Chapter 6n00006757/physicslectures/Knight 2e/06_lect_outline/ja... · 1 © 2010 Pearson Education,...
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1 © 2010 Pearson Education, Inc. PowerPoint ® Lectures for College Physics: A Strategic Approach, Second Edition Chapter 6 Circular Motion, Orbits, and Gravity © 2010 Pearson Education, Inc. Slide 6-2 6 Circular Motion, Orbits, and Gravity © 2010 Pearson Education, Inc. Slide 6-3
Transcript of Chapter 6n00006757/physicslectures/Knight 2e/06_lect_outline/ja... · 1 © 2010 Pearson Education,...
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© 2010 Pearson Education, Inc.
PowerPoint® Lectures forCollege Physics: A Strategic Approach, Second Edition
Chapter 6
CircularMotion, Orbits,and Gravity
© 2010 Pearson Education, Inc. Slide 6-2
6 Circular Motion, Orbits, and Gravity
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Reading Quiz1. For uniform circular motion, the acceleration
A. is parallel to the velocity.B. is directed toward the center of the circle.C. is larger for a larger orbit at the same speed.D. is always due to gravity.E. is always negative.
Slide 6-6
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Answer1. For uniform circular motion, the acceleration
A. is parallel to the velocity.B. is directed toward the center of the circle.C. is larger for a larger orbit at the same speed.D. is always due to gravity.E. is always negative.
Slide 6-7
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Reading Quiz2. When a car turns a corner on a level road, which force provides
the necessary centripetal acceleration?
A. FrictionB. TensionC. Normal forceD. Air resistanceE. Gravity
Slide 6-8
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Answer2. When a car turns a corner on a level road, which force provides
the necessary centripetal acceleration?
A. FrictionB. TensionC. Normal forceD. Air resistanceE. Gravity
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3. Newton’s law of gravity describes the gravitationalforce between
A. the earth and the moon.B. a person and the earth.C. the earth and the sun.D. the sun and the planets.E. all of the above.
Reading Quiz
Slide 6-10
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Answer3. Newton’s law of gravity describes the gravitational
force between
A. the earth and the moon.B. a person and the earth.C. the earth and the sun.D. the sun and the planets.E. all of the above.
Slide 6-11
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Example ProblemsThe disk in a hard drive in a desktop computer rotates at7200 rpm. The disk has a diameter of 5.1 in (13 cm). What isthe angular speed of the disk?
Slide 6-12a
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Example ProblemsThe shaft of an elevator motor turns clockwise at 180 rpm for10 s, is at rest for 15 s, then turns counterclockwise at 240rpm for 12.5 s. What is the angular displacement of the shaftduring this motion?
Slide 6-12b
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Example ProblemsThe shaft of an elevator motor turns clockwise at 180 rpm for10 s, is at rest for 15 s, then turns counterclockwise at 240rpm for 12.5 s. What is the angular displacement of the shaftduring this motion? Draw angular position and angularvelocity graphs for the shaft’s motion.
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When a ball on the end of a string is swung in a vertical circle,the ball is accelerating because
A. the speed is changing.B. the direction is changing.C. the speed and the direction are changing.D. the ball is not accelerating.
Checking Understanding
Slide 6-13
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AnswerWhen a ball on the end of a string is swung in a vertical circle,the ball is accelerating because
A. the speed is changing.B. the direction is changing.C. the speed and the direction are changing.D. the ball is not accelerating.
Slide 6-14
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When a ball on the end of a string is swung in a vertical circle:What is the direction of the acceleration of the ball?
A. Tangent to the circle, in the direction of the ball’smotion
B. Toward the center of the circle
Checking Understanding
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AnswerWhen a ball on the end of a string is swung in a vertical circle:What is the direction of the acceleration of the ball?
A. Tangent to the circle, in the direction of the ball’smotion
B. Toward the center of the circle
Slide 6-16
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For the ball on the end of a string moving in a vertical circle:What force is producing the centripetal acceleration of the ball?
A. gravityB. air resistanceC. normal forceD. tension in the string
Checking Understanding:Circular Motion Dynamics
Slide 6-17
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Answer
For the ball on the end of a string moving in a vertical circle:What force is producing the centripetal acceleration of the ball?
A. gravityB. air resistanceC. normal forceD. tension in the string
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For the ball on the end of a string moving in a vertical circle:What is the direction of the net force on the ball?
A. tangent to the circleB. toward the center of the circleC. there is no net force
Checking Understanding:Circular Motion Dynamics
Slide 6-19
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Answer
For the ball on the end of a string moving in a vertical circle:What is the direction of the net force on the ball?
A. tangent to the circleB. toward the center of the circleC. there is no net force
Slide 6-20
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When the ball reaches the break in the circle, which path will itfollow?
Checking Understanding:Circular Motion Dynamics
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Answer
When the ball reaches the break in the circle, which path will itfollow?
C.
Slide 6-22
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Uniform Circular Motion
Slide 6-23
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Forces in Circular Motion
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Example ProblemThe hard drive disk in the earlier example rotates at 7200 rpm.The disk has a diameter of 5.1 in (13 cm). What is the speed ofa point 6.0 cm from the center axle? What is the acceleration ofthis point on the disk?
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Solving Problems
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Solving Problems
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Example ProblemA level curve on acountry road has aradius of 150 m. Whatis the maximum speedat which this curve canbe safely negotiated ona rainy day when thecoefficient of frictionbetween the tires on acar and the road is0.40?
Slide 6-28
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Example ProblemA level curve on acountry road has aradius of 150 m. Whatis the maximum speedat which this curve canbe safely negotiated ona rainy day when thecoefficient of frictionbetween the tires on acar and the road is0.40?
Slide 6-28
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In the hammer throw, anathlete spins a heavy massin a circle at the end of achain, then lets go of thechain. For male athletes,the “hammer” is a mass of7.3 kg at the end of a 1.2 mchain.
Example Problem
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A world-classthrower can getthe hammer up toa speed of 29m/s. If an athleteswings the massin a horizontalcircle centered onthe handle heuses to hold thechain, what is thetension in thechain?
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A car of mass 1500 kg goes overa hill at a speed of 20 m/s. Theshape of the hill is approximatelycircular, with a radius of 60 m, asin the figure at right. When the caris at the highest point of the hill,
a. What is the force of gravityon the car?
b. What is the normal force ofthe road on the car at thispoint?
Example Problem: Driving Over A Rise
Slide 6-30
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Maximum Walking Speed
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Example Problem: Loop-the-LoopA roller coaster car goes through a vertical loop at a constantspeed. For positions A to E, rank order the:
• centripetal acceleration
• normal force
• apparent weight
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Example Problem: Over the TopA handful of professional skaters have taken a skateboardthrough an inverted loop in a full pipe. For a typical pipe withdiameter 14 ft, what is the minimum speed the skater must haveat the very top of the loop?
Slide 6-33
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Example Problem: Orbital MotionPhobos is one of two small moons that orbit Mars. Phobos is avery small moon, and has correspondingly small gravity—it varies,but a typical value is about 6 mm/s2. Phobos isn’t quite round, but ithas an average radius of about 11 km. What would be the orbitalspeed around Phobos, assuming it was round with gravity andradius as noted?
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The Force of Gravity
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A typical bowling ball is spherical, weighs 16 pounds, and has adiameter of 8.5 in. Suppose two bowling balls are right next toeach other in the rack. What is the gravitational force betweenthe two—magnitude and direction?
Example Problem
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What is the magnitude and direction of the force of gravity ona 60 kg person?
Example Problem
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Checking Understanding:Gravity on Other WorldsA 60 kg person stands on each of the following planets. Rankorder her weight on the three bodies, from highest to lowest.
A. A > B > CB. B > A > CC. B > C > AD. C > B > AE. C > A > B
Slide 6-38
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AnswerA 60 kg person stands on each of the following planets. Rankorder her weight on the three bodies, from highest to lowest.
A. A > B > CB. B > A > CC. B > C > AD. C > B > AE. C > A > B
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A spacecraft is orbiting the moon in an orbit very close to thesurface—possible because of the moon’s lack of atmosphere.What is the craft’s speed? The period of its orbit?
Example Problems: Gravity and Orbits
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Phobos is the closer of Mars’ two small moons, orbiting at 9400km from the center of Mars, a planet of mass6.4 1023 kg. What is Phobos’ orbital period? How does thiscompare to the length of the Martian day, which is just shy of 25hours?
Example Problems: Gravity and Orbits
Slide 6-40b
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Summary
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Summary
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Additional QuestionsA satellite orbits the earth. A Space Shuttle crew is sent to boost thesatellite into a higher orbit. Which of these quantities increases?
A. SpeedB. Angular speedC. PeriodD. Centripetal accelerationE. Gravitational force of the earth
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AnswerA satellite orbits the earth. A Space Shuttle crew is sent to boost thesatellite into a higher orbit. Which of these quantities increases?
A. SpeedB. Angular speedC. PeriodD. Centripetal accelerationE. Gravitational force of the earth
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A coin sits on a rotatingturntable.
1. At the time shown in thefigure, which arrow gives thedirection of the coin’svelocity?
Additional Questions
Slide 6-45
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AnswerA coin sits on a rotatingturntable.
1. At the time shown in thefigure, which arrow gives thedirection of the coin’svelocity?
A
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A coin sits on a rotatingturntable.
2. At the time shown in thefigure, which arrow gives thedirection of the frictionalforce on the coin?
Additional Questions
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AnswerA coin sits on a rotatingturntable.
2. At the time shown in thefigure, which arrow gives thedirection of the frictionalforce on the coin? D
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A coin sits on a rotatingturntable.
3. At the instant shown,suppose the frictional forcedisappeared. In whatdirection would the coinmove?
Additional Questions
Slide 6-49
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Answer
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A coin sits on a rotatingturntable.
3. At the instant shown,suppose the frictional forcedisappeared. In whatdirection would the coinmove?
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Additional Example ProblemsAt Talladega, a NASCAR track, the turns have a 370 m radius andare banked at 33°. At what speed can a car go around this cornerwith no assistance from friction?
Slide 6-51
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Additional Example ProblemsThe Globe of Death isa spherical cage inwhich motorcyclistsride in circular pathsat high speeds. Oneoutfit claims thatriders achieve aspeed of 60 mphin a 16 ft diametersphere. What wouldbe the period for thismotion? What wouldbe the apparentweight of a 60 kg riderat the bottom of thesphere? Given thesetwo pieces ofinformation, does thishigh speed in thissmall sphere seempossible?
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