Measurement of surface tension of water by capillarity                  

Groups:

Measurement of surface tension of water by capillarity:

        Date of measure 13:00-13.03.2019

Tools:

        Beaker, capillary pipe, ruler, support foot, gripper, iron bars, water, thermometer, smartphone (We used the capillary pipe of 5 mm and 3mm diameters).

Description of measurement method:

    Surface tension:

       The surface tension is the name of the effect that causes the surface layer of a liquid to behave like a flexible membrane. The surfaces of all liquids behave as though they are covered with a stretched membrane. In this case, the liquid surface contracted to cover the smallest possible area. The mathematical model of surface tension is the force per unit length.

Y= F / L

       The unit is N / m, but is also indicated in dyne / cm because the force is small. This means that you need to apply few dyne force to break a 1 cm long membrane.

       The cause of surface tension is the cohesion force between liquid molecules. The molecules in the interior of the fluid are surrounded by other liquid molecules. A molecule remains under the effect of an equal amount of cohesion force. But there is no liquid molecule on the upper side of the molecules with liquid and air boundaries. Therefore, the liquid molecules at the boundary and the cohesion strength of the molecules next to them are stronger.

        The floating pin floats on the water due to surface tension.

          Water flies do not sink into the water due to surface tension.

                  Capillarity:

       Capability is a matter of attracting another substance to itself. It can be easily observed in the transmission system of a plant. The gravity of a liquid and another substance at the molecular level is due to the fact that the liquid is stronger than the gravitational force between its molecules. This effect causes the liquid surface to be concave at the part where the liquid touches a vertical surface. The same effect is seen in the absorption of water such as sponge

    Capillary tubes are the most widely used test setup for observing capillaries. If a tubular pipe is vertically immersed in water, the water rises in the pipe. A concave meniscus is formed on the water surface in the pipe. The surface tension draws the fluid arm up until the gravitational forces are in equilibrium. Because the weight of the liquid column is proportional to the square of the radius of the tube and the radius of the tube between the liquid and the pipe, a narrow tube carries the liquid upwards from a wide pipe.Capillarity varies depending on density, type of liquid and capillary tube, temperature, capillary diameter and gravity.

Relationship between surface tension and capillarity :

       The sum of the vertical component of the surface tension force to the circumference of the capillary tube is equal to the weight of the rising water in the pipe

   ın this case, surface tension is Y=h.d.g.r/(2.cosϴ).     .                                    

Our measurements:

       We have prepared our measuring device. We've glued a transparent ruler near the capillary tube. We took photos of the rising water in the capillary tube with the smartphone. We have downloaded the protractor program from google play to smart phone. We determined the amount of water rise by comparing it with the millimetric partitions of the ruler in the picture. We also determined the angle of the glass tube with the protractor program. We measured the water temperature at 21 0C. Water density was 1000 kg / m3 and gravity acceleration was 9.8 m / s2.  

      We took the height from the middle of the meniscus. We have calculated the surface tension of the water by substituting the values ​​of Y = hdgr / (2.cosϴ).

            Y=0,0723±0,0047  N/m

Conclusion and discussion :

      Surface tension for liquids is important in daily life. For example, the surface tension low water makes better cleaning. To reduce surface tension, the temperature of the water is increased or detergent added to the water.

Surface tension of water can be found by various methods. One of these methods is the capillary method. (Drop, frame, etc.).     In the literature, the surface tension of water at 20 0C is given as Y=0,0728 N / m. The average value we found was close to it. Our value is Y=0,0723±0,0047 N/m.  The difference may be due to various measurement errors.                

Mehmet Taşkan

Web:  www.fizikevreni.com

e-mail: fizikevreni@mynet.com