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Torque

Physics 7C lecture 12. Torque. Thursday November 7, 8:00 AM – 9:20 AM Engineering Hall 1200. Loosen a bolt. Which of the three equal-magnitude forces in the figure is most likely to loosen the bolt?. Loosen a bolt.

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Torque

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  1. Physics 7C lecture 12 • Torque Thursday November 7, 8:00 AM – 9:20 AM Engineering Hall 1200

  2. Loosen a bolt • Which of the three equal-magnitude forces in the figure is most likely to loosen the bolt?

  3. Loosen a bolt • Which of the three equal-magnitude forces in the figure is most likely to loosen the bolt? torque τ is proportional to both force and distance.

  4. Torque has its sign • The line of action of a force is the line along which the force vector lies. • The lever arm (or moment arm) for a force is the perpendicular distance from O to the line of action of the force (see figure). • The torque of a force with respect to O is the product of the force and its lever arm.

  5. Torque has its sign • torque τ = r X F

  6. Q10.1 F1 F3 The four forces shown all have the same magnitude: F1 = F2 = F3 = F4. Which force produces the greatesttorque about the point O (marked by the blue dot)? O F2 F4 A. F1 B. F2 C. F3 D. F4 E. not enough information given to decide

  7. A10.1 F1 F3 The four forces shown all have the same magnitude: F1 = F2 = F3 = F4. Which force produces the greatesttorque about the point O (marked by the blue dot)? O F2 F4 A. F1 B. F2 C. F3 D. F4 E. not enough information given to decide

  8. Calculate torque • torque τ = r X F • F = Fxi + Fy j • r = x i + y j

  9. Q10.4 A force acts on an object at a point located at the position What is the torque that this force applies about the origin? A. zero B. C. D. E.

  10. A10.4 A force acts on an object at a point located at the position What is the torque that this force applies about the origin? A. zero B. C. D. E.

  11. Torque as a vector • Torque can be expressed as a vector using the vector product. • how to find the direction of torque using a right hand rule.

  12. Q10.2 F1 F3 Which of the four forces shown here produces a torque about O that is directed out of the plane of the drawing? O F2 F4 A. F1 B. F2 C. F3 D. F4 E. more than one of these

  13. A10.2 F1 F3 Which of the four forces shown here produces a torque about O that is directed out of the plane of the drawing? O F2 F4 A. F1 B. F2 C. F3 D. F4 E. more than one of these

  14. Applying a torque • Calculate the torque

  15. Applying a torque • Calculate the torque

  16. Q10.3 A plumber pushes straight down on the end of a long wrench as shown. What is the magnitude of the torque he applies about the pipe at lower right? A. (0.80 m)(900 N)sin 19° B. (0.80 m)(900 N)cos 19° C. (0.80 m)(900 N)tan 19° D. none of the above

  17. A10.3 A plumber pushes straight down on the end of a long wrench as shown. What is the magnitude of the torque he applies about the pipe at lower right? A. (0.80 m)(900 N)sin 19° B. (0.80 m)(900 N)cos 19° C. (0.80 m)(900 N)tan 19° D. none of the above

  18. Torque and angular acceleration for a rigid body • The rotational analog of Newton’s second law for a rigid body is z =Iz.

  19. Torque and angular acceleration for a rigid body • Calculate angular accelaration

  20. Torque and angular acceleration for a rigid body • Calculate angular acceleration

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