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        Static equilibrium is covered in this lecture, achieved only when the net external force AND net external torque on an object are both zero. A ladder leaning against the wall is analyzed to determine the minimum angle it can make with the floor without sliding. Professor Lewin continues with the topic by discussing how to locate the center of mass of a rigid body. The center of mass always lines up below the point of suspenson such that the net torque is zero. He concludes by discussing the stability of a ropewalker, improved by lowering her center of mass below the rope.