Chapter VIII Fluid Mechanics

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1 Chapter VIII Fluid Mechanics
Density and Pressure Pressures in a fluid at Rest Buoyancy Fluid Flow

2 A fluid is a collection of molecules that are randomly arranged and held together by weak cohesive forces and by forces exerted by the walls of a container. Both liquids and gases are fluids. A. Density and Pressure The density of a substance is defined as its mass per unit volume = m/V = dencity m = mass V = Volume F = force A = surface area p = Pressure

3 B. Pressures in a Fluid at Rest
The pressure p at a depth h below the surface of a liquid open to the atmosphere is greater than atmospheric pressure (po) by an amount gh

4 Pascal’s law: A change in the pressure applied to a fluid is transmitted undiminished to every point of the fluid and to the walls of the container. Because the increase in pressure is the same on the two sides, a small force Fl at the left produces a much greater force F2 at the right

5 1. Totally Submerged Object
C. Buoyancy Have you ever tried to push a beach ball under water? This is extremely difficult to do because of the large upward force exerted by the water on the ball. The upward force exerted by water on any immersed object is called a buoyant force. 1. Totally Submerged Object B = Buoyant force Fg = Force of gravity/weight 2. Floating Object Vf is the volume of the fluid displaced by the object (this volume is the same as the volume of that part of the object that is beneath the fluid level) Fg = B o Vo g = f Vf g

6 D. Fluid Flow Ideal fluid The fluid is nonviscous. In a nonviscous fluid, internal friction is neglected. An object moving through the fluid experiences no viscous force. The flow is steady. In steady (laminar) flow, the velocity of the fluid at each point remains constant. The fluid is incompressible. The density of an incompressible fluid is constant. The flow is irrotational. In irrotational flow, the fluid has no angular momentum about any point A1 v1 = A2 v2 = constant The equation of continuity

7 Bernoulli’s Equation

8 MEKANIKA FLUIDA

9 Fluida Statik Fluida merupakan istilah untuk zat alir.
Fluida statik adalah fluida yang tidak bergerak. Contoh fluida statik misalnya air di gelas, air di kolam renang, dan air danau. 1. Fluida ideal Fluida ideal adalah fluida yang memiliki ciri-ciri sebagai berikut. a. tidak kompresibel (volumenya tidak berubah karena perubahan tekanan) b. berpindah tanpa mengalami gesekan (viskositasnya nol) 2. Fluida sejati Fluida sejati memiliki ciri-ciri sebagai berikut. a. kompresibel b. berpindah dengan mengalami gesekan (viskositasnya tertentu)

10 1. Kohesi dan Adhesi Gaya kohesi adalah gaya tarik-menarik antarmolekul sejenis. Sedangkan gaya adhesi adalah gaya tarik-menarik antarmolekul yang tidak sejenis. Meniskus cembung menimbulkan sudut kontak tumpul (> 90) Meniskus cekung menimbulkan sudut kontak lancip (< 90°)

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