PHY 121 Ch 10b Lecture

PHY 121 Ch 10b Lecture - Lecture 19 Tuesday, April 1 1 The...

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1 Lecture 19 Tuesday, April 1
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2 The rate of change of angular momentum of a particle equals. A. the net force acting on the particle. B. the net torque acting on the particle. C. the net work done by the forces acting on the particle. D. the rate of change of linear momentum times the distance to the center of rotation.
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3 For a rotating rigid body A. Angular momentum is always parallel to the angular velocity. B. Angular momentum is always perpendicular to the angular velocity. C. Angular momentum can make an arbitrary angle with the angular velocity. D. the angular velocity vector remains fixed in space.
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4 The assumptions made to demonstrate conservation of angular momentum are A. no net external torque. B. no net external torque and all internal action-reaction pairs along the same line. C. a cancellation between external and internal torques. D. no rotation of the object as a whole.
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5 If the polar ice caps were to completely melt due to global warming, the melted ice would redistribute itself over the Earth. This change would cause the length of the day A. to increase. B. to increase in the northern hemisphere and to decrease in the southern hemisphere. C. to decrease. D. to remain the same.
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6 Finding the missing analog We have found that all quantities defined for translational motion have a rotational analog: r !" v !# a !$ m ! I F 1 2 mv 2 ! 1 2 I # 2 What is the rotational analog of linear momentum ? ! p
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7 Angular momentum We now that ! F = d ! p dt Vector multiply times : ! r ! r ! ! F = ! r ! d ! p dt ! " = ! r ! d ! p dt = d dt ! r ! ! p [ ] = d ! L dt ! L = ! r ! ! p
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8 Example: Angular momentum of a planet ! L ! r ! v L = rp sin90 ! = rmv ! L = ! r ! ! p
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9 Conservation of linear momentum • The total linear momentum of a system of particles is conserved if the net external force is zero. • Internal forces do not affect linear momentum conservation because the contributions from the two members of the action- reaction pair cancel out: !
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PHY 121 Ch 10b Lecture - Lecture 19 Tuesday, April 1 1 The...

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