1) The document summarizes an experiment conducted by a group of students to determine the surface tension force in a tapered vessel and communicating tubes, and its impact in real life applications. 2) The experiment measured how surface tension causes the water level to rise higher in narrow capillary tubes due to cohesive forces between water molecules. Adding soap reduces surface tension. 3) Surface tension is explained by molecular theory - molecules on the surface experience a maximum downward force due to an unbalanced distribution of neighboring molecules, giving the surface film its minimum energy configuration and tendency to minimize area.

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Petroleum Engineering Department
Faculty of Engineering
Koya University
Experiment No. : 3
Group: B
Group Members:
1-Sarwar Salam
2-Huner Mahdi
3-Savio Sarmad
4-Sangar Nasih

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Aim of the Experiment:
Determination of the Surface Tension force(ST) in the
Taper Vessel and in the Communicating Tubes also, and
its impact and influence on the applicable examples out
in our real life.
Finding the proportional type in between the distance of
the gaps and the Surface Tension

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Introduction:
The cohesive forces between liquid molecules are responsible
for the phenomenon known as surface tension (ST). The mol-
ecules at the surface do not have the similar neighboring atoms
on all sides and thus they cohere more strongly to those directly
associated with them on the surface. This forms a surface
“FILM” which makes it more difficult to move an object
through the surface than move it when it is completely immersed
(Figure 1). The same situation applies also at the interface of the
two liquids that do not mix together. In this case the term
interfacial tension (IFT) is used. There are several different units
for surface and interfacial tension; typically mN/m (which is
equivalent to dynes/ cm)isused.
(Figure 1)

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Theory:
The phenomenon of surface tension of a liquid can be explained on the
basisof molecular theory.
Consider a beaker containing water or liquid in which A, B and C arethe
molecules of liquid with their spheres of influence.
The molecule A is well inside the liquid. It is equally attracted by the
neighbouring molecules ofliquid. Hence, resultant cohesive force on the
molecule A is zero.
(Figure 2)
Consider the molecule B, just below the free surface of a liquid. The
maximum part of its sphere of influence is in liquid and some part of
sphere of influence is in air. Since the number of molecules of the liquid
in the lower half of the sphere is greater than that in the upper half,the
molecule B experiences resultant downward force.

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As the molecule approaches the surface, this downward cohesive force
on it increases because the number of molecules in the upper half of the
sphere decreases.
The molecule C is just on the free surface of the liquid. It's half of the
sphere of influence is in air and half of the sphere of influence is in
liquid. The upper half of the sphere of influence contains very few
molecules of the air.
So, the downward force, on the molecule becomes maximum. This
applies to all other molecules on the surface of the liquid. This
downward cohesive force per unit area of a liquid, is called its internal,
intrinsic or cohesive Pressure. If a molecule from the interior of the
liquid is brought to the surface, work has to be done against downward
cohesive force and its potential energy is increases. This shows that the
molecules on the surface possess greater potential energy than inside the
liquid.
In nature, a system tends to have minimum potential energy for stable
Equilibrium. Hence the liquid surface in trying to have the least
potential energy, tends to maintain least surface area. This tendency of
the free surface of the liquid at rest to have minimum area is called
surface tension.

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(Figure 3)
Procedure of performing the Taper vessel Experiment:
Fill the tapered vessel with water, as shown in the adjacent illustration.
(Figure 4)
The surface tension is especially noticeable in the range of smaller
dimensions. At such dimensions the surface tension acts so strongly that
it is able to raise the water below it.

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-TO MODIFIY the experiment….
Add a few drops of washing-up liquid to the water The line of the water
level immediately changes. Emulsifying agents in the washing-up liquid
are able to reduce the surface tension of the water. The surface tension
is dependent on the active substance pairing,
(Figure 5)

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B- Capillary tubes experiment
Aim of the experiment:
The water level in the capillary tubes rises as the tubes narrows.
(Figure 6)
The more the narrow the tube, the higher the level
the liquid is.

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Procedure of performing capillary communicating tubes:
Fill the capillary tubes with water. According to the law of
communicating tubes, the water level should be the same in all tubes.
As a result of the surface tension of the water, however, the water level
raises the narrower the tube. This property is termed the capillary effect
of water.
In visual terms, the surface tension of the water produces an upward
force, which is able to draw the head of water underneath it upwards.
With the same weight of water, the head of water can become higher the
"narrower" it is.
In reality the rise height depends not only on the surface tension of the
liquid, but also on its ability to coat the wall (adhesion). The adhesion
can be seen by the curved surface of the liquid.

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Discussion:
1- ) what is SFF stands for? And what is that?
-Ans.) SFF, is stands for Surface Tension Force. Which is (γ) is the
magnitude F of the force exerted parallel to the surface of a liquid
divided by the length L of the line over which the force acts:
γ =F/L
SI Unit of Surface Tension: N/m
2- ) what do we mean with Capillary tubes? And what
makes it differ from intercommunicating tubes?
Ans.) A tube with a very small diameter, which is called a capillary
tube. The difference between capillary tubes and interconnected tubes
is that the diameter is not limited in the connected tubes while tubes
diameter should very small in capillary tubes.
3- ) give a brief description of Cohesion?
Ans.) Molecules liquid state experience strong intermolecular
attractive forces. When those forces are between like molecules, they
are referred to as Cohesive force, for example the molecules of water
droplets are held together by cohesive forces, and the especially strong
cohesive forces at the surface constitute the Surface Tension.

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4- ) Write some examples of surface tension?
Ans.) -Walking on water
Small insects such as the water strider can walk on water because their weight is
not enough to penetrate the surface.
(Figure 7)
-Floating a needle
If carefully placed on the surface, a small needle can be made to float
on the surface of water even though it is several times as dense as water.
If the surface is agitated to break up the surface tension, then needle will
quickly sink.
-Soaps and detergents
help the cleaning of clothes by lowering the surface tension of the water
so that it more readily soaks into pores and soiled areas.

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5- ) what is the Surface tension of water?
Ans.) The surface tension of water is 72 dynes/cm at 25°C . It would
take a force of 72 dynes to break a surface film of water 1 cm long. The
surface tension of water decreases significantly with temperature as
shown in the graph. The surface tension arises from the polar nature of
the water molecule.
Hot water is a better cleaning agent because the lower surface tension
makes it a better "wetting agent" to get into pores and fissures rather
than bridging them with surface tension. Soaps and detergents further
lower the surface tension.

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References
1- ) http://hyperphysics.phy-
astr.gsu.edu/hbase/surten.html
2- )
http://scipp.ucsc.edu/~haber/ph5B/bubble.pdf
3- ) www.hyperphysics.edu
4- )http://water.usgs.gov/edu/surface-
tension.html
5- )
https://www.google.com/search?q=surface+te
nsion&tbm=isch&imgil=gzNtYkbao0UKzM%253
A%253BeHc51ce9i9gMxM%253Bhttp%25253A
%25252F%25252Fhyperphysics.phy-

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