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Home Q & A Board Science-Related Homework Help Physics
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leon leon
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11 years ago
In class, we took a plastic shape and found its center of gravity. The question is: in terms of torque and rotational equilibrium, explain why the center of gravity hanging plastic shape must lie on a vertical line below the suspension point.
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#1
11 years ago
It if was not on the same vertical line as the suspension point (the center of rotation) it would cause an unbalanced force clockwise or counterclockwise, which would cause it to rotate until it did line up with the center of gravity.
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11 years ago
If it didn't the force acting downwards through the centre of gravity would make it turn until it did so.
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#3
11 years ago
The weight of the shape acts on the center of gravity.  To be in equilibrium, the suspension force must be equal and opposite the weight.  Also, the shape is free to rotate around the suspension point, so the torque about that point must be zero.  Torque is the cross product of the force and the lever arm.  The only way it can be zero is if the force is pointed along the lever arm--which means the thing must hang in a vertical line--straight up or straight down.

Now for the equilibrium to be STABLE, you have to look at what torque is produced if you move the shape slightly from equilibrium.  If the shape is hanging down, a small disturbance produces a righting torque which pushes the shape back down.  But if the shape is balanced up, a small disturbance produces a disturbance which pulls it down away from equilibrium--so this configuration is not stable.
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smooth212smooth212
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11 years ago
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