Surface Tension and Bubbles
The pressure difference between the inside and outside of a bubble depends upon the surface tension and the radius of the bubble. The relationship can be obtained by visualizing the bubble as two hemispheres and noting that the internal pressure which tends to push the hemispheres apart is counteracted by the surface tension acting around the cirumference of the circle. For a bubble with two surfaces providing tension, the pressure relationship is:
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Bubble PressureThe net upward force on the top hemisphere of the bubble is just the pressure difference times the area of the equatorial circle: The force of the surface tension downward on the entire circumference of the circle is twice the surface tension times the circumference, since two surfaces contribute to the force: This gives This latter case also applies to the case of a bubble surrounded by a liquid, such as the case of the alveoli of the lungs. |
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Surface Tension and Droplets
A water droplet can act as lens and form an image as a simple magnifier. The relatively high surface tension of water accounts for the ease with which it can be nebulized, or placed into aerosol form. Low surface tension liquids tend to evaporate quickly and are difficult to keep in an aerosol form. All liquids display surface tension to some degree. The surface tension of liquid lead is utilized to advantage in the manufacture of various sizes of lead shot. Molten lead is poured through a screen of the desired mesh size at the top of a tower. The surface tension pulls the lead into spherical balls, and it solidifies in that form before it reaches the bottom of the tower. |
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Capillary Action
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Capillary Action
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Capillary Action Calculation
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