![]() ![]() The colors represent the relative vorticity, a measure of turning or spinning of the air. Notice the circulation of the wind around the eye of the hurricane. Figure 14.24 shows velocity vectors describing the winds during Hurricane Arthur in 2014.įigure 14.24 The velocity vectors show the flow of wind in Hurricane Arthur. ![]() For example, wind-the fluid motion of air in the atmosphere-can be represented by vectors indicating the speed and direction of the wind at any given point on a map. Velocity vectors are often used to illustrate fluid motion in applications like meteorology. In a few examples, we examine an incompressible fluid-one for which an extremely large force is required to change the volume-since the density in an incompressible fluid is constant throughout. Viscosity is a measure of the internal friction in a fluid we examine it in more detail in Viscosity and Turbulence. An ideal fluid is a fluid with negligible viscosity. For this reason, we limit our investigation to ideal fluid s in many of the examples. Even the most basic forms of fluid motion can be quite complex. The rest of this chapter deals with fluid dynamics, the study of fluids in motion. The first part of this chapter dealt with fluid statics, the study of fluids at rest. Explain the consequences of the equation of continuity to the conservation of mass.Describe the relationship between flow rate and velocity.A tiny variation in one factor has an exaggerated (or nonlinear) effect on the flow.By the end of this section, you will be able to: It is difficult, but not impossible, to predict whether flow is turbulent or not when a fluid’s Reynold’s number falls in this range due to extremely sensitive dependence on factors like roughness and obstructions on the nature of the flow. ![]() A system is defined to be chaotic when its behavior is so sensitive to some factor that it is extremely difficult to predict. In fact, the flow of a fluid with a Reynolds number between 20 is a good example of chaotic behavior. The speed near the bottom of the flow ( between about 20, flow is unstable-that is, it can be laminar, but small obstructions and surface roughness can make it turbulent, and it may oscillate randomly between being laminar and turbulent. Notice that viscosity causes drag between layers as well as with the fixed surface. These resistive forces affect the way the fluid flows through the pipe.įigure 14.34 (a) Laminar flow occurs in layers without mixing. Friction also occurs between the different layers of fluid. For example, a fluid flowing through a pipe is subject to resistance, a type of friction, between the fluid and the walls. ![]() In this section, we introduce the forces of friction that act on fluids in motion. We explained that at low speeds, the drag is proportional to the velocity, whereas at high speeds, drag is proportional to the velocity squared. We also discussed drag and air resistance in that same chapter. Friction depends on the types of materials in contact and is proportional to the normal force. In Applications of Newton’s Laws, which introduced the concept of friction, we saw that an object sliding across the floor with an initial velocity and no applied force comes to rest due to the force of friction. Describe the conditions under which an object has a terminal speed.Use the Reynolds number for a system to determine whether it is laminar or turbulent.Calculate the Reynolds number for an object moving through a fluid.Explain how pressure drops due to resistance.Calculate flow and resistance with Poiseuille’s law.By the end of this section, you will be able to: ![]()
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