Why Are the Moments Negative on Fb, Fc, and Fd?

AI Thread Summary
The discussion focuses on understanding why moments are negative for forces Fb, Fc, and Fd. It explains that the torque component of a force at a point is determined by the vector product of the position vector and the force vector. The sign of the moment is influenced by the direction of rotation caused by the force, with anti-clockwise rotations being positive and clockwise rotations being negative. The formulas for calculating moments about the x, y, and z axes are also provided. Overall, the explanation emphasizes the relationship between force direction and moment sign.
noname1
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This is not really a homework question just a review but i wanted someone to explain to me why the forces of the moments negative on Fb, Fc and Fd

thanks in advanced
 

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The component of torque of a force F acting at a point r is equal to the vector product of the vector r and the force.
Mx=y Fz -z Fy,
My=z Fx -x Fz,
Mz=x Fy -y Fx.

You can also decide the sign from the direction of rotation the force would cause along an axis. Seeing from the positive x, y, or z axis, the moment is positive if it rotates anti-clockwise, and negative, if the rotation is clockwise.

ehild
 

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