Tension Superficial
Diagrams
Free body diagram of a particle in a body of water :
This free body diagram of a particle inmersed in a fluid shows the forces acting on the particle, When the particle is on the surface adhesive forces to air are smaller than cohesive forces.
Surface tension variation with temperature :
From the Figure it can be seen that surface tension decreases as temperature increases. This is because cohesion forces decrease with thermal agitation.
Contact angle free body diagram :
Another phenomenon that influences the rise or drop of a fluid in a capilary tube is the relative value of the adhesion forces between the wall and the fluid, and the cohesive forces of the fluid. The ratio of these forces determines the angle that the fluid forms when it comes into contact with the solid. If the angle is small the liquid wets the solid and a concave meniscus is formed in a capilary tube.
Soil moisture retention curves:
Interconnected pore space in soils hold water due to surface tension effects. The pores in a soil act like capilaries that absorb and retain water. The smaller the pore, the larger the energy with which water is retained in the soil (large pores are easy to drain, and small ones are difficult to drain). The Figure shows soil mosture content versus retention energy. Note how soil texture influences shape of the curve. Soils with large pores tend to hold less water and drain quicker than soils with fine textures.
Surface tension of water and other liquids
Because of the large cohesive forces of water, surface tension of water is generally high when compared to other liquids.
Free body diagram of DuNoy's ring
Dunoy's ring is a common method used to measure surface tension. The ring is place in the surface of the liquid allowing the liquid to adhere to the ring. The force required to pull the ring from the surface of the liquid is carefully applied and measured.
Capilary rise
When water comes into contact with a capilary tube a meniscus will be formed resulting in a net upward force. As water climbs into the capilary, the weigh of the water column will offset the capilary force until equilibrium is reached. The smaller the diamert of the capilary the higher the rise.
NOTE
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