. since both terms represent a force per unit length, they have been referred to as “surface tension”, which contributes further to the confusion in the literature.
surface stress