Calibration ring radius

Just as it is possible to float objects heavier than water on the surface of water, it is possible to pull the surface upward (increase the surface area) by the application of a suitable force, and thereby calculate the surface tension. The du Noiiy method makes use of a clean platinum ring of radius r that is placed on the liquid surface. The liquid, which wets platinum, tends to adhere to the ring, which is slowly raised by the application of a force, which is previously calibrated, until the net force pulling the ring upward exceeds the surface tension and the ring breaks from the surface. At that point the surface tension force, F, is 2ly, where 1 is the circumference of the ring, and since F = mg. 

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