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Basics of Fluid Mechanics, 2014a

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138 CHAPTER 4. FLUIDS STATICS<br />

4.6.2 Surface Tension<br />

The surface tension is one <strong>of</strong> the mathematically complex topic and related to many<br />

phenomena like boiling, coating, etc. In this section, only simplified topics like constant<br />

value will be discussed.<br />

In one <strong>of</strong> the early studies <strong>of</strong> the surface tension/pressure was done by Torricelli 18 .<br />

In this study he suggest construction <strong>of</strong> the early barometer. In barometer is made from<br />

a tube sealed on one side. The tube is filled with a liquid and turned upside down into<br />

the liquid container.The main effect is the pressure difference between the two surfaces<br />

(in the tube and out side the tune). However, the surface tension affects the high. This<br />

effect is large for very small diameters.<br />

Example 4.31:<br />

In interaction <strong>of</strong> the molecules shown in Figure ?<br />

tension. Explain why this description is erroneous?<br />

describe the existence <strong>of</strong> surface<br />

Solution<br />

The upper layer <strong>of</strong> the molecules have unbalanced force towards the liquid phase. Newton’s<br />

law states when there is unbalanced force, the body should be accelerate. However,<br />

in this case, the liquid is not in motion. Thus, the common explanation is wrong.<br />

End Solution<br />

Fig. -4.47. A heavy needle is floating on a liquid.<br />

Example 4.32:<br />

Needle is made <strong>of</strong> steel and is heavier than water and many other liquids. However,<br />

the surface tension between the needle and the liquid hold the needle above the liquid.<br />

After certain diameter, the needle cannot be held by the liquid. Calculate the maximum<br />

diameter needle that can be inserted into liquid without drowning.<br />

Solution<br />

Under Construction<br />

End Solution<br />

18 Evangelista Torricelli October 15, 1608 October 25, 1647 was an Italian physicist best known for<br />

his invention <strong>of</strong> the barometer.

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