Lec23

# Lec23 - Physics 2A Olga Dudko UCSD Physics Lecture 23 Today...

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Today: Static Equilibrium Center of Gravity Tips to avoid tipping over Physics 2A Olga Dudko UCSD Physics Lecture 23

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What keeps the rock and the bridge from falling?
Equilibrium • A body is in equilibrium w hen the net external force and torque on the body are both zero: If, in addition, the body is stationary, then it is in static equilibrium. r F ± = d r p dt = 0 r ± ± = d r L dt = 0 COM of rigid body has a=0 can't have tendency to start rotating about any point

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Center of Gravity • T o help us solve torque problems, it is useful to de fi ne the center of gravity (CG). • CG coincides with Center Of Mass (COM) when gravitational fi eld is uniform (i.e., for objects whose size is insigni fi cant compared with Earth’s radius). • The CG of a rigid body is the point at which the gravitational force seems to act. A suspended object is in equilibrium only when its CG lies directly below suspension point F g CG F g CG A nonzero torque tends to rotate the object to the equilibrium orientation
Center of Gravity A body whose CG is above the base of support will be stable if a vertical line projected down from CG falls within the base of support .

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