Drag Force
Drag force is a resistance force exerted on an object moving through a fluid, such as air or water. It opposes the object's motion and is influenced by the object's shape, size, and speed, as well as the properties of the fluid. Drag force is an important concept in understanding the behavior of objects in fluid dynamics and is crucial in various engineering and scientific applications.
6 Key excerpts on "Drag Force"
eBook - ePubUnderstanding Aerodynamics
Arguing from the Real Physics
- Doug McLean(Author)
- 2012(Publication Date)
- Wiley(Publisher)
...Even for well-designed streamlined bodies, the pressure contribution is rarely less than about 10% of the total drag. For airfoils, the pressure contribution to drag is generally larger than this, as we'll see in Section 7.4.2.The pressure contribution to the force can be clearly interpreted as lift (Equation 5.4.1) or drag ("Equation 6.1.1) only after it has been integrated over the entire surface of a closed body. If the pressure contribution is integrated over only a portion of a body, interpreting the result as “lift” or “drag” is problematic. We'll see the reasons for this when we consider the issue in detail as it applies to drag in Section 6.1.3.Newton's third law requires that the force exerted by the flow on the body is reciprocated by an equal-and-opposite force exerted by the body on the flow. And the equations of motion require that this force must have manifestations in the flowfield. Generating lift requires setting some of the fluid in motion, as we'll discuss in great detail in Chapters 7 and 8. Drag requires either generating lift in 3D or the presence of the dissipative processes associated with viscosity, as we'll see in Chapter 6....
eBook - ePub- Mark Dusenbury, Gary Ullrich, Shelby Balogh(Authors)
- 2016(Publication Date)
- Aviation Supplies & Academics, Inc.(Publisher)
...Like lift, we take the drag of each individual component and combine them into a single aircraft drag magnitude. And like lift, drag acts through the aircraft center of pressure. Drag is the force that resists the movement of an aircraft through the air. There are two basic types: parasite drag and induced drag. Induced drag is the component vector of lift that acts parallel to the flight path but opposite its direction. In contrast, parasite drag is a force that results from an object’s shape and texture as it moves through the air. Parasite drag is not related to the production of the lift necessary to sustain powered flight. Review Questions Describe lift and explain some of its basic principles. What is meant by the term “magnitude of weight”? Describe thrust and how it is produced. When are the four forces in flight in equilibrium? Describe drag and explain the two types....
eBook - ePubThe Really Useful Science Book
A Framework of Knowledge for Primary Teachers
- Steve Farrow, Amy Strachan(Authors)
- 2017(Publication Date)
- Routledge(Publisher)
...When objects are slowed down by frictional forces in a fluid, the effect is known as drag – air resistance, for example, is a form of drag. When friction is overcome, and movement results, two other effects can be noticed. First, the force applied in order to overcome the force of friction causes the conversion of energy as heat – moving surfaces heat up when they are rubbed together. Second, moving surfaces that are in contact tend to suffer from wear. The force of friction, like the force of gravity, is always present on Earth. In everyday terms, it is practically impossible to produce a completely friction-free system, although, in industry and commerce, much time, money and effort are spent in the attempt to minimize the effects of frictional forces between materials. The effects of the force of friction can be both advantageous and disadvantageous. WORKING SCIENTIFICALLY Grippy shoes Children can compare how much friction different shoes have by measuring the force it takes to move them across a surface. Once children have compared a range of shoes (from walking shoes to high-heel shoes to ballet shoes), they can then design their own pair of shoes, considering both their material and sole pattern. Some advantages of friction are as follows: • Frictional forces allow us to move...
eBook - ePub- Martin J. Rhodes, Martin J. Rhodes(Authors)
- 2013(Publication Date)
- Wiley(Publisher)
...2 Single Particles in a Fluid This chapter deals with the motion of single solid particles in fluids. The objective here is to develop an understanding of the forces resisting the motion of any such particle and provide methods for the estimation of the steady velocity of the particle relative to the fluid. The subject matter of the chapter will be used in subsequent chapters on the behaviour of suspensions of particles in a fluid, fluidization, gas cyclones and pneumatic transport. 2.1 MOTION OF SOLID PARTICLES IN A FLUID The Drag Force resisting very slow steady relative motion (creeping motion) between a rigid sphere of diameter x and a fluid of infinite extent, of viscosity μ is composed of two components (Stokes, 1851): (2.1) (2.2) (2.3) where U is the relative velocity. This is known as Stokes’ law. Experimentally, Stokes’ law is found to hold almost exactly for single particle Reynolds number, Re p ≤ 0.1, within 9% for Re p ≤ 0.3, within 3% for Re p ≤ 0.5 and within 9 % for Re p ≤ 1.0, where the single particle Reynolds number is defined in Equation (2.4). (2.4) (2.5) where R ′ is the force per unit projected area of the particle. Figure 2.1 Standard drag curve for motion of a sphere in a fluid Thus, for a sphere: (2.6) and, Stokes’ law, in terms of this drag coefficient, becomes: (2.7) At higher relative velocities, the inertia of the fluid begins to dominate (the fluid must accelerate out of the way of the particle). Analytical solution of the Navier–Stokes equations is not possible under these conditions. However, experiments give the relationship between the drag coefficient and the particle Reynolds number in the form of the so-called standard drag curve (Figure 2.1). Four regions are identified: the Stokes’ law region; the Newton’s law region in which drag coefficient is independent of Reynolds number; an intermediate region between the Stokes and Newton regions; and the boundary layer separation region...
eBook - ePubCoulson and Richardson's Chemical Engineering
Volume 2A: Particulate Systems and Particle Technology
- R. P. Chhabra, Basavaraj Gurappa(Authors)
- 2019(Publication Date)
- Butterworth-Heinemann(Publisher)
...The behaviour of a particle undergoing acceleration or retardation has been the subject of a very large number of investigations, which have been critically reviewed by Torobin and Gauvin 66 and others. 13 The results of different researchers are not consistent, although it is shown that the drag factor is often related, not only to the Reynolds number, but also to the number of particle diameters traversed by the particle since the initiation of the motion. A relatively simple approach to the problem, which gives results closely in accord with practical measurements, is to consider the mass of fluid which is effectively given the same acceleration as the particle, as discussed by Mironer. 67 This is only an approximation because elements of fluid at different distances from the particle will not all be subject to the same acceleration. For a spherical particle, this added or hydrodynamic mass is equal to the mass of fluid whose volume is equal to one half of that of the sphere. This can give rise to a very significant effect in the case of movement through a liquid, and can result in accelerations substantially less than those predicted when the added mass is neglected. For movement through gases, the contribution of the added mass term is generally negligible. Added mass is most important for the motion of gas bubbles in a liquid because, in that case, the surrounding liquid has a much greater density than the bubble. The total mass of particle and associated fluid is sometimes referred to as the virtual mass (m′). Thus : Virtual mass = Mass of particle + Added mass. For a sphere : m ′ = π 6 d 3 ρ s + π 12 d 3 ρ or : m ′ = π 6 d 3 ρ s 1 + ρ 2 ρ s = m 1 + ρ 2 ρ s (6.74) Considering the motion of a particle of mass m in the earth's gravitational field, at some time t, the particle will be moving at an angle α to the horizontal with a velocity u as shown in Fig. 6.7...
eBook - ePub- Alan Hendrickson(Author)
- 2012(Publication Date)
- Routledge(Publisher)
...4 The Friction Force, F friction DOI: 10.4324/9780080557540-4 Friction—Complex and Simplified Friction occurs between all matter in contact. Any combination of two materials, whether gaseous, liquid, or solid, will have unique friction characteristics dependent on many factors: the materials themselves, their surface finish, their speed relative to each other; the presence of any lubricant or impurities (dust and dirt); the direction of movement relative to any grain-like structure in a material; the pressure between the materials; temperature, and on and on. Because of all these factors, accurate mathematical models of frictional effects are extremely complex, and this is especially so for fluids. Fortunately, for the rough predictions of the loads imposed by friction on scenery movement, the complexity can be reduced considerably. Scenery movement speeds and “sail” area are usually low enough that air resistance can be considered nil. The flow of liquids, and of solids through liquids, is likewise beyond 99.9% of scenic situations (friction does affect oil flow in any hydraulic systems that we may use, but that topic is beyond the scope of this book). So for our needs here, friction will be considered only between solid materials, that can either slide against or roll over each other, in two states of motion — static, or not moving relative to each other, and dynamic, when movement does occur. The effect of friction on a move fits into the general formula for the maximum power needed to move an object as the friction force, F friction : P max = (F a c c e l + F f r i c t i o n + F l i f t i n g) v max Friction always opposes motion, and it never creates it...
