Surface tension

Examples of Surface tension in the following topics:

• Surface Tension

  • Surface tension is a contractive tendency of the surface of a liquid that allows it to resist an external force.
  • Surface tension is responsible for the shape of a liquid droplet.
  • If no force acts normal (perpendicular) to a tensioned surface, the surface must remain flat.
  • The surface tensions of a few common liquids and solutions are as follows, in dyne/cm (note the particularly high surface tension of water):
  • Note that the forces from the surface tension are symmetrical.

• Surface Tension and Capillary Action

  • Attractive forces between molecules cause effects such as surface tension and capillary action.
  • Surface tension is a contractive tendency of the surface of a liquid that allows it to resist an external force.
  • The cohesive forces among liquid molecules are responsible for the phenomenon of surface tension, as shown in .
  • Surface tension has the unit of force per unit length, or of energy per unit area.
  • If the diameter of the tube is sufficiently small, then the combination of surface tension (which is caused by cohesion within the liquid) and adhesive forces between the liquid and the container act to lift the liquid.

• Factors Affecting Pulmonary Ventilation: Surface Tension of Alveolar Fluid

  • The surface tension of alveolar fluid is regulated by pulmonary surfactant, allowing efficient respiration.
  • Surface tension is the force exerted by water molecules on the surface of the lung tissue as those water molecules pull together.
  • As the air inside the lungs is moist, there is considerable surface tension within the tissue of the lungs.
  • The force of surface tension in the lungs is so great that without something to reduce the surface tension, the airways would collapse after exhalation, making re-inflation during inhalation much more difficult and less effective.
  • The net result is that the surface tension of the lungs from water is reduced so that the lungs can still inflate and deflate properly without the possibility of collapse from surface tension alone.

• Surface Tension

  • Surface tension is the tendency of a liquid surface to resist forces applied to it.
  • Also, a paper clip or pin can be supported by the surface tension at a water air interface .
  • Therefore, the surface tension will be a property of the interface rather than simply the liquid.
  • In both cases, the vertical component of the surface tension is enough to support the weight of the object.
  • Summarize the cause for different surface tensions at a liquid's surface

• Water’s Cohesive and Adhesive Properties

  • Cohesion allows for the development of surface tension, the capacity of a substance to withstand being ruptured when placed under tension or stress.
  • Cohesion and surface tension keep the hydrogen bonds of water molecules intact and support the item floating on the top.
  • It's even possible to "float" a needle on top of a glass of water if it is placed gently without breaking the surface tension .
  • In another example, insects such as the water strider use the surface tension of water to stay afloat on the surface layer of water and even mate there.
  • The weight of the needle is pulling the surface downward; at the same time, the surface tension is pulling it up, suspending it on the surface of the water and keeping it from sinking.

• Factors Affecting Pulmonary Ventilation: Compliance of the Lungs

  • Compliance depends on the elasticity and surface tension of the lungs.
  • The lungs must also be able to overcome the force of surface tension from water on lung tissue during inflation in order to be compliant, and greater surface tension causes lower lung compliance.
  • Therefore, surfactant secreted by type II epithelial cells increases lung compliance by reducing the force of surface tension.

• Capillary Action

  • These cohesive forces are especially strong at the surface of a liquid, resulting in the phenomenon of surface tension.
  • If the diameter of the tube is sufficiently small, then the combination of surface tension (which is caused by cohesion within the liquid) and adhesive forces between the liquid and container act together to lift the liquid.
  • where T is the surface tension, $\rho$ is the density of liquid, g is the acceleration due to gravity, and r is radius of the tube.
  • The meniscus is the curve caused by surface tension in the upper surface of a liquid.
  • The curvature of the surface at the top of a column of fluid in a narrow tube is caused by the relative strength of the forces responsible for the surface tension of the fluid (cohesive forces) and the adhesive forces to the walls of the container.

• The Work of Breathing

  • The air-tissue/water interface of the alveoli has a high surface tension, which is similar to the surface tension of water at the liquid-air interface of a water droplet that results in the bonding of the water molecules together.
  • Surfactant is a complex mixture of phospholipids and lipoproteins that works to reduce the surface tension that exists between the alveoli tissue and the air found within the alveoli.
  • By lowering the surface tension of the alveolar fluid, it reduces the tendency of alveoli to collapse.
  • Surfactant works like a detergent to reduce the surface tension, allowing for easier inflation of the airways.
  • In emphysema, which mostly arises from smoking tobacco, the walls of the alveoli are destroyed, decreasing the surface area for gas exchange.

• Movement of Water and Minerals in the Xylem

  • Transpiration is caused by the evaporation of water at the leaf, or atmosphere interface; it creates negative pressure (tension) equivalent to –2 MPa at the leaf surface.
  • Water from the roots is pulled up by this tension.
  • This is called the cohesion–tension theory of sap ascent.
  • The cohesion-tension theory explains how water moves up through the xylem.
  • The cohesion–tension theory of sap ascent is shown.

• Partition and Religious Tensions