Lecture 18, Structure of Spiral Galaxies
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Rotational Motion (The Dynamics of a Rigid Body)
University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Robert Katz Publications Research Papers in Physics and Astronomy 1-1958 Physics, Chapter 11: Rotational Motion (The Dynamics of a Rigid Body) Henry Semat City College of New York Robert Katz University of Nebraska-Lincoln, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/physicskatz Part of the Physics Commons Semat, Henry and Katz, Robert, "Physics, Chapter 11: Rotational Motion (The Dynamics of a Rigid Body)" (1958). Robert Katz Publications. 141. https://digitalcommons.unl.edu/physicskatz/141 This Article is brought to you for free and open access by the Research Papers in Physics and Astronomy at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Robert Katz Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. 11 Rotational Motion (The Dynamics of a Rigid Body) 11-1 Motion about a Fixed Axis The motion of the flywheel of an engine and of a pulley on its axle are examples of an important type of motion of a rigid body, that of the motion of rotation about a fixed axis. Consider the motion of a uniform disk rotat ing about a fixed axis passing through its center of gravity C perpendicular to the face of the disk, as shown in Figure 11-1. The motion of this disk may be de scribed in terms of the motions of each of its individual particles, but a better way to describe the motion is in terms of the angle through which the disk rotates. -
Basic Galactic Dynamics
5 Basic galactic dynamics 5.1 Basic laws govern galaxy structure The basic force on galaxy scale is gravitational • Why? The other long-range force is electro-magnetic force due to electric • charges: positive and negative charges are difficult to separate on galaxy scales. 5.1.1 Gravitational forces Gravitational force on a point mass M1 located at x1 from a point mass M2 located at x2 is GM M (x x ) F = 1 2 1 − 2 . 1 − x x 3 | 1 − 2| Note that force F1 and positions, x1 and x2 are vectors. Note also F2 = F1 consistent with Newton’s Third Law. Consider a stellar− system of N stars. The gravitational force on ith star is the sum of the force due to all other stars N GM M (x x ) F i j i j i = −3 . − xi xj Xj=6 i | − | The equation of motion of the ith star under mutual gravitational force is given by Newton’s second law, dv F = m a = m i i i i i dt and so N dvi GMj(xi xj) = − 3 . dt xi xj Xj=6 i | − | 5.1.2 Energy conservation Assuming M2 is fixed at the origin, and M1 on the x-axis at a distance x1 from the origin, we have m1dv1 GM1M2 = 2 dt − x1 1 2 Using 2 dv1 dx1 dv1 dv1 1 dv1 = = v1 = dt dt dx1 dx1 2 dx1 we have 2 1 dv1 GM1M2 m1 = 2 , 2 dx1 − x1 which can be integrated to give 1 2 GM1M2 m1v1 = E , 2 − x1 The first term on the lhs is the kinetic energy • The second term on the lhs is the potential energy • E is the total energy and is conserved • 5.1.3 Gravitational potential The potential energy of M1 in the potential of M2 is M Φ , − 1 × 2 where GM2 Φ2 = − x1 is the potential of M2 at a distance x1 from it. -
Australia Telescope National Facility Annual Report 2002
Australia Telescope National Facility Australia Telescope National Facility Annual Report 2002 Annual Report 2002 © Australia Telescope National CSIRO Australia Telescope National Facility Annual Report 2002 Facility ISSN 1038-9554 PO Box 76 Epping NSW 1710 This is the report of the Steering Australia Committee of the CSIRO Tel: +61 2 9372 4100 Australia Telescope National Facility for Fax: +61 2 9372 4310 the calendar year 2002. Parkes Observatory PO Box 276 Editor: Dr Jessica Chapman, Parkes NSW 2870 Australia Telescope National Facility Design and typesetting: Vicki Drazenovic, Australia Australia Telescope National Facility Tel: +61 2 6861 1700 Fax: +61 2 6861 1730 Printed and bound by Pirion Printers Pty Paul Wild Observatory Narrabri Cover image: Warm atomic hydrogen gas is a Locked Bag 194 major constituent of our Galaxy, but it is peppered Narrabri NSW 2390 with holes. This image, made with the Australia Australia Telescope Compact Array and the Parkes radio telescope, shows a structure called Tel: +61 2 6790 4000 GSH 277+00+36 that has a void in the atomic Fax: +61 2 6790 4090 hydrogen more than 2,000 light years across. It lies 21,000 light years from the Sun on the edge of the [email protected] Sagittarius-Carina spiral arm in the outer Milky Way. www.atnf.csiro.au The void was probably formed by winds and supernova explosions from about 300 massive stars over the course of several million years. It eventually grew so large that it broke out of the disk of the Galaxy, forming a “chimney”. GSH 277+00+36 is one of only a handful of chimneys known in the Milky Way and the only one known to have exploded out of both sides of the Galactic plane. -
Center of Mass, Torque and Rotational Inertia
Center of Mass, Torque and Rotational Inertia Objectives 1. Define center of mass, center of gravity, torque, rotational inertia 2. Give examples of center of gravity 3. Explain how center of mass affects rotation and toppling 4. Write the equations for torque and rotational inertia 5. Explain how to change torque and rotational inertia Center of Mass/Gravity • COM – point which is at the center of the objects mass – Middle of meter stick – Center of a ball – Middle of a donut • Donuts are yummy • COG – center of object’s weight distribution – Usually the same point as center of mass Rotation and Center of Mass • Objects rotate around their center of mass – Wobbling baseball bat tossed through the air • They also balance there – Balancing a broom on your finger • Things topple over when their center of gravity is not above the base – Leaning Tower of Pisa Torque • Force that causes rotation • Equation τ = Fr τ = torque (in Nm) F = force (in N) r = arm radius (in m) • How do you increase torque – More force – Longer radius Rotational Inertia • Resistance of an object to a change in its rotational motion • Controlled by mass distribution and location of axis • Equation I = mr2 I = rotational inertia (in kgm2) m = mass (in kg) r = radius (in m) • How do you increase rotational inertia? – Even mass distribution Angular Momentum • Measure how difficult it is to start or stop a rotating object • Equations L = Iω = mvtr • It is easier to balance on a moving bicycle • Precession – Torque applied to a spinning wheel changes the direction of its angular momentum – The wheel rotates about the axis instead of toppling over Satellite Motion John Glenn 6 min • Satellites “fall around” the object they orbit • The tangential speed must be exact to match the curvature of the surface of the planet – On earth things fall 4.9 m in one second – Earth “falls” 4.9 m every 8000 m horizontally – Therefore a satellite must have a tangential speed of 8000 m/s to keep from hitting the ground – Rockets are launched vertically and rolled to horizontal during their flights Sputnik-30 sec . -
7.5 X 11.5.Threelines.P65
Cambridge University Press 978-0-521-19267-5 - Observing and Cataloguing Nebulae and Star Clusters: From Herschel to Dreyer’s New General Catalogue Wolfgang Steinicke Index More information Name index The dates of birth and death, if available, for all 545 people (astronomers, telescope makers etc.) listed here are given. The data are mainly taken from the standard work Biographischer Index der Astronomie (Dick, Brüggenthies 2005). Some information has been added by the author (this especially concerns living twentieth-century astronomers). Members of the families of Dreyer, Lord Rosse and other astronomers (as mentioned in the text) are not listed. For obituaries see the references; compare also the compilations presented by Newcomb–Engelmann (Kempf 1911), Mädler (1873), Bode (1813) and Rudolf Wolf (1890). Markings: bold = portrait; underline = short biography. Abbe, Cleveland (1838–1916), 222–23, As-Sufi, Abd-al-Rahman (903–986), 164, 183, 229, 256, 271, 295, 338–42, 466 15–16, 167, 441–42, 446, 449–50, 455, 344, 346, 348, 360, 364, 367, 369, 393, Abell, George Ogden (1927–1983), 47, 475, 516 395, 395, 396–404, 406, 410, 415, 248 Austin, Edward P. (1843–1906), 6, 82, 423–24, 436, 441, 446, 448, 450, 455, Abbott, Francis Preserved (1799–1883), 335, 337, 446, 450 458–59, 461–63, 470, 477, 481, 483, 517–19 Auwers, Georg Friedrich Julius Arthur v. 505–11, 513–14, 517, 520, 526, 533, Abney, William (1843–1920), 360 (1838–1915), 7, 10, 12, 14–15, 26–27, 540–42, 548–61 Adams, John Couch (1819–1892), 122, 47, 50–51, 61, 65, 68–69, 88, 92–93, -
Chapter 8: Rotational Motion
TODAY: Start Chapter 8 on Rotation Chapter 8: Rotational Motion Linear speed: distance traveled per unit of time. In rotational motion we have linear speed: depends where we (or an object) is located in the circle. If you ride near the outside of a merry-go-round, do you go faster or slower than if you ride near the middle? It depends on whether “faster” means -a faster linear speed (= speed), ie more distance covered per second, Or - a faster rotational speed (=angular speed, ω), i.e. more rotations or revolutions per second. • Linear speed of a rotating object is greater on the outside, further from the axis (center) Perimeter of a circle=2r •Rotational speed is the same for any point on the object – all parts make the same # of rotations in the same time interval. More on rotational vs tangential speed For motion in a circle, linear speed is often called tangential speed – The faster the ω, the faster the v in the same way v ~ ω. directly proportional to − ω doesn’t depend on where you are on the circle, but v does: v ~ r He’s got twice the linear speed than this guy. Same RPM (ω) for all these people, but different tangential speeds. Clicker Question A carnival has a Ferris wheel where the seats are located halfway between the center and outside rim. Compared with a Ferris wheel with seats on the outside rim, your angular speed while riding on this Ferris wheel would be A) more and your tangential speed less. B) the same and your tangential speed less. -
Galactic Mass Distribution Without Dark Matter Or Modified Newtonian
1 astro-ph/0309762 v2, revised 1 Mar 2007 Galactic mass distribution without dark matter or modified Newtonian mechanics Kenneth F Nicholson, retired engineer key words: galaxies, rotation, mass distribution, dark matter Abstract Given the dimensions (including thickness) of a galaxy and its rotation profile, a method is shown that finds the mass and density distribution in the defined envelope that will cause that rotation profile with near-exact speed matches. Newton's law is unchanged. Surface-light intensity and dark matter are not needed. Results are presented in dimensionless plots allowing easy comparisons of galaxies. As compared with the previous version of this paper the methods are the same, but some data are presented in better dimensionless parameters. Also the part on thickness representation is simplified and extended, the contents are rearranged to have a logical buildup in the problem development, and more examples are added. 1. Introduction Methods used for finding mass distribution of a galaxy from rotation speeds have been mostly those using dark-matter spherical shells to make up the mass needed beyond the assumed loading used (as done by van Albada et al, 1985), or those that modify Newton's law in a way to approximately match measured data (for example MOND, Milgrom, 1983). However the use of the dark-matter spheres is not a correct application of Newton's law, and (excluding relativistic effects) modifications to Newton's law have not been justified. In the applications of dark-matter spherical shells it is assumed that all galaxies are in two parts, a thin disk with an exponential SMD loading (a correct solution for rotation speeds by Freeman, 1970) and a series of spherical shells centered on the galaxy center. -
Multiple Integrals
Chapter 11 Multiple Integrals 11.1 Double Riemann Sums and Double Integrals over Rectangles Motivating Questions In this section, we strive to understand the ideas generated by the following important questions: What is a double Riemann sum? • How is the double integral of a continuous function f = f(x; y) defined? • What are two things the double integral of a function can tell us? • Introduction In single-variable calculus, recall that we approximated the area under the graph of a positive function f on an interval [a; b] by adding areas of rectangles whose heights are determined by the curve. The general process involved subdividing the interval [a; b] into smaller subintervals, constructing rectangles on each of these smaller intervals to approximate the region under the curve on that subinterval, then summing the areas of these rectangles to approximate the area under the curve. We will extend this process in this section to its three-dimensional analogs, double Riemann sums and double integrals over rectangles. Preview Activity 11.1. In this activity we introduce the concept of a double Riemann sum. (a) Review the concept of the Riemann sum from single-variable calculus. Then, explain how R b we define the definite integral a f(x) dx of a continuous function of a single variable x on an interval [a; b]. Include a sketch of a continuous function on an interval [a; b] with appropriate labeling in order to illustrate your definition. (b) In our upcoming study of integral calculus for multivariable functions, we will first extend 181 182 11.1. -
Dirac Function and Its Applications in Solving Some Problems in Mathematics
Dirac function and its applications in solving some problems in mathematics Hisham Rehman Mohammed Department of Mathematics Collage of computer science and Mathematics University of Al- Qadisiyia Diwaniya-Iraq E-mail:hisham [email protected] Abstract The paper presents various ways of defining and introducing Dirac delta function, its application in solving some problems and show the possibility of using delta- function in mathematics and physics. Introduction The development of science requires for its theoretical basis more and more "high mathematics", one of the achievements which are generalized functions, in particular the Dirac function. The theory of generalized functions is relevant in physics and mathematics, as have of remarkable properties that extend the classical mathematical analysis extends the range of tasks and, moreover, leads to significant simplifications in the calculations, automating basic operations. The objectives of this work: 1) study the concept of Dirac function; 2) to consider the physical and mathematical approaches to its definition; 3) show the application to the determination of derivatives of discontinuous functions. 1.1. Basic concepts. In various issues of mathematical analysis, the term "function" has to understand, with varying degrees of generality. Sometimes considered continuous but not differentiable functions, other issues have to assume that we are talking about functions, differentiable once or several times, etc. However, in some cases, the classical notion of function, even interpreted in the broadest sense,that is as an 1 arbitrary rule, which relates each value of x in the domain of this function, a number of y = f (x), is insufficient. That's an important example: using the apparatus of mathematical analysis to some problems, we are faced with a situation in which certain operations analysis are impractical, for example, a function that has no derivative (in some points or even everywhere), it is impossible to differentiate if derivatives are understood as an elementary function. -
Dynamical Aspects of Inextensible Chains
NSF-KITP-11-092 Dynamical aspects of inextensible chains Franco Ferrari ∗1,2 and Maciej Pyrka †3 1Institute of Physics and CASA*, University of Szczecin,, ul. Wielkopolska 15, 70-451 Szczecin, Poland 2Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106, USA 3Department of Physics and Biophysics, Medical University of Gda´nsk, ul. D¸ebinki 1, 80-211 Gda´nsk August 26, 2018 Abstract In the present work the dynamics of a continuous inextensible chain is studied. The chain is regarded as a system of small particles subjected to constraints on their reciprocal distances. It is proposed a treatment of systems of this kind based on a set Langevin equations in which the noise is characterized by a non-gaussian probability distribution. The method is explained in the case of a freely hinged chain. In particular, the generating functional of the correlation functions of the relevant degrees of freedom which describe the conformations of this chain is derived. It is shown that in the continuous limit this generating functional coincides with a model of an inextensible chain previously discussed by one of the authors of this work. Next, the approach developed here is applied to a inextensible chain, called the freely jointed bar chain, in which the basic units are small extended objects. The generating functional of the freely jointed bar chain is constructed. It is shown that it differs profoundly from that of the freely hinged chain. Despite the differences, it is verified that in the continuous limit both generating functionals coincide as it is expected. -
Chapter 5 Rotation Curves
Chapter 5 Rotation Curves 5.1 Circular Velocities and Rotation Curves The circular velocity vcirc is the velocity that a star in a galaxy must have to maintain a circular orbit at a specified distance from the centre, on the assumption that the gravitational potential is symmetric about the centre of the orbit. In the case of the disc of a spiral galaxy (which has an axisymmetric potential), the circular velocity is the orbital velocity of a star moving in a circular path in the plane of the disc. If 2 the absolute value of the acceleration is g, for circular velocity we have g = vcirc=R where R is the radius of the orbit (with R a constant for the circular orbit). Therefore, 2 @Φ=@R = vcirc=R, assuming symmetry. The rotation curve is the function vcirc(R) for a galaxy. If vcirc(R) can be measured over a range of R, it will provide very important information about the gravitational potential. This in turn gives fundamental information about the mass distribution in the galaxy, including dark matter. We can go further in cases of spherical symmetry. Spherical symmetry means that the gravitational acceleration at a distance R from the centre of the galaxy is simply GM(R)=R2, where M(R) is the mass interior to the radius R. In this case, 2 vcirc GM(R) GM(R) = 2 and therefore, vcirc = : (5.1) R R r R If we can assume spherical symmetry, we can estimate the mass inside a radial distance R by inverting Equation 5.1 to give v2 R M(R) = circ ; (5.2) G and can do so as a function of radius. -
190 Index of Names
Index of names Ancora Leonis 389 NGC 3664, Arp 005 Andriscus Centauri 879 IC 3290 Anemodes Ceti 85 NGC 0864 Name CMG Identification Angelica Canum Venaticorum 659 NGC 5377 Accola Leonis 367 NGC 3489 Angulatus Ursae Majoris 247 NGC 2654 Acer Leonis 411 NGC 3832 Angulosus Virginis 450 NGC 4123, Mrk 1466 Acritobrachius Camelopardalis 833 IC 0356, Arp 213 Angusticlavia Ceti 102 NGC 1032 Actenista Apodis 891 IC 4633 Anomalus Piscis 804 NGC 7603, Arp 092, Mrk 0530 Actuosus Arietis 95 NGC 0972 Ansatus Antliae 303 NGC 3084 Aculeatus Canum Venaticorum 460 NGC 4183 Antarctica Mensae 865 IC 2051 Aculeus Piscium 9 NGC 0100 Antenna Australis Corvi 437 NGC 4039, Caldwell 61, Antennae, Arp 244 Acutifolium Canum Venaticorum 650 NGC 5297 Antenna Borealis Corvi 436 NGC 4038, Caldwell 60, Antennae, Arp 244 Adelus Ursae Majoris 668 NGC 5473 Anthemodes Cassiopeiae 34 NGC 0278 Adversus Comae Berenices 484 NGC 4298 Anticampe Centauri 550 NGC 4622 Aeluropus Lyncis 231 NGC 2445, Arp 143 Antirrhopus Virginis 532 NGC 4550 Aeola Canum Venaticorum 469 NGC 4220 Anulifera Carinae 226 NGC 2381 Aequanimus Draconis 705 NGC 5905 Anulus Grahamianus Volantis 955 ESO 034-IG011, AM0644-741, Graham's Ring Aequilibrata Eridani 122 NGC 1172 Aphenges Virginis 654 NGC 5334, IC 4338 Affinis Canum Venaticorum 449 NGC 4111 Apostrophus Fornac 159 NGC 1406 Agiton Aquarii 812 NGC 7721 Aquilops Gruis 911 IC 5267 Aglaea Comae Berenices 489 NGC 4314 Araneosus Camelopardalis 223 NGC 2336 Agrius Virginis 975 MCG -01-30-033, Arp 248, Wild's Triplet Aratrum Leonis 323 NGC 3239, Arp 263 Ahenea