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Unformatted text preview: 2D Rigid Body Rotational Kinetics Angular momentum Angular momentum L : For a point mass (particle): L = m A = m r sin = m r A : perpendicular distance from O (pivot) to the line of G r : distance from O (pivot) to the point mass : angle between r and : velocity component perpendicular to r For a rigid body in pure rotation: L = I about pivot point O Direction of L : CW or CCW for 2D rotation Newtons 2nd law for 2D rigid body pure rotation : dL dt = Conservation of angular momentum = 0 L i = L f or L 1 = L 2 Note: Collision involving a pivoted rigid body: Conservation of momentum is NOT valid. Only conservation of angular momentum is applicable. Example 1. Two identical small spheres, each with mass 0.2 Kg, are mounted on a 0.8 Kg slender rod. The 0.9 m long slender rod pivoted at its center rotates in a horizontal plane, and the spheres can slide along the rod. The slender rod initially spins with an angular velocity of 30 rad/s when the spheres are 0.15 m from the center on each side. rod initially spins with an angular velocity of 30 rad/s when the spheres are 0....
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