Phys. Chapter 08 - Beau Chene High School Home Page

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CHAPTER 8RotationalEquilibrium andDynamicsPHYSICS IN ACTIONOne of the most popular early bicycles wasthe penny-farthing, first introduced in 1870.The bicycle was named for the relative sizesof its two wheels compared to the relativesizes of the penny and the farthing, two Englishcoins. Early bicycles had no gears, justpedals attached directly to the wheel axle.This meant that the wheel turned once forevery revolution of the pedals.For the pennyfarthing,a gear was developed that allowedthe wheel to turn twice for every turn ofthe pedals. More stable bicycles with gearsand chains soon replaced the penny-farthing.• What makes a wheel difficult to rotate?• How much does a wheel accelerate for agiven applied force?CONCEPT REVIEWWork (Section 5-1)Energy (Section 5-2)Momentum (Section 6-1)Angular speed and acceleration(Section 7-1)Copyright © by Holt, Rinehart and Winston. All rights reserved.Rotational Equilibrium and Dynamics 277
8-1Torque8-1 SECTION OBJECTIVES• Recognize the differencebetween a point mass and anextended object.• Distinguish between torqueand force.• Calculate the magnitude of atorque on an object.• Identify the lever arm associatedwith a torque on anobject.THE MAGNITUDE OF A TORQUEYou have been chosen to judge a race involving three objects: a solid sphere, asolid cylinder, and a hollow cylinder. The spectators for the race demand that therace be fair, so you make sure that all of the objects have the same mass andradius and that they all start from rest. Then you let the three objects roll down along ramp. Is there a way to predict which one will win and which one will lose?If you really performed such a race (see the Quick Lab on the next page),you would discover that the sphere would come in first and that the hollowcylinder would come in last. This is a little surprising because in the absence offriction the acceleration due to gravity is the same for all objects near theEarth’s surface. Yet the acceleration of each of these objects is different.In earlier chapters, the motion of an object was described by assuming theobject was a point mass. This description, however, does not account for thedifferences in the motion of the objects in the race. This is because theseobjects are extended objects. An extended object is an object that has a definite,finite size and shape. Although anextended object can be treated as apoint mass to describe the motion ofits center of mass, a more sophisticatedmodel is required to describe its rotationalmotion.Figure 8-1In general, an extended object, such as one of these pins or this bowling ball, canexhibit rotational and translational motion.Rotational and translationalmotion can be separatedImagine that you roll a strike whilebowling. What happens when thebowling ball strikes the pins, as shownin Figure 8-1? The pins fly backward,spinning in the air. The complicatedmotion of each pin can be separatedinto a translational motion and a rotationalmotion, each of which can beanalyzed separately. For now, we willconcentrate on an object’s rotationalmotion. Then we will combine therotational motion of an object with itstranslational motion.278<strong>Chapter</strong> 8Copyright © by Holt, Rinehart and Winston. All rights reserved.
Page 1: Copyright © by Holt, Rinehart and
Page 5 and 6: •INTERACTIVEFigure 8-4In each exa
Page 7 and 8: PRACTICE 8ATorque1. Find the magnit
Page 9 and 10: MOMENT OF INERTIAmoment of inertiat
Page 11 and 12: inertia of a thin rod is larger if
Page 13 and 14: This value for the force in the wir
Page 15 and 16: •INTERACTIVE8-3Rotational dynamic
Page 17 and 18: MOMENTUMHave you ever swung a sledg
Page 19 and 20: Equate the initial and final angula
Page 21 and 22: SAMPLE PROBLEM 8EConservation of me
Page 23 and 24: 8-4Simple machines8-4 SECTION OBJEC
Page 25 and 26: Human ExtendersA cyborg, as any sci
Page 27 and 28: Earlier in this chapter, we discuss
Page 29 and 30: CHAPTER 8SummaryKEY TERMSangular mo
Page 31 and 32: CENTER OF MASS ANDROTATIONAL EQUILI
Page 33 and 34: 36. A 65 kg woman stands at the rim
Page 35 and 36: 60. A cylindrical 5.00 kg pulley wi
Page 37 and 38: 72. The efficiency of a pulley syst
Page 39 and 40: PROCEDUREInclined plane3. Set up th

Phys. Chapter 08 - Beau Chene High School Home Page

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