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Moments and Torque

living with the lab. Moments and Torque. Torque , also called moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist. d 1. d 2. F 1. F 2. living with the lab.

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Moments and Torque

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  1. living with the lab Moments and Torque Torque, also called moment or moment of force, is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist. d1 d2 F1 F2

  2. living with the lab Definition of a Moment d acme tire F A UNITS: The moment or torque of the force F about point A is a measure of the tendency of F to produce rotation about point A.

  3. living with the lab Consider the moment of F about point A for the cases below. d F A line of action d F line of action A line of action line of action d A A F F

  4. living with the lab Class Example • The semicircular segment pivots about point A. • What is the moment of F1 about A? • What is the moment of F2 about A? 1 in 1 in 1 ft 1 in 1 in a. 8 in A 6 in b. F1 = 100 lbs F2 = 80 lbs

  5. living with the lab Class Example Find the moment of F about point A. d1 = 2m A + d2 = 3m 55° F = 100N

  6. living with the lab What is the difference between a moment and a torque? • The words moment and torque are often used interchangeably. A moment and a torque are physically the same thing; they are both a measure of the tendency of a force or set of forces to produce rotation. • Moment is a more general term than torque. A torque is a special application of a moment and generally refers to the tendency to produce rotation about an axle. Typical usage of these words can vary by discipline and location. • A gearmotor can output a peak torque of 6N-m (physical rotation occurs about the motor shaft). • The weight of a child who climbs out on the branch of a tree will induce a moment on the limb; the moment will be maximum at the base of the branch.

  7. living with the lab Class Problem • Uncle Fred who weighs 200 lbs. is riding a Ferris wheel at the county fair along with his 80 lb. son, Freddie. The Ferris wheel has a diameter of 30 feet. • What moment will Uncle Fred exert about the center of rotation (point A) when q = 45° if he is the only one riding? Will this moment act clockwise (CW) or counter clockwise (CCW)? • What moment will Freddie exert about the center of rotation (point A) when q= 45° if he is the only one riding (his angle is actually 45° + 90° = 135°)? Will this moment act CW or CCW? • What is the net moment about point A when q= 45° and both are riding? Assume that a CW moment is positive and a CCW moment is negative. Is the net moment CW or CCW? • Derive an equation for the moment about point A as a function of qwhen both people are riding. • Using Mathcad, plot the net moment for q= 0° to q= 360°. • Assumptions: • Ignore dynamic effects. • Assume the weights of Uncle Fred and Freddieare centered at the pin where their chairs are connected to the circular structure.

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