![]() Surface Tension FBD: Force diagrams showing the direction of forces for water supporting a water strider (insect) foot and a pin. Also, a paper clip or pin can be supported by the surface tension at a water air interface. This effect is visible in nature with water strider insects that are able to walk on water. This effect is a result of cohesion of the molecules of the liquid causing the surface of the liquid to contract to the smallest area possible. Surface tension is the tendency of a liquid surface to resist forces applied to it. ![]() Summarize the cause for different surface tensions at a liquid’s surface.Ideal Fluid: Applies to an ideal fluid (inviscid, incompressible) Toricelli’s Law: The exit velocity depends on the height of the fluid above the exit hole. The exit velocity can be increased by capping the top of the reservoir and pressurizing it. As the height in the reservoir decreases, the exit velocity will decrease as well. ![]() Ī simple experiment to test Torricelli’s law involves filling a soda bottle with water and puncturing the bottom with a small hole (about 1 cm in diameter). The result is that the velocity acquired by the fluid is the same that a body would acquire when simply dropped from the height h t. Due to the assumption of an ideal fluid, all forces acting on the fluid are conservative and thus there is an exchange between potential and kinetic energy. Where again h t is the height difference between the top of the reservoir and the exit hole. This can be solved for the exit velocity, resulting in, If we assume both the top of reservoir and the exit are open to the atmosphere, the zero for potential energy is at the exit hole, and the fluid velocity at the top of the reservoir is essentially zero (large reservoir, small hole), we arrive at Where subscript t implies evaluation at the top of the reservoir and subscript e implies evaluation at the exit.
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