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Engr 240 – Week 12

Engr 240 – Week 12. Chapter 16. Kinetics of Rigid Bodies: Forces And Accelerations. and. The system of the external forces is equivalent to the system consisting of the vector attached at G and the couple of moment. Equations of Motion for a Rigid Body.

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Engr 240 – Week 12

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  1. Engr 240 – Week 12 Chapter 16. Kinetics of Rigid Bodies: Forces And Accelerations

  2. and The system of the external forces is equivalent to the system consisting of the vector attached at G and the couple of moment . Equations of Motion for a Rigid Body .

  3. Consider a rigid slab made up of a large number of particles of mass . - position vector of ith particle where: - linear momentum of ith particle But: which has the same direction as Therefore and of magnitude . Centroidal moment of inertia to the slab. Differentiating both sides with respect to time: Angular Momentum In Plane Motion The angular momentum about the centroidal frame Gx’y’ is Hence:

  4. The external forces acting on a rigid body is equivalent to the system consisting of a vector attached to the center of mass G, and a couple of moment . and D’ALEMBERT’S PRINCIPLE For a rigid body in plane motion: and , . The two vector equations: three independent scalar equations:

  5. Translation: Centroidal Rotation: NOTE: Before applying D’Alembert’s principle, it may be necessary to analyze kinematics of motion to reduce the number of unknown kinematic variables.

  6. Example 1. A pulley weighing 12 lb and having a radius of gyration of 8 in is connected to two blocks as shown. Assuming no axle friction, determine the angular acceleration of the pulley and the acceleration of each block.

  7. Example 2. The spool has a mass of 8 kg and a radius of gyration of kG=0.35 m about its center. If cords of negligible mass are wrapped around its inner hub and outer rim as shown, determine its angular acceleration.

  8. Example 3. A slender bar AB weighs 60 lbs and moves in the vertical plane, with its ends constrained to follow the smooth horizontal and vertical guides. If the 30-lb force is applied at A with the bar initially at rest in the position shown for which =30, calculate the resulting angular acceleration of the bar and the forces on the small end rollers at A and B.

  9. Rolling Motion: Rolling Without Sliding

  10. Rolling With Sliding:

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