chapter8 - Chapter8 and RotationalDynamics Forcevs.Torque...

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    Chapter 8 Rotational Equilibrium  and Rotational Dynamics
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    Force vs. Torque Forces cause accelerations Torques cause angular accelerations Force and torque are related
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    Torque The door is free to rotate about an axis through O There are three factors that determine the  effectiveness of the force in opening the door: The  magnitude  of the force The  position  of the application of the force The  angle  at which the force is applied
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    Torque, cont Torque,  τ , is the tendency of a force to  rotate an object about some axis τ = r F   τ  is the torque Symbol is the Greek tau F is the force r is the length of the position vector SI unit is N . m
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    Direction of Torque Torque is a vector quantity The direction is perpendicular to the plane  determined by the position vector and the  force If the turning tendency of the force is  counterclockwise, the torque will be  positive If the turning tendency is clockwise, the  torque will be negative
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    Multiple Torques When two or more torques are acting on  an object, the torques are added As vectors If the net torque is zero, the object’s rate  of rotation doesn’t change
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    General Definition of Torque The applied force is not always  perpendicular to the position vector The component of the force  perpendicular  to the object will cause it  to rotate
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    General Definition of Torque,  cont When the force is  parallel to the  position vector, no  rotation occurs When the force is at  some angle, the  perpendicular  component causes  the rotation
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    General Definition of Torque,  final Taking the angle into account leads to a  more general definition of torque:   τ = r F sin  θ F is the force r is the position vector θ  is the angle between the force and the  position vector
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    Lever Arm The  lever arm , d, is the perpendicular distance from  the axis of rotation to a line drawn along the direction  of the force d = r sin  θ This also gives  τ  = rF sin  θ
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    Right Hand Rule Point the fingers in  the direction of the  position vector Curl the fingers  toward the force  vector The thumb points in  the direction of the  torque
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    Net Torque The net torque is the sum of all the  torques produced by all the forces Remember to account for the direction of  the tendency for rotation Counterclockwise torques are positive Clockwise torques are negative
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    Torque and Equilibrium First Condition of Equilibrium The net external force must be zero
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This note was uploaded on 07/19/2010 for the course PHYS 212 taught by Professor Sadler during the Spring '10 term at New Mexico.

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chapter8 - Chapter8 and RotationalDynamics Forcevs.Torque...

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