Lecture 21

# Lecture 21 - Lecture 21 pls-21.1 Torque and Static...

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Lecture 21 pls-21.1 Torque and Static Equilibrium Media: 1. Wooden tee with 1 kg mass 1. Torque Clicker question 1 . Torque is related to the ability of an external force to cause an object to rotate. The magnitude of the torque τ due to a particular force is given by l F = , where F is the magnitude of the force F r and l is the lever arm . The sign of the torque is positive if it tends to produce a CCW rotation, negative for a CW rotation. The lever arm is found with the following procedure. Draw a line in the direction of F r through the point on the object where the force acts. This line is known as the line of action . The lever arm l is the shortest distance from the pivot point to the line. (A) (B) (C) F F F l l l

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Lecture 21 pls-21.2 Notice that l is largest for case (A), so that the torque l F = τ is largest in this case. Which has the smallest torque? Demo: Wooden tee with 1 kg mass. Often there is an obvious point of rotation. Note, however, that sometimes you will calculate a lever arm and torque about a point that is not an obvious point of rotation. Example . As illustrated, a 20 m long beam at an angle of 35° with respect to the horizontal is being held up by a cable from above. (a) What is the lever arm associated with the force from the cable, assuming a pivot
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## This note was uploaded on 03/26/2012 for the course PHY 1020 taught by Professor Kodera during the Fall '11 term at University of Florida.

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Lecture 21 - Lecture 21 pls-21.1 Torque and Static...

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