WHAT IS SURFACE TENSION?
Surface tension is a property of liquids that
arises from unbalanced molecular cohesive forces at or near
a surface. At an air water interface the surface tension results
from the greater attraction of water molecules to each other
(due to cohesion) than to the molecules in the air (due to
adhesion). The net effect is an inward force at its surface
that causes water to behave as if its surface were covered
with a stretched elastic membrane. Because of the relatively
high attraction of water molecules for each other, water has
a high surface tension.
Surface tension arises from the strong interactions
between water molecules, called hydrogen
bonding. It is this strong interaction which also manifests
in the other unusual property of water such as its high boiling
Surface tension of water also manifests as
the so-called hydrophobic effect. Hydrophobic molecules tend
to be non-polar and, thus, prefer other neutral molecules
and non-polar solvents--"water- hating". A hydrophilic
molecule or portion of a molecule is one that has a tendency
to interact with or be dissolved by water and other polar
substances --"water-loving" -- See also: How
does soap work?
cohesive forces between molecules in a liquid are shared
with all neighboring molecules. Those on the surface
have no neighboring molecules above and, thus, exhibit
stronger attractive forces upon their nearest neighbors
on and below the surface.
molecules in center of water, all attractive forces
the surface, molecules have unbalanced surface ... fluid
tries to minimize it's surface area. This is why water
forms a drop. the surf race tries to minimize area
inside liquid is under pressure.
edited from USGS.gov
meniscus is the curve in the upper surface of a liquid
close to the surface of the container or another object.
It is caused by surface tension. It can be either convex
or concave, depending on the liquid and the surface.
shown on Left -- a concave meniscus occurs when the
particles of the liquid are more strongly attracted
to the container than to each other, causing the liquid
to climb the walls of the container. This occurs between
water and glass.
shown on Right -- a convex meniscus occurs when the
particles in the liquid have a stronger attraction to
each other than to the material of the container. Convex
menisci occur, for example, between mercury and glass
Cohesive attraction or cohesive force is the action
or property of similar molecules sticking together,
being mutually attractive. Cohesion, along with adhesion
(attraction between unlike molecules), helps explain
phenomena such as meniscus, surface tension and capillary
edited from Reading the Meniscus (Jleedev) Wikipedia.
Examples of surface tension in action include
--formation of liquid droplets,
--the ability of a needle to float on water,
--why bubbles are round
--soap being used the break up water tension.
Surface tension has the dimension of force
per unit length, or of energy per unit area. The two are equivalent—but
when referring to energy per unit of area, people use the
term surface energy—which is a more general term in
the sense that it applies also to solids and not just liquids.
Surface tension, usually represented by the
symbol γ, is measured in force per unit length. Its
SI unit is newton per meter.
In terms of energy: surface tension --gamma--
of a liquid is the ratio of the change in the energy of the
liquid to the change in the surface area of the liquid (that
led to the change in energy).
for a derivation of the formula see: wikipedia
This work W can be interpreted as being stored
potential energy. Thus, surface tension can be also measured
in the SI system as joules per square meter. Since mechanical
systems try to find a state of minimum potential energy, a
free droplet of liquid water will try to assume a spherical
shape, which has the minimum surface area for a given volume.
WHAT IS CAPILLARY ACTION?
THIS: FILL A GLASS WITH DILUTED GRAPE JUICE AS SHOWN BELOW.
FOLD A PAPER TOWEL TO CONNECT THE TWO GLASSES...OBSERVE
WHAT HAPPENS OVER SEVERAL HOURS...
20 MINUTES -- WATER IS MOVING UP THE PAPER TOWEL
2 HOURS -- MOSTLY WATER HAS MOVED INTO THE SECOND GLASS
4 HOURS -- SOME PIGMENT HAS MOVING
action occurs because water molecules bond each other strongly
due to forces of cohesion and adhesion where water molecules
are attracted and stick to other substances such as glass
or paper. Adhesion of water to the surface of a material will
cause an upward force on the liquid. The surface tension acts
to hold the surface intact. Capillary action occurs when the
adhesion to the surface material is stronger than the cohesive
forces between the water molecules. The height to which
capillary action will take water is limited by surface tension
in the photos above the effect that gravity has on capillary
action. Water being a polar molecule and low mass moves easily
up the paper. The diluted grape juice contains several non-polar
red pigments which are not very soluble in water and do not
migrate with the solvent.
If one takes a small capillary tube an inserts
it in water and the tube does not have a vacuum like a barometer
but is open at top, water will start to rise up. Water wants
to stick to the glass and surface tension will push the water
up, until the force of gravity prevents further rise.
is the result of cohesion of water molecules and adhesion
of those molecules to a solid material. In the case
of a glass tube inserted in water with openings at both
ends, as the edges of the tube are brought closer together,
such as in a very narrow tube, the liquid will be drawn
upward in the tube. The more narrow the tube, the greater
the rise of the liquid. Greater surface tension and
increased ratio of adhesion to cohesion also result
in greater rise.
for water in a tube all values are constant except r,
radius, the height of rise is solely dependent on
the radius of the tube.
action is due to the pressure of cohesion and adhesion
which cause the liquid to work against gravity.
action (sometimes capillarity, capillary motion,
or wicking) is the ability of a liquid to flow in narrow spaces
without the assistance of, and in opposition to, external forces
ACTION IN PLANTS
The plant on the left was not watered for 2 days and
allowed to wilt.
VIDEO OF CAPILLARY
ACTION IN PLANTS
Time Lapse photography was done over a time span of
2 hours after the plant was watered and slowly comes
back to life...demonstrating capillary action
----Click on Image----
Capillary action is what draws the water from soil
back up to the leaves.
action is the process that plants use to pull water and mineral
up from the ground. It is is the movement of liquid along
a surface of a solid caused by the attraction of molecules
of the liquid to the molecules of the solid. The molecules
of the water (liquid) are attracted to the molecules inside
the stem similar to capillary action of water in a glass tube.
There are three forces involved with the process
of capillary action in plants.
1) Adhesion, the process of attracting two
dissimilar molecules. For plants, adhesion allows for the
water to stick to the organic tissues of plants.
2)Cohesion keeps similar molecules together.
For plants, cohesion keeps the water molecules together.
tension is a property of liquids that arises from unbalanced
molecular cohesive forces at or near a surface..