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Unformatted text preview: Chapter 8 Rotational Equilibrium and Rotational Dynamics • shortened day by 1.8 microseconds • Sumatra quake shortened day by 6.8 microseconds • Why? • via: http://www.csmonitor.com/ Science/2011/0314/Japanearthquake acceleratedEarthsrotationstudyfnds “Japan earthquake accelerated Earth's rotation, study fnds” • Forces cause accelerations • Torques cause angular accelerations • Force and torque are related Force vs. Torque 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 Torque, cont ! Torque, τ , is the tendency of a force to rotate an object about some axis ! τ = r F sin θ ! τ is the torque ! F is the force ! symbol is the Greek tau ! r is the length of the position vector ! SI unit is N . m ! 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 Direction of Torque 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 SVCh08P03 Calculate the net torque (magnitude and direction) on the beam about (a) an axis through O perpendicular to the page and (b) an axis through C perpendicular to the page. Are they diferent? General Defnition 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 General Defnition oF Torque, cont !...
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 Fall '08
 staff
 Force, lever arm

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