Forces on a Partially Submerged Gate
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A gate, which is hinged at the bottom, is partially submerged under water, and a cable holds the gate closed. Use the sliders to set the angle of the gate, the weight of the gate and the water height. Use the buttons to change the units from klbF (force) and feet (US customary units) to kN and meters (SI units). Check the "show labels" box to display distances. The Demonstration displays the cable tension needed to support the gate. When the tension is too high (greater than 4.23 klbF or 18.82 kN), the cable breaks. 

[1] B. R. Munson, T. H. Okiishi and W. W. Huebsch, Fundamentals of Fluid Mechanics, 6th ed., Hoboken, NJ: John Wiley & Sons, 2009 pp. 57–60.